Primary INRAT References

TP 691E - Study and Reference Guide for Instrument Rating Written Examinations.

Canadian Aviation Regulations (CARs).

Transport Canada Aeronautical Information Manual (TC AIM).

Canada Air Pilot (CAP) - CAP General section.

Canada Flight Supplement (CFS).

Enroute Low/High/Terminal Charts.

Human Factors for Aviation - Basic Handbook.

Air Command Weather Manual.

When in Doubt... Aircraft Critical Surface Contamination Training.

• Flight Test IFR Examiner Guide
• Written IFR Examiner Guide

1.1 Canadian Aviation Regulations - Part I General Provisions

Interpretation and definitions.

1.2 Personnel Licensing and Training

Recency Requirment to act as PLC/SIC (Co-pilot):

• Have flown as PIC/SIC in the last 5 years or, Completed a flight review + written exam.

• For IFR use, within:
  • 6 months: 6 approaches
  • 24 months:
  • IPC - Instrument Proficiency Check by a Pilot Examiner / authorized IFR examiner.
  • or IFR flight test
  • or PPC with IFR component - Pilot Proficiency Check that includes the required instrument/IFR sequences.

1.3 Airspace Structure, Classification, and Use

• CDA -> Canadian Domestic Airspace - controlled/uncontrolled airspace system.
  • Controlled A - E
  • Uncontrolled airspace - G as no control authority, but flight information and alerting may still exist.
  • Special-use airspace: advisory or restricted - F which can be controlled, uncontrolled or mixed.
  • advisory - CYA - Caution - activity nearby area
  • restricted - CYR - Restricted - activity in area, permission required to enter.

• Low-level airspace -> below 18,000 ft ASL.
• High-level airspace -> 18,000 ft ASL and above.
• SDA -> Southern Domestic Airspace. Uses magnetic track for cruising altitude rules
• NDA -> Northern Domestic Airspace. uses true track for cruising altitude rules.
• Other divisions include altimeter setting region, standard pressure region, and mountainous regions.

1.4 Operating and Flight Rules

• 

Cruising altitudes and cruising flight levels.

• Southern Domestic Airspace: use magnetic track.
• Northern Domestic Airspace: use true track.
• 000°–179° = odd IFR cruising altitudes or flight levels.
• 180°–359° = even IFR cruising altitudes or flight levels.
• Track decides — east-ish odd, west-ish even, unless ATC assigns different.
• ATC-assigned altitude or flight level overrides the normal odd/even rule.

1.5 Operational and Emergency Equipment Requirements

Oxygen requirements for flight crew and passengers.

• Cabin-pressure-altitude above 10,000 ft ASL but not above 13,000 ft ASL for more than 30 minutes: oxygen supply must be available for all crew members and 10% of passengers, minimum one passenger.
• At those altitudes, each crew member must use oxygen for the part of flight that is more than 30 minutes.
• Cabin-pressure-altitude above 13,000 ft ASL: oxygen supply must be available for all persons on board, everyone on board must use oxygen for the entire time at those altitudes.

1.6 Flight Preparation, Flight Plans, and Flight Itineraries

Pre-flight information, Weather, flight plan, Arrival Airport, Fuel

• Before flight, the PIC must check the information needed for that flight.
• Think: weather, NOTAMs, route, fuel, alternates, airport/runway info, and aircraft limits.

Operations at or in the Vicinity of an Aerodrome

General operating rules, VFR and IFR aircraft operations at uncontrolled aerodromes within an MF area.

Reporting procedures for IFR aircraft approaching or landing at an uncontrolled aerodrome.

1.8 Instrument Flight Rules

General IFR requirements.

• If you are in instrument weather, you must follow IFR rules.
• IFR requires the proper flight rules, equipment, rating, and clearances where required.

Alternate aerodrome requirement.

• IFR needs a backup airports.
• IFR flight plan/itinerary must list an alternate aerodrome.
• The alternate must have a landing area suitable for your aircraft.

Minimum altitudes to ensure obstacle clearance.

• Use the published IFR chart altitude when one exists.
• If no published minimum exists: stay 1,000 ft above the highest obstacle within 5 NM.
• In designated mountainous areas: stay 2,000 ft above the highest obstacle within 5 NM.

Take-off Minima

Takeoff minima = visibility, not ceiling. CAP is default; AOC/604 is special permission; lower minima need both aerodrome support and operator authorization.

604 = private/corporate operator special permission

CAP = normal published default

Enroute IFR position reports.

IFR Position report format: C-GVBV, BOOTH, 1523Z, 8,000 feet, estimating JAKKU 1545Z, ALDER next.

Approach ban - general

• Approach ban = gate before final; DA/MDA = landing decision.
• Approach ban is checked before continuing past the FAF.
• Approach ban is based on reported visibility/RVR, not ceiling.
• ATC approach clearance does not cancel the approach ban.
• Runway Visual Range(RVR) - the distance a pilot can see along the runway.
• RVR 2600 is commonly treated as about 1/2 SM.
• You may continue if RVR improves above minimums before reaching the FAF.
• If RVR drops after passing the FAF, continue only if legally allowed and required visual reference exists at DA/MDA.
• Circling approach requires maintaining required visual reference with the airport/runway environment.
• DA/MDA is the landing decision point after the approach-ban gate has been satisfied.

1.9 Radio communications

Two-way radiocommunication failure in IFR flight.

• If two-way radio communications fail in IFR, squawk 7600.
• Route to fly is determined by AVEF priority.
• AVEF = Assigned, Vectored, Expected, Filed.
• Maintain the appropriate altitude/route and continue according to the applicable IFR communications-failure procedure.
• AVEF route-order priority: Assigned, Vectored, Expected, Filed.
  • Assigned - last ATC-assigned route.
  • Vectored - route to fix/vector ATC was giving before failure.
  • Expected - route you were told to expect in a clearance.
  • Filed - route originally filed in your flight plan.

1.10 Aircraft Requirements

Power-driven aircraft - IFR. De-icing or anti-icing equipment.

1.11 Air Traffic Services

Air Traffic Control (ATC) and advisory services.

• Clearance = permission with a stop point.
• Clearance limit = farthest point you may go.
• Published hold? Hold as published.
• No published hold, then use Standard hold on inbound track.
• Do not pass the clearance limit without more clearance.
• Unable or unsafe? Tell ATC early.
• Emergency or amended clearance can change the plan.
• No landing clearance = do not land.
• Lost comms in VMC = stay VMC, land as soon as practicable.
• Lost comms in IMC = follow IFR lost-comms procedure.
• Expected Further Clearance(EFC) given = hold until EFC, then continue.
• No EFC + limit is approach fix = approach near ETA.
• No EFC + limit not approach fix = go to an approach fix, then approach near ETA.

Flight Service Stations (FSS).

• FSS advises at uncontrolled aerodromes and MF areas.
• FSS is not ATC: it gives information, not control or separation.
• FSS may relay a clearance, but ATC owns the clearance.
• FSS gives the field picture: runway, wind, traffic, vehicles, wake, weather, and conditions.
• FSS/FIC can help with alerting and emergencies.
• FIC = briefing, weather, NOTAMs, flight plans, and enroute information.
• RAAS = remote FSS-style advisory with no direct eyes on the airport.

Flight Information Centres (FIC).

• FIC = preflight briefing + enroute information.
• FIC gives weather, NOTAMs, flight planning help, and FISE.
• FISE = enroute updates: SIGMET, AIRMET, PIREP, METAR, TAF, altimeter, radar, lightning, RSC/CRFI.
• FIC can accept flight plan information and flight updates.
• FIC may relay IFR/SVFR clearances, but ATC issues them.
• FIC receives PIREPs, position reports, arrival/departure times, and flight plan revisions.
• FIC gives information only; it does not control or separate aircraft.

Clearances and instructions.

• Clearance = permission.
• Instruction = direction issued by ATC that the pilot must acknowledge and comply with.
• Advisory = information only.
• ATC clears; pilot reads back and complies.
• If unclear, ask: Say again / confirm.
• If unable or unsafe, say unable early.
• Emergency can override, but advise ATC ASAP.
• FSS/FIC may pass the clearance; ATC owns it.
• ATC clearance does not cancel weather minima, obstacle clearance, aircraft limits, or PIC responsibility.

Communication procedures for departure, enroute, and arrival.

• Departure: get ATIS/AWOS/advisory, get IFR clearance, read it back, then switch to departure/centre when told.
• Enroute: listen on the assigned frequency, follow frequency changes, and make required position reports.
• Arrival: get ATIS/AWOS/advisory early, contact approach/tower/FSS/MF, and report intentions as required.
• Read back the big safety items: route, altitude, squawk, runway, hold short, heading, approach clearance, and frequency.
• Report important IFR events: clearance limit, entering/leaving a hold, missed approach, altitude changes, and unable-to-comply.
• At uncontrolled or MF aerodromes, make position and intention reports so everyone has the traffic picture.
• Approach clearance is not landing clearance.
• If unclear, ask ATC/FSS to say again or clarify.

Radar services for departure, enroute, and arrival.

• Radar service = ATS surveillance service.
• ATC must identify you before radar service begins.
• ATC tells you when you are identified or identification is lost.
• Radar identified does not mean pilot responsibility disappears.
• On vectors, ATC handles obstacle clearance until you resume normal navigation.
• Vectors = ATC-assigned headings for separation, noise, pilot request, or better traffic flow.
• ATC should tell you where you are being vectored.
• 'Resume normal navigation' = stop following vectors and navigate yourself again.
• Vectors to final + approach clearance = resume normal approach navigation.
• Radar service usually continues until you leave coverage, enter uncontrolled airspace, or transfer to non-radar ATC.
• If radar service ends, ATC tells you.
• Traffic information is helpful, but ATC may not see or report every aircraft.

Wake turbulence separation.

• Wake comes from big wings: heavy aircraft make strong wingtip vortices.
• Wake is worst on takeoff and landing, but can happen enroute behind large aircraft.
• Wake sinks and drifts with the wind.
• Calm wind can be worse: wake may sit on the runway.
• 'Caution wake turbulence' means pilot must avoid it — ATC does not guarantee safety.
• Takeoff behind Heavy: lift off before its rotation point and stay above its path.
• Landing behind Heavy: stay above its glide path and land beyond its touchdown point.
• Landing behind a departing aircraft: touch down before its rotation point.
• ATC separates, but wake can still bite.
• IFR departure wake spacing is ATC’s responsibility, but avoidance is still the pilot’s job.

Transponder operation

• Transponder = ATC can see and identify you.
• Mode A = squawk code.
• Mode C = altitude reporting.
• Mode S = Mode A/C plus data link; used with TCAS II/ACAS II.
• Set the assigned code before leaving STANDBY.
• IFR low-level default = 1000 with Mode C, unless ATC says otherwise.
• IFR high-level default = 2000 with Mode C, unless ATC says otherwise.
• Keep your assigned discrete code until ATC tells you to change.
• IDENT only when ATS asks.
• Transponder/Mode C failure in required airspace: continue to next intended landing, then get ATC authorization for further flight if needed.
• Need transponder airspace without working transponder/Mode C? Get approval before entering.
• 7500 = unlawful interference.
• 7600 = radio failure.
• 7700 = emergency.
• 7600 tells ATC you lost comms, but you still follow IFR lost-comm procedures.

Wake turbulence separation.

• Wake sinks and drifts.
• Heavy ahead? Stay above its path.
• Landing behind Heavy = stay above glidepath, land beyond touchdown.
• Takeoff behind Heavy = rotate before Heavy’s rotation point, then stay above.
• Light wind can be worse because wake can sit on the runway.
• Crosswind can drift wake onto nearby runways.
• ATC may warn: CAUTION WAKE TURBULENCE.
• ATC separates, but pilot still avoids the wake.
• Light behind Medium = 4 NM.
• Medium behind Heavy = 5 NM.
• Light behind Heavy = 6 NM.
• Same runway behind Heavy = usually 2 minutes.
• Intersection departure behind Heavy = usually 3 minutes.
• Intersection adds time.

Reduced visibility operations.

• RVOP = Reduced Visibility Operations Plan.
• LVOP = Low Visibility Operations Plan.
• RVOP applies when aerodrome visibility is below RVR 2600 down to and including RVR 1200.
• LVOP applies when aerodrome visibility is below RVR 1200.
• RVOP/LVOP are mainly aerodrome ground-movement procedures used to protect aircraft and vehicles in poor visibility.
• Procedures can vary by airport, so check ATIS, CAP, CFS, NOTAMs, and ATC instructions.
• ATC may be unable to issue taxi, takeoff, or landing clearance when RVOP/LVOP restrictions are in effect.
• RVR is the key visibility value used for runway operations.
• RVR A = touchdown/threshold area, RVR B = midpoint, RVR C = rollout/stop-end area.
• Low-visibility procedures are associated with CAT III operations and restrict aircraft/vehicle movement on the airport movement area.

1.12 Canadian Airspace

Low-level controlled airspace types, dimensions, and flight rules.

Classification of airspace.

Special use airspace.

• A to E = Controlled
• F as advisory/restricted special-use airspace,
• G as Go Alone / Uncontrolled
• Canadian Domestic Airspace Structure:
  • SDA uses magnetic tracks..
  • NDA uses true tracks..

1.13 Route and Flight Planning

Publications and charts: requirements and use.

Preferred routing and factors affecting flight plans.

Navigation plan and flight log.

Altitude selection.

IFR flight in mountainous regions.

Fuel requirements for aeroplanes and helicopters.

Weather requirements for takeoff, landing, and alternate.

NOTAM classifications and interpretation.

Use of flight computer.

Canada Air Pilot utilization and definitions.

1.14 Departure Procedures

ATIS.

Radar departure.

Non-radar departure.

Standard Instrument Departure (SID).

Departure at uncontrolled aerodrome.

Obstacle clearance.

Visibility requirements and RVR.

1.15 Enroute Procedures

Position reports.

Clearance limits.

Changes to flight plan.

Altitude limitations: MEA, MOCA, MRA, GASA.

Adherence to TAS.

Fixes and waypoints.

1,000 feet on top - IFR flight.

IFR flight from controlled airspace to uncontrolled airspace.

IFR flight from uncontrolled airspace to controlled airspace.

1.16 Holding Procedures

Holding clearance.

Entry.

Standard holding pattern.

Non-standard holding pattern.

Timing.

Speed limitations.

DME.

Shuttle.

1.17 Approach Procedures

ATIS.

• ATIS = Automatic Terminal Information Service.
• ATIS gives routine airport information for arriving and departing aircraft.
• ATIS may include weather, approach in use, landing runway, departure runway, NOTAMs, NAVAID status, and field conditions.
• Each ATIS has a code letter, such as Information ALFA, BRAVO, CHARLIE.
• On initial contact, tell ATC/FSS you have the current ATIS letter.
• ATIS gives information, not clearance.
• Current RVR is not normally included in ATIS; it is issued separately when required.
• If weather or airport conditions are changing quickly, ATIS may tell pilots to contact ATC/FSS for current information.

STARs.

• STAR = Standard Terminal Arrival Route.
• A STAR is an IFR arrival procedure published in the CAP.
• STARs connect the enroute structure to the terminal/approach environment.
• If cleared for a STAR, fly the charted lateral route.
• Do not descend on the STAR vertical profile until ATC gives descent clearance.
• Charted altitude and speed restrictions remain mandatory unless ATC cancels or changes them.
• ATC speed assignments override charted STAR speeds until cancelled or no longer legal.
• Open STARs usually expect vectors and do not automatically join final.
• Approach clearance is required before linking the STAR to the approach.

Radar vectors.

• Radar vectors are ATC-assigned headings used to guide the aircraft.
• ATC must identify the aircraft before providing ATS surveillance service.
• When identified, pilots may hear 'IDENTIFIED' or 'RADAR IDENTIFIED'.
• Vectors may be used for separation, sequencing, noise abatement, pilot request, or operational advantage.
• When being vectored, fly the assigned heading until ATC gives a new instruction or clears you to resume navigation.
• ATC assumes terrain/obstacle clearance responsibility while vectoring IFR aircraft for arrival until normal navigation resumes.
• When vectors end, ATC normally says 'RESUME NORMAL NAVIGATION'.
• If vectored to final approach course, the approach clearance indicates normal navigation should resume.
• Approach clearance is not landing clearance.
• Radar service does not guarantee all traffic or weather will be seen.

Speed adjustment.

• ATC may assign speeds to help with sequencing, spacing, and vectors.
• Speed adjustments are normally given in 10-KIAS increments.
• Maintain the assigned speed within 10 KIAS.
• You may be told to maintain present speed, increase speed, reduce speed, or change speed by a specified amount.
• ATC-assigned speed may override a STAR speed restriction, unless the speed is no longer legal or safe.
• Pilot must not fly an unsafe speed just because ATC assigned it.
• If unable to comply, tell ATC immediately.
• Legal speed limits still apply: 250 KIAS below 10,000 ft ASL; 200 KIAS below 3,000 ft AGL within 10 NM of a controlled airport, unless minimum safe speed is higher.

Transition to approach.

• Transition to approach = moving from STAR/vector/arrival routing onto the actual instrument approach.
• A STAR does not automatically clear you for the approach.
• ATC must issue approach clearance before you start the approach.
• After approach clearance, comply with remaining STAR altitude and speed restrictions unless ATC cancels them.
• Use the assigned transition, published interface waypoint, or ATC vectors to intercept final.
• Open STARs usually expect vectors or a published transition to final.
• If approach clearance is not received, continue the STAR as charted and wait for ATC instructions.
• Approach clearance is not landing clearance.

Initial approach and procedure turn.

• Initial approach = the segment that positions the aircraft for the intermediate/final approach.
• Procedure turn = course reversal used to get established inbound.
• Straight-in approach = no procedure turn.
• NoPT means no procedure turn is required from that route or sector.
• If cleared straight-in, do not fly a procedure turn.
• If arriving from a sector where HILPT/procedure turn is required, fly it unless ATC clears otherwise.
• If the approach says ATS SURVEILLANCE REQUIRED, ATC vectors provide the initial approach segment.
• Do not invent your own procedure turn; follow the chart or ATC clearance.

Straight-in approach with no procedure turn.

• Straight-in approach = join final without flying a procedure turn.
• NoPT means no procedure turn is required from that route, fix, or sector.
• If cleared straight-in, do not fly a procedure turn.
• Vectors to final usually set you up for a straight-in approach.
• A published transition to an IF may allow a straight-in approach.
• Still follow published altitudes, step-down fixes, and approach minima.
• Straight-in approach clearance is not landing clearance.

Straight-in minima

• Straight-in approach = no procedure turn.
• Straight-in minima = landing minima for that runway.
• Straight-in approach clearance ≠ straight-in minima guaranteed.
• Use the published minima for your aircraft category.
• If straight-in minima are not published, use circling minima.
• Circling minima only does not ban a straight-in landing if visual reference allows a normal landing.
• Need wind, runway condition, and runway clear before landing.
• At uncontrolled airports, verify runway condition/obstructions before landing.

Final approach.

• Final approach = last IFR segment before decision.
• Non-precision final starts at FAF/FAWP/FAP.
• Precision final starts near glidepath intercept.
• FAF = final descent begins on many non-precision approaches.
• Stay on the published course and vertical path/profile.
• Step-down fixes still count.
• DA = decide now.
• MDA = maintain until MAP.
• MAP = missed approach point.
• No required visual reference by DA/MDA/MAP = missed approach.
• Approach clearance ≠ landing clearance.

Precision Approach: ILS and PAR

• Precision approach = lateral + vertical guidance.
• ILS = LOC + glide path.
• LOC = runway centreline guidance.
• Glide path = descent guidance.
• ILS uses DA/DH, not MDA.
• PAR = controller talks you down using radar.
• PAR gives controller azimuth, altitude, and range.
• PAR is mostly military, but may be available to civilians where published.
• No required visual reference at DA/DH = missed approach.
• Approach clearance ≠ landing clearance.

Non-precision approach: NDB, VOR, DME, LOC, RNAV/GNSS.

• Non-precision = lateral guidance only.
• No glidepath = use MDA, not DA.
• MDA = Maintain Descent Altitude until MAP.
• MAP = missed approach point.
• No visual by MAP = missed approach.
• NDB = bearing guidance.
• VOR = radial/course guidance.
• DME = distance fixes/step-downs.
• LOC-only = localizer lateral guidance only.
• RNAV/GNSS LNAV or LP = non-precision style, usually MDA.
• LNAV/VNAV or LPV = vertical guidance/APV, not basic NPA.
• Step-down fixes still count.
• Approach clearance ≠ landing clearance.

Stabilized Constant Descent Angle approach.

• SCDA = Stabilized Constant Descent Angle.
• SCDA is used mainly on non-precision approaches.
• Instead of dive-and-drive, fly a smooth constant descent.
• Aim to arrive near MDA at the MAP or visual descent point.
• MDA still applies — do not descend below it early.
• Advisory vertical guidance is advisory only.
• Barometric altimeter is the primary altitude reference.
• Step-down fixes and altitude restrictions still count.
• No required visual reference at MDA/MAP = missed approach.
• SCDA makes NPA look cleaner, but it does not turn it into precision.

Visual Approach and Contact Approach

Visual approach is more like: I can proceed visually to the airport.

Contact approach is more like:I may not see the airport yet, but I can stay clear of cloud and navigate visually by the ground/surface.

• Visual = Airport in sight / VMC / ATC says yes
• V-A-A
• Contact = Cloud-clear, 1 mile, surface contact
• C-1-S
  • V = VMC
  • A = Airport/traffic visually manageable
  • A = ATC authorization required
  • C = Clear of cloud
  • 1 = At least 1 SM flight visibility
  • S = Surface visual reference

• Contact = Cloud-clear, 1 mile, surface contact
• C-1-S
  • C = Clear of cloud
  • 1 = At least 1 SM flight visibility
  • S = Surface visual reference

Circling Approach Requirements and Limitations

Circling = IFR approach + visual manoeuvre

You are not just joining the circuit.

You are still on an IFR approach, but after reaching circling minima, you visually manoeuvre to land on another runway.

Circle only if you can: See it, stay inside it, stay above MDA, and go missed if you lose it.

Circling = “I am IFR until I can safely land visually.

• A-C-V-M-P-M
  • A = ATC authorization required
  • C = Category controls minima and protected area
  • V = Visual reference must be maintained
  • M = MDA must be respected
  • P = Protected circling area — stay inside it
  • M = Missed approach if visual reference is lost

Circling approach.

• Circling = IFR approach, visual manoeuvre.
• Used when runway is not suitable for straight-in landing.
• Descend to circling MDA, then visually manoeuvre.
• Keep the runway in sight after initial visual contact.
• Stay at circling MDA until normal landing is assured.
• Protected area depends on aircraft approach category.
• If circling faster than your category, use the higher category minima.
• Do not circle into a restricted sector.
• ATC may suggest direction/area, but pilot is responsible for safe manoeuvring.
• If visual reference is lost or landing is doubtful, go missed.

Missed approach.

• Missed approach = climb, navigate, communicate.
• No visual at DA = go missed immediately.
• No visual by MAP on MDA approach = go missed.
• Follow the published missed approach unless ATC gives specific missed instructions.
• Continue along the final approach course to the MAP, then fly the missed procedure.
• You may climb immediately to the missed approach altitude.
• If no further clearance at the missed approach hold, hold as published or standard as required.
• ATC instructions do not automatically guarantee obstacle clearance.
• Pilot must ensure terrain and obstacle clearance.
• Check missed approach climb gradient before the approach.
• Faster groundspeed = higher required climb rate.
• Approach clearance ≠ missed approach clearance change.

Uncontrolled aerodromes and VFR/IFR traffic mix.

• Uncontrolled airport = no tower separation.
• IFR clearance ≠ traffic priority.
• IFR aircraft do not have priority over VFR traffic.
• Fit into the active runway/circuit when VFR circuit traffic is operating.
• Broadcast clearly on MF/ATF.
• In uncontrolled airspace, monitor 126.7 before descent or approach when practical.
• Broadcast intentions before changing altitude or commencing approach.
• Once on MF, make required IFR position reports.
• Report before approach, outbound/final, FAF, final, circling, and missed as required.
• Straight-in landing may be unsafe without wind/runway condition information.
• If runway condition is unknown, visually inspect or circle using circling MDA.
• Pilot is responsible for traffic avoidance and safe sequencing.

Obstacle Clearance: Minimum Safe Altitude and Minimum Sector Altitude (MSA)

• MSA = Minimum Sector Altitude.
• MSA gives at least 1,000 ft obstacle clearance.
• MSA normally covers at least 25 NM from a NAVAID or waypoint near the aerodrome.
• MSA may be split into pie-shaped sectors.
• Pick the sector by your track/bearing to the reference NAVAID or waypoint.
• MSA is for obstacle clearance, not navigation guidance.
• MSA is not flight-inspected.
• Conventional NAVAID-based MSA may not guarantee signal coverage.
• Safe Altitude 100 NM = obstacle clearance within 100 NM of the aerodrome reference point.
• In mountains, required obstacle clearance may be 1,500 ft or 2,000 ft.
• MSA/Safe Altitude may let you descend before approach, but position must be known.
• Low temperature can reduce true altitude, so cold-temperature correction may be needed.

Temperature compensation.

• Cold = true altitude lower than indicated.
• High to low, look out below; warm to cold, you are lower than told.
• Temperature correction protects obstacle clearance.
• Correct published minimum IFR altitudes when cold enough.
• Correct MSA/TAA, initial, intermediate, final, missed approach, MDA, and DA.
• General trigger: 0°C or colder.
• If MDA/DA is 1,000 ft HAA or higher, correction begins at 10°C.
• Add correction to the published altitude; never subtract.
• Use the CAP altitude correction chart/table.
• Use temperature from the nearest reporting station, normally the aerodrome.
• Do not correct an ATC-assigned altitude you accepted, like 'maintain 3000'.
• ATC vectoring altitudes are already temperature-corrected.
• If correcting a published mandatory altitude or missed approach holding altitude, advise ATC.

Approach Ban and Visibility Requirements

• Approach ban = gate before final.
• Check before passing the FAF inbound.
• If no FAF, check before intercepting final approach course.
• For general aviation, approach ban is mainly RVR-based.
• Aeroplane GA minimum: RVR A only = 1200.
• Aeroplane GA minimum: RVR A and B = 1200/600.
• Aeroplane GA minimum: RVR B only = 1200.
• If RVR drops below minima after passing FAF, you may continue to DA/MDA.
• If RVR is varying above and below minimum, approach may be authorized.
• If RVR is below minimum but ground visibility is at least 1/4 SM, approach may be authorized.
• If RVR is unavailable or not reported, there may be no RVR-based approach-ban criterion.
• Approach ban decides if you may continue inbound; DA/MDA decides if you may land.
• ATC approach clearance does not cancel the approach ban.
• Low-visibility procedures in effect can prohibit NPA, APV, CAT I, or CAT II approaches.

1.18 Canada Air Pilot (CAP)

CAP GEN definitions.

• CAP GEN = the decoder for approach plates.
• Use CAP GEN for definitions, symbols, minima, categories, and chart notes.
• Chart legend = decode approach, aerodrome, lighting, and symbols.
• Operating minima = know the legal landing limits.
• Aircraft category = speed-based minima/protected area.
• Category A = up to 90 KIAS.
• Category B = 91–120 KIAS.
• Category C = 121–140 KIAS.
• Category D = 141–165 KIAS.
• Category E = above 165 KIAS.
• DA = decision altitude, shown as altitude ASL.
• DH = decision height, referenced to threshold elevation.
• MDA = minimum descent altitude; do not descend below until visual and safe.
• HAT = height above touchdown.
• HAA = height above aerodrome.
• FAF = final approach fix.
• MAP/MAPT = missed approach point.
• RVR = runway visual range.
• RVR A/B/C = touchdown or threshold, midpoint, rollout/end.
• NoPT = no procedure turn.
• NA = not authorized.
• CAP GEN tells you how to read the chart; the approach plate tells you what to fly.

Chart legend for approach, aerodrome, lighting, and symbols.

• Chart legend = CAP map key.
• Approach plate symbols tell you what to fly.
• Aerodrome chart symbols tell you where to taxi and park.
• Lighting symbols tell you what visual aids are available.
• Plan view = lateral route picture.
• Profile view = vertical descent picture.
• Minima box = legal bottom line.
• IAF = where the approach begins.
• IF = where you line up for final.
• FAF/FAWP = final descent starts.
• MAP/MAPT = missed approach decision point on NPA.
• NoPT = no procedure turn.
• HILPT = hold-in-lieu of procedure turn.
• DME arcs and fixes define distance-based routing.
• Step-down fixes protect obstacles before MDA/DA.
• Missed approach track is not optional.
• Aerodrome chart = runways, taxiways, aprons, hold lines, hotspots, and restrictions.
• Lighting legend = ALS, ODALS, PAPI, VASIS, runway edge, threshold, and runway end lights.
• RVR A/B/C = touchdown or threshold, midpoint, rollout or runway end.
• Read chart notes before flying the procedure.

Altitude corrections.

• Altitude correction = add height for safety.
• CAP altitudes are minimum altitudes.
• Published altitudes assume ISA conditions and current altimeter setting.
• Cold temperature makes true altitude lower than indicated.
• Cold = add correction.
• Never subtract an altitude correction.
• Use the CAP altitude correction chart/table.
• Apply corrections to published minimum IFR altitudes when required.
• Correct MSA/TAA, initial, intermediate, final, missed approach, MDA, and DA when cold enough.
• General cold trigger: 0°C or colder.
• If MDA/DA is 1,000 ft HAA or higher, correction begins at 10°C.
• Do not correct an accepted ATC assigned altitude, such as 'maintain 3000'.
• ATC vectoring altitudes are already temperature-corrected.
• If correcting a mandatory altitude or missed approach holding altitude, advise ATC.
• Remote altimeter setting corrections must be applied when published in the RASS box.
• Falling pressure may require adding to DH/MDA.
• 0.01 inHg pressure fall = about 10 ft correction.

Operating minima

• Operating minima = legal weather/altitude limits.
• CAP minima tell you how low you may go and what visibility/RVR is required.
• Minima depend on approach type, aircraft category, runway equipment, lighting, and approvals.
• DA/DH = decision point for precision/APV-style approaches.
• MDA = minimum descent altitude for non-precision/circling.
• Visibility/RVR = required seeing distance.
• Aircraft category changes the protected area and minima.
• Approach ban = may you continue past FAF?
• Landing minima = may you descend below DA/DH/MDA?
• Required visual reference must be established and maintained before descending below DH/MDA.
• Alternate minima are planning minima, not landing minima.
• CAP GEN alternate memory: 400-1, 600-2, 800-2.
• Two precision approaches = 400-1 or 200-1/2 above lowest usable HAT/visibility, whichever is greater.
• One precision approach = 600-2 or 300-1 above lowest usable HAT/visibility, whichever is greater.
• Non-precision only = 800-2 or 300-1 above lowest usable HAT/HAA and visibility, whichever is greater.
• CAT II/CAT III minima require special aircraft, pilot, runway, and operator approval.
• Inoperative lighting can raise minima or visibility requirements.
• ATC clears the approach; CAP controls the minima.

Aircraft Categories

• Aircraft category = approach speed category.
• Category controls minima and protected airspace.
• Based on Vref, if published.
• If no Vref, use 1.3 × Vs0 at maximum certificated landing weight.
• Category A = up to 90 KIAS.
• Category B = 91–120 KIAS.
• Category C = 121–140 KIAS.
• Category D = 141–165 KIAS.
• Category E = above 165 KIAS.
• Rotorcraft are included in Category A.
• You cannot use a lower/slower category to get lower minima.
• If you fly faster than your normal category, use the higher category minima.
• Faster circling speed = higher circling category.
• Aircraft category ≠ ILS CAT I/II/III.
• Approach category = speed; ILS category = weather/equipment approval.

1.19 Emergencies

Declaration of an emergency.

• Emergency declaration = ask for priority help early.
• MAYDAY = distress.
• Distress = serious/imminent danger + immediate assistance required.
• PAN PAN = urgency.
• Urgency = safety concern, but not immediate assistance yet.
• Say MAYDAY or PAN PAN at the beginning of the first emergency call.
• Say the signal three times if practical: MAYDAY MAYDAY MAYDAY or PAN PAN PAN PAN PAN PAN.
• Use the frequency already in use if possible.
• If needed, use any available frequency or broadcast.
• Emergency frequencies: 121.5 MHz and 243.0 MHz.
• In uncontrolled airspace, monitor 126.7 when practical.
• Squawk 7700 if you need to alert ATC and cannot communicate immediately.
• Emergency call should include: who you are, what is wrong, what you intend, position, altitude, and heading.
• Aviate first, navigate second, communicate third.
• Declaring an emergency is not failure — it buys time, priority, and options.

Use of transponder.

• 7700 = emergency.
• 7600 = communication failure.
• 7500 = unlawful interference.
• Emergency transponder code alerts ATC on surveillance displays.
• If you can talk to ATC, declare the emergency by radio first.
• If you cannot contact ATC immediately, squawk 7700.
• After squawking 7700, contact ATC as soon as possible.
• After ATC knows the situation, operate the transponder as directed.
• Squawk 7600 for radio failure, then follow IFR lost-communication procedures.
• 7600 does not cancel AVEF/AEM lost-comm rules.
• Squawk 7500 only for unlawful interference.
• ATC does not normally assign 7500 unless the pilot reports unlawful interference.
• If ATC asks 'confirm squawk 7500', answer clearly if able.
• No reply to a 7500 confirmation may be treated as intentional.
• IDENT only when ATC asks.
• Aviate, navigate, communicate — transponder helps, but flying comes first.

Deviation from clearance.

• Clearance = follow it unless safety says no.
• Emergency authority = do what is necessary for safety.
• Aviate first, clearance second.
• If an ATC clearance or instruction would jeopardize safety, deviate as required.
• Tell ATC as soon as possible after deviating.
• Give reason: emergency, TCAS RA, terrain warning, weather, engine problem, etc.
• Deviation should be only as much as needed.
• After the conflict/emergency, return to the last clearance or get a new clearance.
• TCAS/ACAS RA may require deviation from ATC clearance.
• TAWS/GPWS warning may require immediate terrain-avoidance action.
• ATC cannot fly the aircraft for you.
• PIC remains responsible for safe flight.
• Declare emergency early if priority handling is needed.
• Do not wait for permission if immediate safety action is required.

Equipment Failure

• Equipment failure = fly first, troubleshoot second.
• Aviate, navigate, communicate.
• Use the checklist/QRH/AFM procedure.
• Declare PAN PAN or MAYDAY if safety or priority handling is needed.
• Tell ATC what failed and what help you need.
• If unable to comply with clearance, say unable and request amended clearance.
• If emergency requires deviation, deviate first, advise ATC as soon as practical.
• Communication failure = squawk 7600 and follow IFR lost-comm procedures.
• Emergency with no immediate communication = squawk 7700.
• 121.5 MHz may be used if normal communication channels are unavailable due to equipment failure.
• Navigation failure = tell ATC, request vectors or alternate routing.
• Instrument failure = use standby instruments and partial-panel scan.
• Autopilot failure = hand-fly; reduce workload early.
• Electrical failure = preserve essential equipment and consider diversion.
• Vacuum/gyro failure = trust remaining reliable instruments.
• Pitot-static failure = use alternate static source if available and cross-check performance.
• Transponder failure = advise ATC; follow ATC instructions and airspace rules.
• If aircraft is no longer legal or safe for IFR, divert or get to VMC/landing as appropriate.

2.1 Fundamentals of Weather

Meteorological services available.

• Weather services = gather, compare, decide.
• Main source for aviation weather briefing in Canada = NAV CANADA FIC.
• FIC = Flight Information Centre.
• FIC provides pilot briefing before flight and updates en route.
• FIC specialists can interpret weather, charts, satellite, lightning, and radar imagery.
• FIC can also provide aeronautical info such as NOTAM, RSC, and CRFI.
• CFPS = NAV CANADA flight planning / aviation weather website.
• CFPS provides aviation weather products, NOTAMs, and flight-plan filing.
• CFS/CWAS list FIC phone numbers and hours of service.
• ATS may provide current wind and altimeter information.
• ATIS includes recent METAR/SPECI details when available.
• FISE frequency can be used for in-flight weather information.
• Initial full briefings while airborne are discouraged due to frequency congestion.
• Important weather products: METAR, SPECI, TAF, GFA, AIRMET, SIGMET, PIREP, upper winds/temperatures.
• Also check radar, satellite, and lightning information when available.
• Pilot responsibility: use the most recent appropriate weather information.
• Weather briefing helps the decision; it does not make the decision.

• 

Factors that determine the weather.

• Weather is built from heat, moisture, pressure, and lift.
• Temperature controls air density and moisture-holding ability.
• Warm air can hold more water vapour than cold air.
• Moisture provides the raw material for cloud, fog, precipitation, and icing.
• Pressure differences create wind.
• Low pressure usually means rising air, cloud, precipitation, and instability risk.
• High pressure usually means sinking air, stability, and clearer weather.
• Stability decides whether air resists vertical motion or keeps rising.
• Stable air = layered clouds, steady precipitation, smoother air, poor visibility risk.
• Unstable air = cumuliform clouds, showers, turbulence, thunderstorms.
• Lift is needed to cool air to saturation.
• Main lifting agents: fronts, terrain, convergence, convection, and low pressure.
• Air masses bring temperature and moisture characteristics.
• Fronts are boundaries between air masses and often concentrate weather.
• Wind moves weather systems and creates mechanical turbulence.
• Terrain can force lifting, turbulence, mountain wave, and local cloud/precipitation.
• IFR weather = moisture + lift + cooling + stability/instability.

Meteorological aspect of altimetry.

• Altimetry weather trap = pressure and temperature lie to your altimeter.
• Pressure altimeter shows altitude based on pressure, not actual geometric height.
• Set the current altimeter setting to reduce pressure error.
• High to low, look out below.
• Flying from high pressure to low pressure without resetting makes you lower than indicated.
• Low to high, clear the sky.
• Flying from low pressure to high pressure without resetting makes you higher than indicated.
• Warm to cold, look out below.
• Cold air makes true altitude lower than indicated.
• Warm air makes true altitude higher than indicated.
• CAP altitudes assume ISA temperature and current altimeter setting.
• Cold temperature correction protects obstacle clearance.
• Add cold-temperature correction to published minimum IFR altitudes when required.
• Never subtract an altitude correction.
• Falling pressure with an old altimeter setting can make you lower than indicated.
• Pressure fall correction memory: 0.01 inHg = about 10 ft.
• Remote altimeter setting may require a published correction.
• IFR trap: indicated altitude can be legal-looking but terrain clearance can be reduced.

Temperature.

• Temperature = heat level of the air.
• Temperature controls air density.
• Warm air is less dense and tends to rise.
• Cold air is denser and tends to sink.
• Warm air can hold more water vapour than cold air.
• Cooling air toward its dew point creates cloud, fog, or precipitation.
• Temperature-dew point spread tells how close air is to saturation.
• Small spread = fog/cloud risk.
• Large spread = drier air and less immediate cloud/fog risk.
• Temperature usually decreases with altitude in the troposphere.
• Standard temperature lapse rate = about 2°C per 1,000 ft.
• Dry adiabatic lapse rate = about 3°C per 1,000 ft.
• Saturated adiabatic lapse rate = about 1.5°C per 1,000 ft, variable.
• Temperature lapse rate affects stability.
• Rapid cooling with height = unstable air.
• Little cooling or warming with height = stable air.
• Temperature inversion = temperature increases with height.
• Inversions trap fog, haze, smoke, low cloud, and poor visibility.
• Cold temperature makes true altitude lower than indicated.
• Hot temperature increases density altitude and reduces aircraft performance.
• Icing risk needs visible moisture and suitable cold temperatures.

Moisture.

• Moisture = water vapour in the air.
• Moisture is the fuel for cloud, fog, precipitation, thunderstorms, and icing.
• Warm air can hold more water vapour than cold air.
• Cold air holds less water vapour, so cooling air can cause saturation.
• Saturation = air is holding as much water vapour as it can at that temperature.
• Relative humidity = how full the air is compared with its maximum capacity.
• 100% relative humidity = saturated air.
• Dew point = temperature the air must cool to for saturation.
• Temperature-dew point spread = fog/cloud warning tool.
• Small temperature-dew point spread = high chance of fog, cloud, or precipitation.
• Large temperature-dew point spread = drier air.
• Cooling air to dew point forms visible moisture: cloud, fog, dew, frost, or precipitation.
• Lifting air cools it and can bring it to saturation.
• Main lifting sources: fronts, terrain, convection, convergence, and low pressure.
• Moist unstable air = shower/thunderstorm potential.
• Moist stable air = stratus, fog, drizzle, poor visibility, and icing risk.
• Visible moisture plus freezing temperatures = icing concern.
• Dew point close to temperature at night = radiation fog risk.
• Moisture does not guarantee weather; it needs cooling/lift and the right stability.

Stability and instability.

• Stability = does lifted air return or keep rising?
• Stable air resists vertical motion.
• Unstable air keeps rising once lifted.
• Stable air = layered clouds, steady precipitation, smoother air, poor visibility risk.
• Unstable air = cumulus clouds, showers, turbulence, thunderstorms.
• Stability depends on temperature lapse rate.
• Environmental lapse rate = actual temperature change with height.
• Dry adiabatic lapse rate = about 3°C per 1,000 ft.
• Saturated adiabatic lapse rate = about 1.5°C per 1,000 ft, variable.
• Standard lapse rate = about 2°C per 1,000 ft.
• Inversion = temperature increases with height; very stable air.
• Stable air often forms stratus, fog, drizzle, haze, and widespread low cloud.
• Unstable air often forms towering cumulus, CB, showers, gusts, and turbulence.
• Heating from below makes air more unstable.
• Cooling from below makes air more stable.
• Lifting moist unstable air can create heavy showers or thunderstorms.
• Subsiding air tends to warm and stabilize.
• IFR trap: stable air can be smooth but still dangerous due to low ceilings, fog, icing, and poor visibility.

Clouds and surface-based layers.

• Clouds = visible moisture from cooled/saturated air.
• Cloud type tells you stability, lift, visibility, icing, and turbulence risk.
• Stable air usually gives layered cloud: stratus, stratocumulus, nimbostratus.
• Unstable air usually gives heap/tower cloud: cumulus, towering cumulus, cumulonimbus.
• Stratus = low layer cloud; IFR ceiling/visibility trap.
• Cumulus = vertical motion; expect bumps and showers if growing.
• Cumulonimbus = thunderstorm cloud; avoid.
• Nimbostratus = widespread steady precipitation.
• Alto = middle-level cloud prefix.
• Cirro = high-level ice-crystal cloud prefix.
• Ceiling = lowest broken or overcast layer, or vertical visibility into an obscuration.
• FEW and SCT are not ceilings.
• BKN and OVC are ceilings.
• Surface-based layer = cloud/obscuration based at the surface, like fog or low stratus.
• Fog = cloud on the ground.
• Mist, haze, smoke, blowing snow, and fog can reduce visibility without a normal cloud base.
• METAR/TAF cloud heights are AGL.
• GFA and PIREP cloud heights are normally ASL unless marked AGL.
• Small temperature-dew point spread = fog/low cloud risk.
• Surface cooling overnight favours radiation fog and low stratus.
• Moist upslope flow favours low cloud and poor visibility.

Wind.

• Wind = air moving from higher pressure toward lower pressure.
• Wind is named for the direction it comes from.
• A 270° wind blows from the west toward the east.
• Pressure gradient force starts the wind.
• Strong pressure gradient = strong wind.
• Widely spaced isobars = lighter wind.
• Closely spaced isobars = stronger wind.
• Coriolis force turns moving air: right in the Northern Hemisphere.
• Friction slows surface wind and makes it cross isobars more toward low pressure.
• Around lows in the Northern Hemisphere, wind flows counterclockwise and inward.
• Around highs in the Northern Hemisphere, wind flows clockwise and outward.
• Surface friction usually makes wind lighter and more backed than wind aloft.
• With height, wind often veers and increases as friction decreases.
• Gusts = rapid wind speed fluctuations.
• Wind shear = change in wind speed and/or direction over a short distance.
• LLWS = low-level wind shear; serious takeoff/approach hazard.
• Headwind reduces groundspeed but improves takeoff/landing performance.
• Tailwind increases groundspeed but increases takeoff/landing distance.
• Crosswind affects runway selection and aircraft control.
• Wind over terrain can create mechanical turbulence, mountain wave, updrafts, and downdrafts.
• METAR wind direction is true; landing/takeoff wind is normally magnetic, except true in the NDA.

Air masses.

• Air mass = huge body of air with similar temperature and moisture.
• Air masses get their traits from their source region.
• Source region = where the air mass forms.
• Continental air = dry.
• Maritime air = moist.
• Arctic air = very cold.
• Polar air = cold.
• Tropical air = warm.
• cA = continental Arctic: very cold and dry.
• cP = continental Polar: cold and dry.
• mP = maritime Polar: cool/cold and moist.
• mT = maritime Tropical: warm and moist.
• cT = continental Tropical: hot and dry.
• Air masses are modified as they move over warmer, colder, wetter, or drier surfaces.
• Warm air moving over cold ground/water becomes more stable.
• Cold air moving over warm ground/water becomes more unstable.
• Moist unstable air can produce cumulus, showers, turbulence, and thunderstorms.
• Moist stable air can produce stratus, fog, drizzle, poor visibility, and icing.
• Fronts form where different air masses meet.
• IFR trap: the same air mass can change character after travelling over a new surface.

Fronts: types and associated weather.

• Front = boundary between two different air masses.
• Fronts concentrate weather because temperature, moisture, pressure, and wind change quickly there.
• Cold front = cold air advancing and lifting warm air.
• Cold fronts usually move faster than warm fronts.
• Cold front weather is often narrow, sharp, and intense.
• Cold front signs: abrupt wind shift, temperature drop, pressure rise after passage.
• Cold front hazards: showers, thunderstorms, turbulence, wind shear, icing, squalls.
• Warm front = warm air advancing over colder air.
• Warm front weather is often widespread and gradual.
• Warm front signs: falling pressure ahead, rising temperature after passage, layered cloud sequence.
• Warm front hazards: low stratus, fog, steady precipitation, poor visibility, icing, freezing rain.
• Stationary front = front with little movement.
• Stationary front weather can linger for days: cloud, precipitation, fog, and poor visibility.
• Occluded front = cold front catches up to warm front.
• Occlusion usually means a mature low-pressure system.
• Occluded fronts can bring widespread cloud, precipitation, turbulence, icing, and mixed weather.
• Trough = elongated low-pressure area; often linked with cloud, wind shifts, showers, or thunderstorms.
• Frontogenesis = front becoming stronger.
• Frontolysis = front weakening.
• IFR trap: warm fronts often create worse widespread IFR; cold fronts often create sharper convective hazards.

2.2 Icing

Formation and meteorological factors.

• Icing needs visible moisture plus freezing temperature.
• Main recipe: supercooled liquid water + aircraft surface at or below 0°C.
• Supercooled droplets are liquid below 0°C and freeze on impact.
• Visible moisture includes cloud, fog, rain, drizzle, freezing rain, and freezing drizzle.
• Icing is most common from 0°C to about -20°C.
• Greatest icing threat is often near 0°C to -15°C where liquid water content can be high.
• Very cold clouds often contain more ice crystals and less liquid water, so icing risk may reduce.
• Frontal lift creates widespread icing zones.
• Warm fronts are classic icing traps because warm moist air rides over cold air.
• Freezing rain/drizzle = large-droplet icing threat.
• Freezing rain/drizzle can create rapid clear ice and severe performance loss.
• Stratiform cloud usually gives widespread rime or mixed icing.
• Cumuliform cloud can give stronger, bumpier, more intense icing due to vertical motion.
• Orographic lift can create icing over mountains and windward slopes.
• Icing is more likely near cloud tops where supercooled liquid water can be concentrated.
• Temperature inversions can support freezing rain: warm layer above, cold layer below.
• PIREPs are especially valuable because icing is local and time-sensitive.
• Icing forecast does not guarantee icing, and no forecast does not guarantee no icing.

Types and intensities.

• Icing type = what the ice looks like and how it forms.
• Icing intensity = how fast it is accumulating and how hazardous it is.
• Main icing types: rime, clear, and mixed.
• Rime ice = rough, milky, opaque ice.
• Rime forms when small supercooled droplets freeze almost instantly on impact.
• Clear ice = glossy, clear, or translucent ice.
• Clear ice forms when large supercooled droplets freeze more slowly and spread before freezing.
• Mixed ice = rime and clear ice occurring together.
• Freezing rain/drizzle usually creates dangerous clear or mixed ice.
• Clear ice is often heavier, harder to remove, and more dangerous than rime.
• Rime is easier to recognize but still hazardous.
• Icing intensity levels: trace, light, moderate, severe.
• Trace = perceptible ice, not hazardous unless prolonged.
• Light = may become a problem if flight continues for over 1 hour.
• Moderate = short encounter can become hazardous; de-ice/anti-ice or diversion needed.
• Severe = de-ice/anti-ice equipment cannot control the hazard; immediate diversion needed.
• Report icing to ATS with type, intensity, altitude, location, time, aircraft type, and indicated airspeed.
• IFR exam trap: intensity is about accumulation hazard, not just how ugly the ice looks.

Effects on aircraft performance.

• Icing destroys performance before it looks dramatic.
• Ice changes the airfoil shape.
• Ice disrupts smooth airflow over wings and tail surfaces.
• Lift decreases.
• Drag increases.
• Weight increases.
• Stall speed increases.
• Stall angle of attack decreases.
• Aircraft may stall earlier and at a higher indicated airspeed.
• Climb performance decreases.
• Cruise speed decreases.
• Fuel burn increases because more power is needed.
• Propeller efficiency can decrease.
• Engine thrust can decrease if airflow is disturbed or ice is ingested.
• Jet engine ice ingestion may cause compressor stall or flameout.
• Control surfaces may become restricted or abnormal.
• Tailplane icing can cause dangerous pitch-control problems.
• Windshield or canopy ice can reduce or block forward visibility.
• Antennas and sensors can be affected by ice accumulation.
• De-icing/anti-icing equipment buys time; it does not make icing safe to ignore.
• Severe icing means equipment cannot control the hazard; escape/diversion is required.

Flight precautions and avoidance.

• Best icing strategy = avoid, exit, report.
• Never launch with frost, ice, or snow on critical surfaces.
• Clean aircraft concept = wings, tail, controls, rotors, propellers, and stabilizing surfaces must be clean.
• Check freezing level before departure.
• Check cloud bases, tops, and temperature profile.
• Check GFA icing, turbulence, and freezing level chart.
• Check SIGMETs, AIRMETs, METARs, TAFs, and PIREPs.
• PIREPs are gold because icing is local and time-sensitive.
• Visible moisture near/below freezing = icing threat.
• Avoid freezing rain and freezing drizzle.
• Freezing rain/drizzle can create rapid clear ice or large-droplet icing.
• Plan an escape route before entering cloud in icing conditions.
• Escape options: climb, descend, turn around, or divert depending on temperature, terrain, cloud tops, and clearance.
• If icing is encountered and hazardous, tell ATS and request a new altitude or routing.
• Use de-icing/anti-icing equipment early and according to the AFM/POH.
• De-icing equipment is not a licence to remain in icing.
• Severe icing = equipment cannot control accumulation; immediate diversion/exit required.
• Maintain extra performance margin; icing raises stall speed and reduces climb.
• Be cautious with flap changes if tailplane icing is suspected.
• Avoid prolonged flight in even light icing.
• If aircraft is not approved/equipped for known icing, avoid forecast or reported icing along the route.

2.3 Turbulence

Mechanical turbulence.

• Mechanical turbulence = wind disturbed by terrain, buildings, trees, hangars, or rough surface features.
• It is caused by friction and obstruction of airflow near the surface.
• Stronger wind = stronger mechanical turbulence.
• Rougher terrain = stronger turbulence.
• Mechanical turbulence is usually worst on the leeward side of obstacles.
• Low-level flight near hills, buildings, or tree lines can be bumpy even in clear weather.
• Wind flowing over ridges can create eddies, rotors, downdrafts, and mountain wave.
• Mechanical turbulence is most important during takeoff, approach, landing, and low-level IFR.
• Gusty surface winds often signal mechanical mixing near the ground.
• Stable air can make mechanical turbulence sharper and more trapped near the surface.
• Unstable air can mix turbulence through a deeper layer.
• Wind shear may accompany mechanical turbulence near terrain or obstacles.
• Expect turbulence downwind of buildings, hills, cliffs, tree lines, and mountain ridges.
• Larger obstacles disturb airflow farther downwind.
• Terrain-induced turbulence can exist without cloud or precipitation.
• Avoid flying close behind or below ridges when strong wind crosses the terrain.
• For IFR, mechanical turbulence can make altitude, heading, and airspeed control harder.

Thermal turbulence.

• Thermal turbulence = turbulence caused by rising warm air.
• Surface heating creates convective currents.
• Warm air rises; cooler air sinks to replace it.
• Stronger surface heating = stronger thermal turbulence.
• Thermal turbulence is common on sunny afternoons over land.
• It is usually weaker in the morning, evening, and at night.
• Dark surfaces, dry soil, pavement, rocks, and cities heat quickly and create stronger thermals.
• Water, snow, forests, and moist ground usually heat more slowly and create weaker thermals.
• Thermal turbulence is linked with unstable air.
• Cumulus clouds often mark rising thermal currents.
• Bumpy air below cumulus bases is common.
• Thermal turbulence usually decreases above the convective layer.
• It can cause altitude, airspeed, and attitude fluctuations.
• It can make approaches unstable on hot afternoons.
• It can combine with mechanical turbulence near rough terrain.
• It can combine with frontal or thunderstorm turbulence when unstable moist air is present.
• IFR trap: clear skies do not guarantee smooth air if strong surface heating is active.

Frontal Turbulence

• Frontal turbulence = turbulence caused by air moving and lifting along a front.
• Front = boundary between different air masses.
• Frontal zones often have sharp changes in wind, temperature, pressure, and moisture.
• Wind shift across a front can create wind shear.
• Stronger temperature contrast = stronger frontal lift and turbulence potential.
• Faster-moving front = greater turbulence risk.
• Cold fronts usually produce the strongest frontal turbulence.
• Cold front turbulence is often narrow, sharp, gusty, and convective.
• Cold fronts can produce towering cumulus, CB, showers, squalls, and thunderstorms.
• Warm fronts usually produce broader, smoother, more widespread weather.
• Warm front turbulence is usually less violent but can occur in cloud, precipitation, and icing layers.
• Occluded fronts can produce complex turbulence because multiple air masses are involved.
• Embedded thunderstorms near fronts are a major IFR hazard.
• Frontal turbulence often comes with icing, wind shear, poor visibility, and precipitation.
• Turbulence is commonly worse near the frontal surface and inside/near convective cloud.
• Avoid embedded CBs and strong frontal bands when possible.
• IFR trap: the front itself is not just a line on the chart; it is a zone of active weather.

Wind shear.

• Wind shear = rapid change in wind speed and/or direction over a short distance.
• It can be horizontal, vertical, or both.
• LLWS = low-level wind shear.
• LLWS is most dangerous during takeoff, approach, and landing.
• Wind shear can cause sudden airspeed, altitude, attitude, and flight path changes.
• Headwind suddenly decreases = airspeed loss and sink risk.
• Tailwind suddenly increases = airspeed loss and sink risk.
• Tailwind changing to headwind may give temporary airspeed gain.
• Microburst sequence memory: headwind gain, downdraft, tailwind loss.
• Thunderstorms and CBs are major wind shear sources.
• Gust fronts can create strong wind shear ahead of thunderstorms.
• Frontal zones can create wind shear because wind changes across the air-mass boundary.
• Temperature inversions can create low-level wind shear by trapping different wind layers.
• Terrain and obstacles can create local wind shear and mechanical turbulence.
• Jet streams can create high-level wind shear and clear air turbulence.
• If unsafe wind shear is encountered on approach, execute missed approach/go-around as appropriate.
• Avoid known or suspected microbursts and thunderstorm outflows.
• Report wind shear with airspeed gain/loss, altitude, location, time, and aircraft effect.

Flight precautions.

• Best turbulence strategy = forecast, avoid, slow, secure, report.
• Check GFA turbulence areas, bases, tops, and intensity.
• Check SIGMETs, AIRMETs, PIREPs, METARs, TAFs, and upper winds.
• PIREPs matter because turbulence is local and time-sensitive.
• Avoid thunderstorms, CBs, squall lines, and embedded convective cells.
• Avoid known or suspected severe turbulence.
• Avoid strong wind over mountains if mountain wave/rotor is likely.
• Expect turbulence near fronts, jet streams, terrain, inversions, and strong wind shear.
• Slow to the AFM/POH turbulence penetration or rough-air speed before entering turbulence.
• If no specific speed is published, use an appropriate manoeuvring/rough-air speed from the aircraft guidance.
• Do not chase airspeed and altitude aggressively in turbulence.
• Maintain aircraft attitude and accept reasonable altitude/airspeed fluctuations.
• Avoid abrupt control inputs.
• Keep wings level and maintain control first.
• Secure loose objects and ensure seat belts are fastened.
• In turbulence, use autopilot only if approved and appropriate; disconnect if it is over-controlling.
• In moderate or severe turbulence, consider altitude change, course change, holding, delay, or diversion.
• LLWS or wind shear near the ground = go-around/missed approach if safety is affected.
• Report turbulence intensity, altitude, location, time, and aircraft type to ATS.

2.4 Thunderstorms

Conditions for development.

• Thunderstorm recipe = moisture + instability + lift.
• Moisture supplies the water vapour for cloud, rain, hail, and latent heat release.
• Instability lets lifted air keep rising.
• Lift starts the rising motion.
• Main lifting triggers: surface heating, fronts, terrain, convergence, troughs, and low pressure.
• Warm moist air near the surface increases thunderstorm potential.
• Cold air aloft over warm moist surface air increases instability.
• Strong lapse rate = air cools quickly with height = more unstable.
• Cumulus cloud growth is the early visual clue.
• Towering cumulus means stronger vertical development.
• Cumulonimbus means thunderstorm stage.
• Latent heat release helps the storm grow once condensation begins.
• Wind shear is not required for every thunderstorm, but it helps storms organize and become severe.
• Frontal thunderstorms often form along cold fronts, warm fronts, occlusions, or troughs.
• Air-mass thunderstorms often form from daytime heating in moist unstable air.
• Orographic thunderstorms form when terrain forces moist unstable air upward.
• Embedded thunderstorms are dangerous because cloud can hide CB visually.
• IFR trap: no lightning yet does not mean no thunderstorm threat if towering cumulus is building.

Structure.

• Thunderstorm structure = vertical engine plus hazard zones.
• Main stages: cumulus, mature, dissipating.
• Cumulus stage = building stage with mainly updrafts.
• Mature stage = updrafts and downdrafts together; maximum hazard.
• Dissipating stage = mainly downdrafts; storm weakens but remains hazardous.
• Updraft = rising warm moist air feeding storm growth.
• Downdraft = sinking air, precipitation drag, and cold outflow.
• Cloud base is where rising air first becomes saturated.
• Towering cumulus shows strong vertical development.
• Cumulonimbus means thunderstorm cloud.
• Anvil forms near the top when rising air spreads outward at upper levels.
• Precipitation core contains heavy rain, hail risk, severe turbulence, and possible water ingestion risk.
• Gust front = leading edge of thunderstorm outflow near the surface.
• Outflow can produce sudden wind shift, low-level turbulence, and wind shear.
• Microbursts come from intense downdrafts spreading outward near the surface.
• Lightning, hail, icing, turbulence, and wind shear can exist outside the most visible part of the cloud.
• Embedded CB is dangerous because cloud can hide the storm structure visually.
• IFR trap: the visible CB is only part of the hazardous system.

Classification.

• Thunderstorms can be classified by how they form, how they are organized, and how visible they are to pilots.
• Air-mass thunderstorms form inside a warm, moist, unstable air mass.
• Air-mass thunderstorms are often caused by daytime surface heating.
• Air-mass thunderstorms are usually scattered, local, and short-lived.
• Air-mass thunderstorms often develop in the afternoon and weaken after sunset.
• Frontal thunderstorms form along or near fronts.
• Cold fronts often produce stronger, sharper, more organized thunderstorms.
• Warm fronts can produce widespread cloud with embedded thunderstorms.
• Squall lines are organized lines of thunderstorms.
• Squall lines often form ahead of or along cold fronts.
• Squall lines can move fast and produce severe turbulence, hail, heavy rain, lightning, and wind shear.
• Embedded thunderstorms are hidden inside other cloud layers.
• Embedded thunderstorms are especially dangerous in IFR because visual avoidance may be impossible.
• Orographic thunderstorms form when terrain lifts moist unstable air.
• Severe thunderstorms are operationally important because hazards extend outside the visible cloud.
• Thunderstorm appearance does not reliably tell you how bad turbulence or hail is inside.
• IFR trap: a thunderstorm can be dangerous whether it is air-mass, frontal, embedded, or squall-line.

Hazards: macrobursts and microbursts.

• Downburst = strong downdraft that hits the surface and spreads outward.
• Microburst = small, intense downburst.
• Macroburst = larger downburst affecting a wider area.
• Both create dangerous low-level wind shear.
• Greatest danger is during takeoff, approach, and landing.
• Microburst sequence: headwind gain, downdraft, tailwind loss.
• Initial headwind gain can make performance look better for a moment.
• Downdraft then forces the aircraft downward.
• Tailwind loss reduces airspeed and climb performance.
• The aircraft may sink rapidly even with high power.
• Microbursts are short-lived but extremely intense.
• Macrobursts last longer and cover a larger area than microbursts.
• Wet microburst = heavy rain reaches the surface.
• Dry microburst = precipitation evaporates before reaching the ground; virga may be the clue.
• Gust fronts and outflow boundaries can arrive before the thunderstorm itself.
• Avoid takeoff or landing when thunderstorms or wind shear are near the airport.
• Heed LLWS alerts, PIREPs, wind shear warnings, and thunderstorm outflow signs.
• IFR trap: an airspeed increase on final may be the first part of a microburst, not a good sign.

Squall lines.

• Squall line = organized line of thunderstorms.
• Usually forms ahead of or along a cold front.
• Can also form along troughs or convergence zones.
• Squall lines can extend over very long distances.
• They often move quickly and can arrive earlier than expected.
• Hazards include severe turbulence, hail, lightning, heavy rain, icing, wind shear, and low visibility.
• Gust fronts can occur ahead of the visible storm line.
• Gust front = leading edge of thunderstorm outflow.
• Gust fronts can cause sudden wind shifts and low-level wind shear.
• Squall lines may contain embedded CBs hidden by cloud or precipitation.
• Radar often shows a narrow band of strong precipitation returns.
• Strong radar returns usually mean greater convective hazard.
• Do not try to pick through small gaps in an active squall line.
• Gaps can close quickly and may still contain severe turbulence.
• Best options: delay, divert, land before the line arrives, or route well around it.
• IFR trap: a squall line is not just bad visibility; it is an organized wall of convective hazards.

Flight precautions.

• Best thunderstorm precaution = avoid, don’t penetrate.
• Never treat a thunderstorm as light just because radar returns look light.
• Thunderstorms can contain turbulence, hail, icing, lightning, heavy rain, wind shear, microbursts, low ceilings, and poor visibility.
• Do not take off or land when a thunderstorm is approaching.
• Gust fronts can arrive before the visible storm or rain.
• Do not fly under a thunderstorm, even if you can see through to the other side.
• Avoid severe thunderstorms and intense radar returns by at least 20 NM.
• Include the anvil of large CBs in the avoidance area.
• Do not try to pick through embedded thunderstorms in IMC.
• Avoid areas where thunderstorms cover 5/8 or more of the area.
• If topping a storm, clear the top by at least 1,000 ft for each 10 kt of wind at cloud top.
• Use weather radar carefully; radar mainly shows precipitation, not all turbulence or wind shear.
• Check SIGMETs, AIRMETs, GFA, radar, satellite, lightning, METARs, TAFs, and PIREPs.
• Delay, divert, land early, or route well around convective weather.
• If unavoidable, tighten belts, secure loose items, set turbulence penetration speed, and fly instruments.
• In thunderstorm penetration, maintain attitude and avoid chasing altitude aggressively.
• Do not make abrupt control inputs.
• If wind shear or microburst is encountered on approach, go around or execute missed approach if safety is affected.
• Report thunderstorms, turbulence, icing, wind shear, and severe weather to ATS.

2.5 Aviation Weather Reports

Types and times: METAR, SPECI, METAR AUTO, SPECI AUTO.

• Best thunderstorm precaution = avoid, don’t penetrate.
• Never treat a thunderstorm as light just because radar returns look light.
• Thunderstorms can contain turbulence, hail, icing, lightning, heavy rain, wind shear, microbursts, low ceilings, and poor visibility.
• Do not take off or land when a thunderstorm is approaching.
• Gust fronts can arrive before the visible storm or rain.
• Do not fly under a thunderstorm, even if you can see through to the other side.
• Avoid severe thunderstorms and intense radar returns by at least 20 NM.
• Include the anvil of large CBs in the avoidance area.
• Do not try to pick through embedded thunderstorms in IMC.
• Avoid areas where thunderstorms cover 5/8 or more of the area.
• If topping a storm, clear the top by at least 1,000 ft for each 10 kt of wind at cloud top.
• Use weather radar carefully; radar mainly shows precipitation, not all turbulence or wind shear.
• Check SIGMETs, AIRMETs, GFA, radar, satellite, lightning, METARs, TAFs, and PIREPs.
• Delay, divert, land early, or route well around convective weather.
• If unavoidable, tighten belts, secure loose items, set turbulence penetration speed, and fly instruments.
• In thunderstorm penetration, maintain attitude and avoid chasing altitude aggressively.
• Do not make abrupt control inputs.
• If wind shear or microburst is encountered on approach, go around or execute missed approach if safety is affected.
• Report thunderstorms, turbulence, icing, wind shear, and severe weather to ATS.

Decoding.

• Decode METAR left to right.
• METAR/SPECI = actual observed aerodrome weather.
• First group = report type: METAR or SPECI.
• Second group = station identifier, usually four-letter ICAO code in Canada.
• Date/time group = day of month and UTC time, ending in Z.
• AUTO = automated observation.
• CCA, CCB, etc. = corrected report.
• Wind group = direction true, speed in knots, gusts if reported.
• 00000KT = calm wind.
• VRB means variable wind direction.
• Visibility in Canadian METARs is normally in statute miles.
• RVR = runway visual range, usually shown as R runway / value in feet.
• Present weather uses intensity, descriptor, precipitation/obscuration codes.
• -RA = light rain; RA = moderate rain; +RA = heavy rain.
• BR = mist; FG = fog; SN = snow; TS = thunderstorm; FZ = freezing.
• Cloud groups show amount and height in hundreds of feet AGL.
• FEW and SCT are not ceilings.
• BKN and OVC are ceilings.
• Temperature/dew point are in Celsius.
• M before temperature means minus.
• Altimeter setting in Canada is usually A followed by inches of mercury.
• RMK = remarks, often cloud types and extra visibility/weather details.
• SLP = sea level pressure in remarks.
• Read the newest METAR/SPECI first, then compare with TAF, GFA, SIGMET/AIRMET, and PIREPs.

Pilot report (PIREP).

• PIREP = pilot report of actual weather encountered in flight.
• PIREPs are real-time, local, and pilot-observed.
• PIREP designator = UA.
• Urgent PIREP designator = UUA.
• PIREPs are issued as reported, not on a fixed schedule.
• PIREPs help other pilots, ATS, and weather forecasters.
• PIREPs are especially valuable for icing, turbulence, wind shear, cloud tops, cloud bases, and thunderstorms.
• Forecasts are broad; PIREPs are actual conditions at a place, altitude, and time.
• A PIREP should include location, time, altitude, aircraft type, and the weather observed.
• Report icing with intensity, type, altitude, location, time, aircraft type, and indicated airspeed if useful.
• Report turbulence with intensity, altitude, location, time, cloud association, aircraft type, and duration if useful.
• Report wind shear with airspeed gain/loss, altitude, location, and aircraft effect.
• Report cloud tops/bases, visibility, precipitation, thunderstorms, volcanic ash, and unusual weather.
• Urgent PIREPs are for hazards that need quick distribution.
• Moderate or greater icing/turbulence, wind shear, severe weather, or volcanic ash should be reported urgently.
• PIREPs can confirm, improve, or trigger updates to forecasts and warnings.
• INRAT trap: no PIREP does not mean no hazard; it may mean nobody reported it.

2.6 Aviation Forecasts

Times issued and validity.

• All aviation forecast times are UTC/Zulu.
• Always check issue time, valid time, and expiry/replacement time.
• GFA = big-picture area forecast for at or below 24,000 ft.
• GFA is issued about 30 min before the forecast period.
• GFA valid times: 0000Z, 0600Z, 1200Z, 1800Z.
• GFA issue times are approximately 2330Z, 0530Z, 1130Z, 1730Z.
• Each new GFA set replaces the previous set.
• Each GFA issue gives charts for start time, +6 hr, and +12 hr.
• Final GFA clouds/weather chart includes an IFR outlook for an additional 12 hr.
• TAF = aerodrome forecast.
• TAFs are generally issued every 6 hr.
• TAF validity may be up to 30 hr.
• TAF issue/update periods may vary; check the CFS.
• The next TAF issue time is stated at the end of each TAF.
• TAF AMD = amended forecast when the forecast is no longer representative.
• AIRMET = moderate/widespread weather advisory that amends the relevant GFA.
• AIRMET validity is normally 4 hr.
• SIGMET = significant weather warning for hazards affecting safety.
• SIGMET validity is normally 4 hr.
• Volcanic ash and tropical cyclone SIGMETs are normally valid for 6 hr.
• Upper wind/temperature forecasts use fixed issue and validity blocks; read the product header carefully.
• A forecast may be valid but still outdated if a newer amendment, SIGMET, AIRMET, METAR, SPECI, or PIREP changes the picture.

Decoding.

• Decode aviation forecasts by product first: TAF, GFA, FD/FB, SIGMET, AIRMET.
• TAF = aerodrome forecast; GFA = regional forecast map; FD/FB = upper winds and temperatures; SIGMET/AIRMET = hazard message.
• All aviation forecast times are UTC/Zulu.
• TAF decoding is similar to METAR decoding, but it predicts future conditions.
• TAF order: type, station, issue time, validity, wind, visibility, weather, cloud, change groups, remarks.
• TAF AMD = amended forecast.
• TAF validity group like 2812/2912 = valid from 28th at 1200Z to 29th at 1200Z.
• TAF wind direction is true.
• TAF visibility is in statute miles; P6SM = greater than 6 SM.
• TAF cloud heights are AGL.
• In Canadian TAFs, CAVOK is not used.
• TAF VC means 5 to 10 NM from the centre of the runway complex.
• FM = rapid permanent change; everything before FM is superseded.
• BECMG = gradual permanent change, usually over 1 to 2 hr and not more than 4 hr.
• TEMPO = temporary fluctuation; each event less than 1 hr and total time not more than half the period.
• PROB30 or PROB40 = 30% or 40% probability of aviation-significant alternate conditions.
• PROB below 30% is not used; 50% or more should be forecast with FM, BECMG, or TEMPO.
• RMK NXT FCST BY = next TAF issue time.
• GFA title box gives region, chart type, issue time, and valid time.
• GFA has two main charts: clouds/weather and icing/turbulence/freezing level.
• GFA bases/tops are normally ASL unless marked SFC or AGL.
• GFA panels are snapshots; interpolate between valid times.
• FD/FB winds aloft code: first two digits wind direction true, next two digits wind speed.
• FD/FB 9900 = light and variable.
• FD/FB temperatures are Celsius; temperatures above 24,000 ft are assumed negative.
• FD/FB winds 100-199 kt: subtract 50 from direction code and add 100 to speed.
• SIGMET = significant weather affecting safety; AIRMET = moderate/widespread hazard or GFA amendment.
• Decode SIGMET/AIRMET by FIR, phenomenon, validity, location, altitude/level, movement, intensity, and change.

Graphical Area Forecasts (GFA).

• GFA = Graphical Area Forecast.
• GFA gives the big-picture forecast over a region, not just one aerodrome.
• GFA covers forecast weather at or below 24,000 ft.
• GFA is mainly for pre-flight planning in Canada.
• GFA is issued four times daily.
• GFA issue times are approximately 2330Z, 0530Z, 1130Z, and 1730Z.
• GFA valid times are 0000Z, 0600Z, 1200Z, and 1800Z.
• Each new GFA set replaces the previous set.
• Each GFA issue has charts valid at start time, +6 hr, and +12 hr.
• Final clouds/weather chart includes an IFR outlook for an additional 12 hr.
• GFA has two main chart types: CLDS/WX and ICG/TURB/FZLVL.
• CLDS/WX chart shows clouds, weather, visibility, precipitation, fronts, pressure systems, and comments.
• ICG/TURB/FZLVL chart shows icing, turbulence, and freezing level.
• GFA heights are normally ASL unless marked otherwise.
• GFA cloud bases/tops are usually in hundreds of feet.
• GFA visibility is in statute miles.
• GFA winds are in knots.
• GFA times are UTC/Zulu.
• GFA panels are snapshots; interpolate weather movement between valid times.
• AIRMET or SIGMET may amend the current and relevant GFA.
• Use GFA with METAR, SPECI, TAF, PIREP, radar, satellite, lightning, AIRMET, and SIGMET.

Aerodrome Forecasts (TAF).

• TAF = Terminal/Aerodrome Forecast.
• TAF gives forecast weather for a specific aerodrome.
• TAF is a forecast, not an observation.
• TAF describes the most probable weather and timing expected at the aerodrome.
• TAF is mainly for pre-flight and in-flight planning.
• TAF normally applies within about 5 NM of the runway complex.
• Significant weather such as thunderstorms may be included when 5 to 10 NM from the aerodrome.
• TAF requires a regular METAR/SPECI observation program.
• TAF issue time is UTC/Zulu.
• TAFs are issued about 20 min before the validity period.
• TAF validity may be up to 30 hr.
• TAF is valid from issue time until amended, replaced by the next scheduled TAF, or the validity period ends.
• TAF AMD = amended TAF.
• RMK NXT FCST BY gives the next forecast issue time.
• TAF wind direction is true.
• TAF visibility is in statute miles.
• P6SM = visibility greater than 6 SM.
• TAF cloud heights are AGL.
• In Canadian TAFs, CAVOK is not used.
• TAF VC means weather between 5 and 10 NM from the runway complex.
• FM = rapid permanent change; new complete forecast begins.
• BECMG = gradual permanent change.
• TEMPO = temporary fluctuation.
• PROB30/PROB40 = 30% or 40% probability of aviation-significant alternate conditions.
• Use TAF with METAR, SPECI, GFA, AIRMET, SIGMET, PIREP, radar, satellite, and lightning.

Upper-level winds and temperature forecasts (FD).

• TAF = Aerodrome Forecast.
• TAF is forecast weather, not observed weather.
• TAF gives the most probable weather expected at a specific aerodrome.
• TAF is used for pre-flight and in-flight planning.
• TAF normally covers weather within about 5 NM of the runway complex.
• Significant weather such as thunderstorms may be included when 5 to 10 NM from the aerodrome.
• TAFs are generally issued every 6 hr.
• TAFs are issued about 20 min before the validity period.
• TAF validity may be up to 30 hr.
• TAF times are UTC/Zulu.
• TAF wind direction is true.
• TAF visibility is in statute miles.
• TAF cloud heights are AGL.
• TAF AMD = amended forecast.
• TAF is valid from issue time until amended, replaced by the next TAF, or expired.
• RMK NXT FCST BY gives the next forecast issue time.
• FM = rapid permanent change and starts a new complete forecast period.
• BECMG = gradual permanent change.
• TEMPO = temporary fluctuation.
• PROB30/PROB40 = 30% or 40% probability of aviation-significant alternate conditions.
• CAVOK is not used in Canadian TAFs.
• Use TAF with METAR, SPECI, GFA, PIREP, AIRMET, SIGMET, radar, satellite, and lightning.

Significant In-Flight Weather Warning Messages (SIGMET).

• SIGMET = Significant Meteorological Information.
• SIGMET warns of weather that may affect aircraft safety.
• SIGMET is for significant or severe in-flight weather hazards.
• SIGMET may describe weather that is occurring or expected to occur.
• SIGMET is not a routine forecast like a TAF.
• SIGMET is a warning/advisory message for hazardous weather in a FIR.
• SIGMET gives the hazard, location, altitude or flight levels, movement, intensity/change, and validity period.
• Normal SIGMET validity is 4 hr.
• Volcanic ash and tropical cyclone SIGMETs are normally valid for 6 hr.
• SIGMET can be issued before the phenomenon begins.
• SIGMETs may amend the current and relevant GFA.
• WSCN = normal Canadian SIGMET header.
• WVCN = volcanic ash SIGMET header.
• WCCN = tropical cyclone SIGMET header.
• SIGMET hazards include severe turbulence, severe icing, thunderstorms, squall lines, volcanic ash, tropical cyclones, and other significant weather.
• Decode SIGMET by reading: FIR, sequence, validity, phenomenon, location, level, movement, and intensity trend.
• SIGMET always outranks a calm-looking forecast picture.
• IFR trap: a valid TAF or GFA does not cancel a SIGMET.

2.7 Weather Maps and Prognostic Charts

Surface weather chart.

• Surface weather chart = analyzed current weather map, not a forecast.
• It shows the pressure pattern at mean sea level.
• It shows surface highs, lows, fronts, troughs, precipitation, and obstructions to visibility.
• Observation times are 0000Z, 0600Z, 1200Z, and 1800Z.
• It is usually issued 2 to 3 hr after observation time.
• Always check the chart time before using it.
• Weather moves; the chart is only a snapshot.
• Use the surface chart with METAR, SPECI, TAF, GFA, SIGMET, AIRMET, radar, satellite, and PIREPs.
• Isobars connect equal pressure.
• Tight isobars = strong pressure gradient = stronger winds.
• Wide isobars = weaker pressure gradient = lighter winds.
• Low pressure usually means rising air, cloud, precipitation, and unsettled weather.
• High pressure usually means sinking air and more stable weather, but may also trap fog, haze, or low stratus.
• Cold fronts often bring sharper weather changes and convective weather.
• Warm fronts often bring widespread cloud, precipitation, and lower ceilings ahead of the front.
• Occluded fronts combine warm-front and cold-front weather features.
• Stationary fronts can keep poor weather stuck over an area.
• Surface pressure patterns can be treated as representative up to about 3,000 ft.
• IFR use: identify route-wide systems, frontal crossings, pressure gradients, and likely ceiling/visibility trouble.

Upper-level analysis charts to 700 MB.

• ANAL = analysis, not forecast.
• Upper-level analysis charts show observed/analyzed atmospheric conditions aloft.
• In aviation weather charts, hPa is used; 1 hPa = 1 mb.
• To 700 mb usually means low/mid-level upper-air charts such as 850 hPa and 700 hPa.
• 850 hPa is approximately 5,000 ft.
• 700 hPa is approximately 10,000 ft.
• Upper-level analysis charts are normally based on 0000Z and 1200Z observations.
• They are usually issued more than 3 hr after observation time.
• They show wind speed, wind direction, temperature, and moisture at pressure levels.
• Pressure-level charts are not constant-altitude charts; they are constant-pressure surfaces.
• Height contours show the altitude of that pressure surface.
• Tight height contours usually mean stronger winds aloft.
• Winds aloft generally flow roughly parallel to height contours, especially away from surface friction.
• Troughs aloft often support rising air, cloud, precipitation, turbulence, and unsettled weather.
• Ridges aloft often support sinking air and more stable weather.
• 850 hPa is useful for low-level wind, temperature advection, frontal structure, and low-level moisture.
• 700 hPa is useful for mid-level moisture, lift, cloud development, and icing clues.
• Use upper-level analysis with surface charts, GFA, TAF, METAR/SPECI, PIREPs, SIGMETs, and AIRMETs.
• IFR trap: upper-level analysis helps explain the weather system, but it is not a stand-alone go/no-go product.

Prognostic surface chart.

• Prognostic surface chart = forecast surface weather map.
• PROG means prognosis or prognostic.
• It is a forecast, not an observation or analysis.
• It predicts future positions of surface highs, lows, fronts, troughs, ridges, and precipitation areas.
• Use it to see where the weather systems are expected to move.
• Always check the valid time, not just the issue time.
• Compare the PROG chart with the latest surface analysis chart to see how systems are moving.
• High pressure usually suggests sinking/stable air, but fog, haze, inversions, or low stratus can still occur.
• Low pressure usually suggests rising/unsettled air, cloud, precipitation, and lower ceilings/visibility.
• Tight isobars or close pressure patterns suggest stronger surface winds.
• Cold fronts often mean sharper weather changes, wind shifts, showers, turbulence, and possible thunderstorms.
• Warm fronts often mean widespread layered cloud, precipitation, reduced visibility, and lower ceilings ahead of the front.
• Occluded fronts can combine cold-front and warm-front weather features.
• Stationary fronts can keep poor weather over the same area for a long time.
• Troughs can focus cloud, precipitation, wind shifts, and instability.
• Ridges usually point to more stable weather behind systems.
• IFR use: plan route timing around forecast frontal passages, lows, precipitation shields, and pressure gradients.
• A PROG chart is broad-scale; it does not replace METAR, SPECI, TAF, GFA, SIGMET, AIRMET, radar, satellite, or PIREPs.

Significant weather prognostic chart from 700 to 400 MB.

• Significant weather prognostic chart = forecast hazard chart.
• PROG = forecast, not analysis.
• 700 to 400 mb/hPa = mid-level SIGWX chart.
• 700 to 400 hPa is roughly FL100 to FL240.
• It shows weather hazards that matter to aircraft enroute.
• It is not an airport-specific ceiling/visibility forecast.
• Main hazards: CB/thunderstorms, turbulence, mountain waves, icing, significant cloud layers, and freezing level.
• Moderate to severe icing is depicted; light icing is not.
• Significant cloud layers may show bases and tops.
• Freezing level line = 0°C height, usually at 5,000-ft intervals.
• Freezing level labels are in hundreds of feet.
• Surface highs, lows, fronts, and troughs may be shown with movement direction and speed in knots.
• CB implies hail, moderate or greater turbulence, and icing.
• ISOL = isolated; OCNL = occasional; FRQ = frequent.
• CAT = clear air turbulence.
• LEE WV = lee wave or mountain wave.
• FZLVL = freezing level.
• Always check chart valid time, level band, and latest SIGMET/AIRMET updates.

Times issued and validity.

• All chart times are UTC/Zulu.
• Always check whether the chart is ANAL or PROG.
• ANAL = analysis of observed weather.
• PROG = forecast chart for a future valid time.
• Surface weather chart observation times are 0000Z, 0600Z, 1200Z, and 1800Z.
• Surface weather chart is usually issued 2 to 3 hr after observation.
• Surface weather chart is an analysis, not a forecast.
• Upper-level analysis charts are based on 0000Z and 1200Z observations.
• Upper-level analysis charts are usually issued more than 3 hr after observation.
• Upper-level analysis charts include standard levels such as 850 hPa, 700 hPa, 500 hPa, and 250 hPa.
• Upper-level forecast chart PROG is prepared about 12 hr before valid time.
• Upper-level forecast chart valid times are 0000Z, 0600Z, 1200Z, and 1800Z.
• Upper-level forecast chart levels include FL240, FL340, FL390, and FL450.
• Significant weather forecast/prognostic chart PROG is prepared about 12 hr before valid time.
• Significant weather forecast/prognostic chart valid times are 0000Z, 0600Z, 1200Z, and 1800Z.
• Significant weather forecast/prognostic chart level bands include FL100-FL240 and FL250-FL630.
• A chart can be valid but not the newest available product.
• Use charts with METAR, SPECI, TAF, GFA, PIREP, AIRMET, SIGMET, radar, and satellite.

Symbols and decoding.

• Start decoding by identifying the chart type: surface, upper ANAL, upper PROG, or SIGWX PROG.
• Check the valid time before reading the weather picture.
• Check the level band: surface, 850 hPa, 700 hPa, 700-400 hPa, FL100-FL240, or FL250-FL630.
• ANAL means analysis of observed weather.
• PROG means forecast weather.
• H means high pressure; L means low pressure.
• Isobars are lines of equal mean sea-level pressure.
• Tight isobars mean stronger pressure gradient and stronger winds.
• Front symbols show air-mass boundaries and likely weather change zones.
• Cold fronts often bring sharper weather changes, wind shift, showers, turbulence, and possible CB.
• Warm fronts often bring layered cloud, precipitation, lower ceilings, and reduced visibility ahead of the front.
• Occluded fronts combine cold-front and warm-front weather features.
• Stationary fronts can keep poor weather over one area.
• Trough lines mark elongated lower-pressure areas and can focus cloud, precipitation, and instability.
• Ridge lines mark elongated higher-pressure areas and often suggest more stable air.
• Movement arrows show direction of motion; speed is usually in knots.
• STNR means stationary or moving less than 5 kt.
• Cloud bases and tops are usually decoded in hundreds of feet.
• On GFA, heights are ASL unless marked AGL.
• CIG and AGL identify ceiling or height above ground level.
• P6SM means visibility greater than 6 statute miles.
• Weather is usually written after visibility, such as 2-4SM -RA BR.
• Dashed or bounded areas show where the written weather applies.
• Scalloped borders enclose organized cloud or significant weather areas.
• CB means cumulonimbus and should trigger thunderstorm hazard thinking.
• CB implies hail, moderate or greater turbulence, and icing.
• ISOL, OCNL, and FRQ describe coverage or frequency, not intensity.
• CAT means clear air turbulence.
• LEE WV or MTW means lee/mountain wave.
• FZLVL means freezing level.
• MX means mixed icing; CLR means clear icing.
• XXX beside a cloud base/top means the layer extends beyond the chart limit.
• Jet stream arrows show direction, speed, and flight level; strong jets can imply turbulence risk.
• Wind barbs show wind direction and speed; read direction as where the wind is from.
• Always cross-check chart symbols with GFA, TAF, METAR/SPECI, SIGMET, AIRMET, PIREP, radar, and satellite.

2.8 Weather Interpretation

Weather systems affecting preferred routes and altitudes.

• Pick the route and altitude that avoid the worst combination of cloud, icing, turbulence, thunderstorms, terrain, and headwind.
• Weather interpretation is not just reading one product; compare surface chart, upper charts, GFA, TAF, METAR/SPECI, PIREP, AIRMET, SIGMET, radar, satellite, and winds aloft.
• Start with the big picture: lows, highs, fronts, troughs, ridges, pressure gradient, freezing level, and upper winds.
• Low pressure usually means rising air, cloud, precipitation, turbulence, and lower ceilings/visibility.
• High pressure usually means sinking/stable air, but can still trap fog, haze, smoke, or low stratus.
• Cold fronts often mean sharper weather changes, wind shift, turbulence, showers, CB, and possible squall lines.
• Warm fronts often mean widespread layered cloud, precipitation, icing risk, lower ceilings, and reduced visibility ahead of the front.
• Occluded fronts can combine cold-front and warm-front hazards.
• Stationary fronts can keep poor weather stuck along a route.
• Troughs focus lift, cloud, precipitation, turbulence, and instability.
• Ridges usually favour more stable weather, but watch for trapped low cloud or fog underneath.
• Tight isobars mean stronger winds; plan for drift, groundspeed, fuel, turbulence, and alternate needs.
• Thunderstorms and CB should be avoided laterally and vertically; do not plan to thread gaps without reliable airborne weather radar.
• Icing route choice depends on freezing level, cloud layers, precipitation type, and escape altitude.
• If icing is forecast in cloud, prefer a route or altitude that stays clear of visible moisture or exits the freezing layer quickly.
• Mountain routes need special attention to wind direction, mountain waves, lee-side turbulence, cloud on ridges, and downdrafts.
• Upper winds can make one altitude faster but rougher; best altitude is not always the strongest tailwind.
• Turbulence may push the preferred altitude lower or higher depending on mountain wave, jet stream, frontal, convective, or mechanical turbulence.
• Low ceilings and visibility may make a lower route unsafe near terrain, even if it looks shorter.
• Route timing matters: a delayed departure may let a front pass, fog lift, or convective activity build.
• A longer route around weather is often safer than a shorter route through hazards.
• Preferred altitude must still meet IFR minimum altitude, terrain clearance, oxygen, aircraft performance, icing equipment, and ATC requirements.
• Always update the plan if reports show the system moving faster, slower, stronger, or weaker than forecast.

3.1 Pitot Static System

Pitot.

• Pitot system supplies ram air pressure to the airspeed indicator.
• Pitot pressure is total pressure: ram pressure plus static pressure.
• The airspeed indicator compares pitot pressure with static pressure.
• More forward speed creates more ram pressure, so indicated airspeed increases.
• The pitot tube normally faces into the relative airflow.
• Pitot heat helps prevent ice blockage in visible moisture or cold conditions.
• Pitot heat should be checked before flight according to aircraft procedures.
• A blocked pitot tube can cause unreliable or false airspeed indications.
• If the pitot opening is blocked but the drain hole remains open, the airspeed indicator usually reads zero.
• If both the pitot opening and drain hole are blocked, trapped pressure makes the airspeed indicator act like an altimeter.
• With pitot and drain blocked, climbing makes indicated airspeed increase falsely.
• With pitot and drain blocked, descending makes indicated airspeed decrease falsely.
• Pitot blockage affects the airspeed indicator only.
• Pitot blockage does not directly affect the altimeter or vertical speed indicator.
• Compare airspeed with pitch, power, attitude, GPS groundspeed, and aircraft performance to identify a suspected pitot problem.
• In icing or heavy precipitation, suspect pitot/static errors early if indications do not match aircraft attitude and power.

Static.

• Static system supplies ambient air pressure to the airspeed indicator, altimeter, and vertical speed indicator.
• Static pressure is outside atmospheric pressure around the aircraft.
• Static ports are usually mounted where airflow disturbance is minimized.
• The altimeter uses static pressure to indicate altitude.
• The vertical speed indicator uses changes in static pressure to show rate of climb or descent.
• The airspeed indicator compares pitot pressure against static pressure.
• If the static source is blocked, all three pitot-static instruments can be affected.
• With static blocked, the altimeter freezes at the altitude where the blockage occurred.
• With static blocked, the VSI usually goes to zero after any trapped pressure stabilizes.
• With static blocked, the ASI reads incorrectly because it is comparing pitot pressure to trapped static pressure.
• With static blocked during a climb, ASI reads lower than actual.
• With static blocked during a descent, ASI reads higher than actual.
• Static blockage can be caused by ice, water, dirt, tape, insects, or port damage.
• Alternate static source supplies static pressure from another location, often inside the cabin.
• Using alternate static can introduce small instrument errors depending on aircraft design.
• In many aircraft, alternate static may make the altimeter read slightly high and the ASI read slightly high.
• Always follow the aircraft POH/AFM for alternate static source use and corrections.

Anti-icing.

• Pitot-static anti-icing prevents ice from blocking pressure sources.
• Pitot heat electrically heats the pitot tube to prevent or remove ice.
• Pitot heat protects the ram-air source for the airspeed indicator.
• Some aircraft also have heated static ports.
• Some aircraft have alternate static sources if the normal static ports become blocked.
• Pitot heat should be used according to the POH/AFM, especially in visible moisture near freezing temperatures.
• Pitot heat should normally be checked during preflight or before takeoff as required by aircraft procedures.
• Do not wait for airspeed errors before thinking about pitot heat in icing conditions.
• Pitot ice can cause unreliable airspeed indications.
• Static port ice can affect the altimeter, VSI, and airspeed indicator.
• If the pitot opening is blocked and the drain hole is open, the ASI usually reads zero.
• If the pitot opening and drain hole are both blocked, the ASI acts like an altimeter.
• If the static system is blocked, the altimeter freezes, the VSI goes to zero, and the ASI gives false readings.
• Pitot heat does not fix a blocked static port unless the aircraft has heated static ports too.
• Alternate static may restore usable static pressure but can introduce instrument errors.
• Always follow POH/AFM procedures for pitot heat, static heat, alternate static, and instrument-failure checks.

Alternate static.

• Alternate static provides a backup source of static pressure if the normal static ports are blocked.
• Static pressure is used by the altimeter, vertical speed indicator, and airspeed indicator.
• Selecting alternate static may restore usable indications after a static-source blockage.
• Alternate static often uses cabin pressure as the backup static source.
• Cabin pressure is usually slightly lower than outside static pressure because of airflow around the aircraft.
• Because alternate static pressure may differ from outside static pressure, instrument readings may have errors.
• In many aircraft, alternate static causes the altimeter to read slightly high.
• In many aircraft, alternate static causes the airspeed indicator to read slightly high.
• The VSI may briefly show a climb when alternate static is selected.
• Exact errors depend on the aircraft and must be taken from the POH/AFM.
• Alternate static helps static-system failures only.
• Alternate static does not fix a blocked pitot tube.
• If the pitot tube is blocked, the airspeed problem remains even with alternate static selected.
• If the normal static source is blocked and no alternate static source exists, some aircraft procedures may allow breaking the VSI glass as an emergency static source.
• Breaking VSI glass is not a normal procedure; use it only if the POH/AFM permits it.
• After selecting alternate static, cross-check pitch, power, GPS groundspeed, and aircraft performance.

Sources and errors.

• Pitot-static instruments depend on two pressure sources: pitot pressure and static pressure.
• Pitot pressure is total pressure: ram pressure plus static pressure.
• Static pressure is ambient outside air pressure.
• The airspeed indicator uses both pitot and static pressure.
• The altimeter uses static pressure only.
• The vertical speed indicator uses static pressure only.
• Pitot source errors mainly affect the airspeed indicator.
• Static source errors affect the airspeed indicator, altimeter, and vertical speed indicator.
• Pitot blockage with drain hole open usually makes the ASI read zero.
• Pitot and drain both blocked makes the ASI act like an altimeter.
• With pitot and drain blocked, ASI falsely increases in a climb.
• With pitot and drain blocked, ASI falsely decreases in a descent.
• Static blockage freezes the altimeter at the altitude where the blockage occurred.
• Static blockage makes the VSI go to zero after pressure stabilizes.
• Static blockage makes ASI read lower than actual in a climb.
• Static blockage makes ASI read higher than actual in a descent.
• Alternate static may restore usable indications after static blockage.
• Alternate static may introduce errors; in many aircraft altitude and airspeed read slightly high.
• Pitot heat protects the pitot source from ice.
• Static heat, if installed, protects static ports from ice.
• Position error occurs when pressure sensed at the pitot or static source is affected by aircraft attitude, configuration, or airflow distortion.
• Instrument error comes from imperfections in the instrument itself.
• Density error explains why indicated airspeed differs from true airspeed as altitude and temperature change.
• Compressibility error becomes more important at higher speeds and higher altitudes.
• Always cross-check pitot-static instruments with pitch, power, attitude, GPS groundspeed, and expected aircraft performance.

3.2 Pitot Static Instruments

Principles.

• Pitot-static instruments use air pressure to indicate speed, altitude, and vertical movement.
• The three main pitot-static instruments are the airspeed indicator, altimeter, and vertical speed indicator.
• The airspeed indicator uses both pitot pressure and static pressure.
• The altimeter uses static pressure only.
• The vertical speed indicator uses static pressure only.
• Pitot pressure is total pressure: ram pressure plus static pressure.
• Static pressure is ambient outside air pressure.
• The airspeed indicator measures the difference between pitot pressure and static pressure.
• As dynamic pressure increases, indicated airspeed increases.
• The altimeter measures static pressure and converts it into altitude.
• As aircraft climbs, static pressure decreases and the altimeter indicates higher altitude.
• As aircraft descends, static pressure increases and the altimeter indicates lower altitude.
• The vertical speed indicator measures the rate of change of static pressure.
• A rapid decrease in static pressure indicates a climb.
• A rapid increase in static pressure indicates a descent.
• Pitot blockage mainly affects the airspeed indicator.
• Static blockage affects the airspeed indicator, altimeter, and vertical speed indicator.
• Pitot-static instruments can be misleading if pressure sources are blocked, iced, leaking, or affected by position error.
• Always cross-check pitot-static indications with attitude, power, GPS groundspeed, and expected aircraft performance.

Errors.

• Pitot-static instrument errors come from blocked pressure sources, leaks, position error, instrument error, density change, temperature change, and lag.
• The airspeed indicator is affected by pitot errors and static errors.
• The altimeter and vertical speed indicator are affected by static errors only.
• Pitot blockage mainly affects the airspeed indicator.
• Static blockage affects the airspeed indicator, altimeter, and vertical speed indicator.
• If the pitot tube is blocked and the drain hole is open, the ASI usually reads zero.
• If the pitot tube and drain hole are blocked, the ASI acts like an altimeter.
• With pitot and drain blocked, ASI falsely increases in a climb.
• With pitot and drain blocked, ASI falsely decreases in a descent.
• With static blocked, the altimeter freezes at the altitude where the blockage occurred.
• With static blocked, the VSI usually goes to zero after trapped pressure stabilizes.
• With static blocked in a climb, ASI reads lower than actual.
• With static blocked in a descent, ASI reads higher than actual.
• Position error happens when airflow around the aircraft causes the pitot or static source to sense incorrect pressure.
• Instrument error is caused by imperfections in the instrument mechanism.
• Density error explains why indicated airspeed and true airspeed differ as altitude and temperature change.
• Compressibility error becomes more important at higher speeds and higher altitudes.
• Altimeter setting error causes the altimeter to indicate an incorrect altitude.
• Temperature error affects true altitude; cold air makes the aircraft lower than the altimeter indicates.
• VSI lag means the VSI takes time to catch up to the actual rate of climb or descent.
• A static leak or alternate static source can cause altitude and airspeed errors.
• Always cross-check pitot-static instruments with attitude, power, GPS groundspeed, vertical trend, and expected aircraft performance.

3.3 Gyroscopic Systems and Instruments

Principles.

• Gyroscopic instruments use a rapidly spinning rotor to create a stable reference.
• The two key gyroscopic principles are rigidity in space and precession.
• Rigidity in space means a spinning gyro tends to keep its axis pointed in the same direction.
• Precession means an applied force is felt about 90 degrees later in the direction of rotation.
• Gyro instruments need a power source, usually vacuum, pressure, or electricity.
• The attitude indicator uses gyro rigidity to show pitch and bank.
• The heading indicator uses gyro rigidity to provide a stable directional reference.
• The turn coordinator and turn-and-slip indicator use gyro precession to show rate of turn.
• A free gyro is mounted in gimbals so it can remain stable while the aircraft moves around it.
• An attitude gyro is usually mounted with its spin axis vertical.
• A heading gyro is usually mounted with its spin axis horizontal.
• Gyros can drift because of friction, bearing errors, earth rotation, and transport across the earth.
• The heading indicator must be periodically aligned with the magnetic compass.
• The attitude indicator may have limits and can tumble if pitch or bank limits are exceeded in older systems.
• Vacuum-driven gyros can fail if suction is too low or too high.
• Electric gyros can fail with electrical power loss.
• Many aircraft use different power sources for different instruments to reduce common-mode failure.
• Modern glass systems may use AHRS instead of spinning mechanical gyros, but the displayed attitude/heading concepts remain similar.
• Gyro failure is recognized by indications that disagree with other instruments, aircraft attitude, or expected performance.

3.3 Gyroscopic Systems and Instruments - Power sources.

• Gyroscopic instruments need a power source to spin the gyro rotor.
• Common gyro power sources are vacuum, pressure, electric, and electronic AHRS systems.
• Vacuum systems use engine-driven suction to spin air-driven gyro instruments.
• Pressure systems use pressure air instead of suction to drive some gyro instruments.
• Electric gyros use electrical power to spin the gyro.
• Many traditional light aircraft use vacuum power for the attitude indicator and heading indicator.
• Many traditional light aircraft use electric power for the turn coordinator or turn-and-bank indicator.
• Using different power sources reduces the chance that one failure removes all gyro information.
• A vacuum failure commonly affects vacuum-driven attitude and heading instruments.
• An electrical failure can affect electric gyros, turn coordinator, avionics, and glass cockpit displays.
• A suction gauge or annunciator helps monitor vacuum-system health.
• Low suction may cause slow gyro spin, lazy indications, drift, or instrument failure.
• High suction can damage gyro bearings or create abnormal instrument operation.
• A gyro may continue to spin briefly after power loss, so failure may not be instant.
• Vacuum-driven attitude and heading indicators can slowly become unreliable after suction loss.
• The magnetic compass becomes an important backup if the heading indicator becomes unreliable.
• The turn coordinator can be a key backup for partial-panel flying if it is powered separately.
• Modern glass cockpits often use electrically powered AHRS instead of mechanical spinning gyros.
• AHRS requires electrical power and valid sensor inputs; it may display red Xs, flags, or comparator warnings if unreliable.
• Always identify which instruments share the same power source in the specific aircraft.

Errors.

• Gyroscopic instrument errors come from drift, precession, friction, power-source problems, gimbal limits, acceleration, turns, and instrument wear.
• Rigidity in space makes gyros useful, but it also means the aircraft and earth move around the gyro reference.
• Precession is the tendency of an applied force to show about 90 degrees later in the direction of gyro rotation.
• Real drift is caused by friction, bearing wear, imbalance, or other mechanical imperfections.
• Apparent drift is caused by earth rotation and aircraft movement over the earth.
• The heading indicator is not north-seeking and must be checked against the magnetic compass.
• The heading indicator can drift over time and should be realigned regularly in straight-and-level, unaccelerated flight.
• Attitude indicators may show small errors during acceleration, deceleration, turns, or skids.
• Older attitude indicators may tumble if pitch or bank limits are exceeded.
• A vacuum failure can make vacuum-driven attitude and heading indicators slowly become unreliable.
• Low suction can make gyros spin too slowly, causing lazy or incorrect indications.
• High suction can damage gyro bearings or create abnormal gyro operation.
• Electric failure can affect electric gyros, AHRS, turn coordinator, and glass cockpit displays.
• A gyro may not fail instantly after power loss; it may spin down gradually and become misleading.
• Turn coordinators show rate of turn and roll tendency, not exact bank angle.
• The inclinometer ball shows slip or skid and is not gyroscopic.
• A slipping or skidding turn can make gyro indications harder to interpret.
• Gyro errors should be caught by cross-checking attitude, heading, turn rate, compass, power, pitot-static instruments, and aircraft performance.
• If one gyro disagrees with the rest of the panel, suspect instrument or power-source failure before trusting it.
• Partial-panel flying depends on knowing which instruments share the failed power source.

3.4 Magnetic Compass

Principles.

• The magnetic compass is the basic magnetic heading reference in the aircraft.
• Use the magnetic compass to set and periodically check the heading indicator.
• Read the compass against the lubber line after the card has settled.
• The compass is most reliable in straight-and-level, unaccelerated flight.
• Avoid relying on the compass during turns, acceleration, deceleration, turbulence, or steep bank.
• The compass indicates magnetic heading, not true heading.
• Apply variation to convert true heading to magnetic heading.
• Apply deviation using the aircraft compass correction card to get compass heading.
• A common memory chain is true, variation, magnetic, deviation, compass.
• Compass corrections must use the aircraft’s own compass correction card.
• Electrical equipment, avionics, metal objects, and aircraft magnetism can affect the compass.
• The heading indicator is easier to fly by, but it can drift and must be checked against the compass.
• In partial-panel flying, the compass may become the main heading reference if the heading indicator fails.
• Compass turns should be made using a known turn rate and careful rollout correction.
• In the Northern Hemisphere, use UNOS for turning errors: undershoot north, overshoot south.
• When rolling out on a northerly heading, start rollout before the compass reaches the target heading.
• When rolling out on a southerly heading, start rollout after the compass passes the target heading.
• In the Northern Hemisphere, use ANDS for acceleration errors: accelerate north, decelerate south.
• On east or west headings, acceleration makes the compass indicate a turn toward north.
• On east or west headings, deceleration makes the compass indicate a turn toward south.
• Compass errors are greatest on north and south headings for turns, and on east and west headings for acceleration.
• Use smooth control inputs and let the compass stabilize before using it for accurate navigation.

3.4 Magnetic Compass - Use of the magnetic compass.

• The magnetic compass is the basic magnetic heading reference in the aircraft.
• Use the magnetic compass to set and periodically check the heading indicator.
• Read the compass against the lubber line after the card has settled.
• The compass is most reliable in straight-and-level, unaccelerated flight.
• Avoid relying on the compass during turns, acceleration, deceleration, turbulence, or steep bank.
• The compass indicates magnetic heading, not true heading.
• Apply variation to convert true heading to magnetic heading.
• Apply deviation using the aircraft compass correction card to get compass heading.
• A common memory chain is true, variation, magnetic, deviation, compass.
• Compass corrections must use the aircraft’s own compass correction card.
• Electrical equipment, avionics, metal objects, and aircraft magnetism can affect the compass.
• The heading indicator is easier to fly by, but it can drift and must be checked against the compass.
• In partial-panel flying, the compass may become the main heading reference if the heading indicator fails.
• Compass turns should be made using a known turn rate and careful rollout correction.
• In the Northern Hemisphere, use UNOS for turning errors: undershoot north, overshoot south.
• When rolling out on a northerly heading, start rollout before the compass reaches the target heading.
• When rolling out on a southerly heading, start rollout after the compass passes the target heading.
• In the Northern Hemisphere, use ANDS for acceleration errors: accelerate north, decelerate south.
• On east or west headings, acceleration makes the compass indicate a turn toward north.
• On east or west headings, deceleration makes the compass indicate a turn toward south.
• Compass errors are greatest on north and south headings for turns, and on east and west headings for acceleration.
• Use smooth control inputs and let the compass stabilize before using it for accurate navigation.

Errors.

• Magnetic compass errors come from variation, deviation, magnetic dip, turning, acceleration, deceleration, oscillation, and magnetic interference.
• The magnetic compass indicates magnetic direction, not true direction.
• Variation is the angle between true north and magnetic north.
• East variation is subtracted when converting true heading to magnetic heading.
• West variation is added when converting true heading to magnetic heading.
• Deviation is compass error caused by magnetic fields in the aircraft.
• Deviation is corrected using the aircraft compass correction card.
• Magnetic dip is caused by the vertical component of the earth’s magnetic field pulling the compass magnet downward.
• Magnetic dip causes turning errors and acceleration/deceleration errors.
• In the Northern Hemisphere, use UNOS for turning errors: undershoot north, overshoot south.
• When rolling out on a northerly heading, start rollout before the compass reaches the desired heading.
• When rolling out on a southerly heading, start rollout after the compass passes the desired heading.
• Turning errors are greatest on north and south headings.
• Turning errors are least on east and west headings.
• In the Northern Hemisphere, use ANDS for acceleration errors: accelerate north, decelerate south.
• On east or west headings, acceleration causes the compass to indicate a turn toward north.
• On east or west headings, deceleration causes the compass to indicate a turn toward south.
• Acceleration/deceleration errors are greatest on east and west headings.
• Acceleration/deceleration errors are least on north and south headings.
• Oscillation error is compass swinging caused by turbulence, rough control input, or aircraft movement.
• Magnetic interference can come from electrical equipment, avionics, metal objects, headsets, phones, or aircraft wiring.
• The compass is most reliable in straight-and-level, unaccelerated flight.
• Let the compass settle before using it for accurate heading checks.
• Do not chase the compass card during turns; use a controlled turn rate and rollout correction.

3.5 VOR

Serviceability checks.

• A VOR serviceability check confirms that the VOR receiver and selected facility are suitable for navigation.
• Before using a VOR, check NOTAMs for outages, maintenance, calibration, or unmonitored status.
• Tune the correct VOR frequency.
• Aurally identify the VOR using the Morse code identifier.
• Do not use a NAVAID if the identifier is missing when it should be present.
• Confirm the cockpit display gives the expected indications.
• Check that the CDI, TO/FROM flag, and navigation flag behave normally.
• A VOR with a navigation warning flag or unreliable identification must not be trusted.
• Dual VOR receivers may be checked by tuning both receivers to the same VOR facility.
• For a dual VOR check, compare the indicated bearings to the same station.
• If the two VOR receivers differ by more than 4 degrees, one receiver may be outside acceptable tolerance.
• If a dual VOR check is outside tolerance, investigate and correct the error before using the equipment for IFR flight.
• An airborne VOR check may be done by flying over a landmark located on a published radial.
• During an airborne VOR check, compare the indicated radial with the published radial.
• If airborne VOR equipment varies by more than plus or minus 6 degrees from the published radial, it should not be used for IFR navigation.
• Published VOR radials are flight-checked and have defined accuracy standards.
• Unpublished radials are not required to meet the same standard and may be affected by siting problems.
• Any significant published-radial anomalies associated with an aerodrome VOR may be published in the CFS.
• If abnormal VOR operation is suspected, report it to the appropriate ATS facility.
• A VOR check does not replace good navigation cross-checking.
• Cross-check VOR position with chart, heading, DME if available, GPS/RNAV if approved, and overall situational awareness.
• For INRAT purposes, remember the key tolerances: dual VOR 4 degrees, airborne check 6 degrees.

Interpretation and use.

• A VOR is a ground-based navigation aid that provides magnetic bearing information to or from the station.
• VOR radials are magnetic courses extending outward from the station.
• The 090 radial is east of the station, the 180 radial is south of the station, and so on.
• A radial is always named by the direction from the station, not toward the station.
• The OBS selects the course you want to reference.
• The CDI shows whether the selected course is left or right of the aircraft.
• The TO/FROM indicator shows whether the selected course takes you toward or away from the station.
• A FROM indication means the selected course is a radial outbound from the station.
• A TO indication means the selected course is the inbound course to the station.
• To fly inbound to a VOR on a specific radial, select the reciprocal course and confirm a TO indication.
• To fly outbound from a VOR on a specific radial, select that radial and confirm a FROM indication.
• To identify which radial you are on, centre the CDI with a FROM indication; the OBS value is the radial.
• To track a VOR course, turn toward the CDI needle when flying in the same direction as the selected course.
• If the CDI is left, the selected course is left of the aircraft.
• If the CDI is right, the selected course is right of the aircraft.
• Do not chase the needle; use an intercept angle, then correct for wind to maintain the course.
• Station passage is shown by CDI sensitivity, possible needle swing, and TO/FROM change.
• Near the station, the cone of confusion can make indications unstable or unreliable.
• VOR can be used for airway tracking, position fixes, holds, procedure turns, approaches, and cross-radial fixes.
• Two VOR radials from different stations can be used to determine a position fix.
• VOR/DME gives both radial information and distance from the station, if DME is available and serviceable.
• Always identify the VOR aurally before use.
• Check NOTAMs, flags, receiver serviceability, and charted information before relying on a VOR.
• VOR is line-of-sight, so reception can be limited by altitude, distance, terrain, and aircraft position.
• Published VOR radials have defined accuracy standards; unpublished radials should not be treated the same way.

Limitations.

• VOR is a short-distance, line-of-sight navigation aid.
• VOR range depends on altitude, terrain, station power, aircraft position, and shadowing.
• Higher altitude generally improves VOR reception range.
• Low altitude, terrain, buildings, and distance can reduce or block VOR reception.
• VOR signals can be unreliable below radio line-of-sight or behind terrain.
• Near station passage, the cone of confusion can cause rapid CDI movement, TO/FROM changes, or unreliable indications.
• VOR gives azimuth guidance only; it does not give distance unless DME is available.
• A VOR radial alone tells you a line of position, not an exact aircraft position.
• A fix normally requires another radial, DME, GPS/RNAV, crossing bearing, or other position information.
• Published VOR radials have accuracy standards; unpublished radials may not meet the same standard.
• Do not assume an unpublished radial is suitable for IFR navigation or procedure use.
• VOR indications must not be used unless the facility has been identified aurally.
• A missing Morse identifier can mean the NAVAID is unreliable or unavailable.
• A navigation flag, OFF flag, or abnormal indication means the VOR should not be trusted.
• NOTAMs may remove a VOR from service or identify it as unmonitored.
• An unmonitored VOR may still be usable, but the pilot must monitor it carefully for proper operation.
• Portable electronic devices and aircraft electrical interference can affect navigation equipment.
• Receiver accuracy must be checked; dual VORs should agree within 4 degrees.
• Airborne VOR checks must be within plus or minus 6 degrees of the published radial for IFR navigation.
• VOR is being supplemented or replaced in many operations by RNAV/GNSS, but it remains important for conventional IFR navigation.
• VOR does not provide vertical guidance.
• A centred CDI does not guarantee terrain clearance, obstacle clearance, procedure compliance, or ATC clearance.
• VOR tracking requires wind correction; a centred needle can drift off again if wind is not corrected.
• VOR sensitivity increases closer to the station because each degree of radial spacing represents less distance.
• Always cross-check VOR information with chart position, heading, timing, DME if available, GPS/RNAV if approved, and situational awareness.

3.6 ADF

Serviceability checks.

• ADF serviceability checks confirm that the aircraft ADF receiver and the selected NDB are usable for navigation.
• Before using an ADF/NDB, check NOTAMs for outages, maintenance, unserviceability, or unmonitored status.
• Tune the correct NDB frequency.
• Aurally identify the NDB using the Morse code identifier before relying on it.
• Do not use the NDB if the identifier is missing, wrong, irregular, or not positively confirmed.
• Confirm the ADF needle gives a sensible bearing indication.
• The ADF needle should point toward the station when operating normally in ADF mode.
• Check that the ADF is in the correct operating mode, not left in ANT mode if bearing information is required.
• ANT mode may improve audio reception but normally does not provide normal bearing information.
• Use BFO mode if required to identify certain unmodulated beacons, according to aircraft equipment procedures.
• If the ADF has a test function, use it according to the POH/AFM or avionics manual.
• Compare the ADF indication with known aircraft position, charted station location, heading, and other navigation sources.
• A grossly unreasonable bearing means the ADF or NDB should not be trusted.
• ADF indications can be affected by electrical interference from aircraft equipment or portable electronic devices.
• Handheld electronic calculators and other devices may interfere with airborne ADF equipment if close to the antenna or lead-in wiring.
• ADF/NDB signals can be affected by night effect, terrain, shoreline refraction, thunderstorms, and other propagation disturbances.
• ADF does not normally provide the same positive failure flag logic as modern VOR/GNSS systems, so pilot monitoring is important.
• If abnormal ADF/NDB operation is suspected, report it to the appropriate ATS facility when practical.
• A serviceability check does not make the ADF precise; it only confirms the equipment appears usable.
• For IFR use, cross-check ADF position information with chart, heading, timing, VOR, DME, GNSS/RNAV if approved, and situational awareness.

Interpretation and use.

• ADF is the aircraft receiver/display used to navigate using an NDB signal.
• The ADF needle points toward the NDB station.
• ADF gives bearing to the station, not distance.
• The basic ADF display shows relative bearing: the angle between the aircraft nose and the station.
• Relative bearing is measured clockwise from the aircraft nose to the ADF needle.
• Magnetic bearing to the station equals magnetic heading plus relative bearing.
• If the result is greater than 360 degrees, subtract 360 degrees.
• Bearing from the station is the reciprocal of bearing to the station.
• A fixed-card ADF has 0 degrees at the top and requires mental calculation with aircraft heading.
• A movable-card ADF can be manually set to aircraft heading to show magnetic bearing more directly.
• An RMI automatically rotates with aircraft heading and points to the station using a bearing pointer.
• To home to an NDB, turn the aircraft until the ADF needle points straight ahead.
• Homing is simple but allows wind to curve the flight path downwind.
• To track to an NDB, use wind correction to maintain a desired inbound bearing.
• To track from an NDB, use the bearing from the station and correct for wind.
• ADF can be used for station passage, position fixes, holding, NDB approaches, and general orientation.
• Station passage is indicated when the needle swings rapidly through 90 degrees and then points behind the aircraft.
• A single ADF bearing gives a line of position, not an exact position.
• A fix requires another bearing, crossing radial, DME, GNSS/RNAV, or other position information.
• Always identify the NDB aurally before using it.
• ADF is useful as a backup navigation source but is less precise than VOR or GNSS.
• ADF indications must be cross-checked because NDB signals are vulnerable to night effect, terrain, coastlines, thunderstorms, and electrical interference.

3.6 ADF - Limitations.

• ADF/NDB is a bearing-only navigation system.
• ADF does not provide distance to the station.
• A single ADF bearing gives a line of position, not an exact fix.
• ADF/NDB is generally less precise than VOR, DME, or GNSS.
• ADF indications can be affected by night effect, especially around sunrise and sunset.
• Night effect can make the needle wander or point inaccurately because radio waves reflect from the ionosphere.
• Thunderstorms can cause large ADF errors because lightning and static discharge can attract or disturb the needle.
• Terrain effect can bend or reflect NDB signals, especially near mountains or high ground.
• Shoreline effect can occur when the signal crosses a coastline at a shallow angle.
• ADF/NDB signals can be affected by electrical interference from aircraft systems or portable electronic devices.
• ADF may point toward strong electrical interference instead of the NDB.
• ADF signals can be weaker or less reliable at long range.
• Station interference can occur when two NDBs or radio stations on similar frequencies affect the receiver.
• ADF accuracy depends on correct tuning, correct identification, receiver condition, and signal quality.
• The ADF needle may fluctuate or lag during turns, turbulence, or poor reception.
• ADF homing in wind creates a curved ground track unless wind correction is applied.
• ADF does not provide vertical guidance.
• ADF does not guarantee obstacle clearance, procedure compliance, or ATC clearance.
• Some ADF systems may give misleading indications without an obvious warning flag.
• Always aurally identify the NDB before use and cross-check with other navigation sources when available.

3.7 ILS

Basic components: air and ground.

• ILS stands for Instrument Landing System.
• ILS provides precision final approach guidance to a runway.
• ILS gives both horizontal guidance and vertical guidance.
• Horizontal guidance comes from the localizer.
• Vertical guidance comes from the glide path or glide slope.
• The localizer guides the aircraft to the runway centreline.
• The glide path guides the aircraft on the correct descent path.
• A typical ILS glide path is about 3 degrees.
• The localizer transmitter antenna is normally located beyond the far end of the runway.
• The glide path antenna is normally near the approach end of the runway and offset from the runway centreline.
• The aircraft ILS receiver receives the localizer and glide path signals.
• The cockpit display may show ILS guidance on a CDI, HSI, attitude indicator, flight director, or electronic flight display.
• The localizer needle shows left-right displacement from the runway centreline course.
• The glide path needle shows above-below displacement from the desired descent path.
• ILS guidance must be identified before use by checking the correct frequency and identifier.
• The ILS identifier is normally transmitted on the localizer frequency.
• Many ILS procedures use a FAF identified by an NDB, DME fix, or RNAV fix.
• DME, if paired with the ILS, may provide distance information for fixes such as the IAF or MAP.
• Approach lighting is not part of the radio guidance itself, but it is important for lower-minima ILS operations.
• CAT II and CAT III ILS operations require extra serviceable ground equipment, aircraft equipment, procedures, and approvals.
• ILS is more precise than a localizer-only approach because it provides vertical guidance as well as lateral guidance.
• If the glide path is not available or not authorized, the approach may become localizer-only and uses non-precision minima.
• A full ILS requires both localizer and glide path guidance to be usable.
• A back course localizer is not a normal ILS and does not provide a usable glide path.

Principles of operation.

• ILS provides precision approach guidance using lateral guidance from the localizer and vertical guidance from the glide path.
• The localizer guides the aircraft left or right toward the runway centreline.
• The glide path guides the aircraft above or below the desired descent path.
• The cockpit display normally shows two needles: one for localizer and one for glide path.
• Localizer needle displacement means the selected final approach course is to the left or right of the aircraft.
• Glide path needle displacement means the aircraft is above or below the desired glide path.
• The pilot normally flies toward the needles to recapture the centreline and glide path.
• A centred localizer needle means the aircraft is laterally aligned with the localizer course.
• A centred glide path needle means the aircraft is on the vertical descent path.
• The localizer signal is normally much more sensitive than a VOR course.
• Localizer sensitivity increases close to the runway because it is angular guidance.
• Small needle movements near the runway can represent small angular errors but important runway-alignment errors.
• The glide path is also angular guidance, so precise pitch and power control are needed.
• A typical ILS glide path is approximately 3 degrees.
• The localizer frequency is selected in the aircraft; the associated glide path frequency is paired automatically.
• ILS identification is transmitted on the localizer frequency and must be checked before use.
• The localizer antenna is normally beyond the far end of the runway.
• The glide path antenna is normally near the approach end and offset from the runway centreline.
• DME, NDB, or RNAV fixes may be used to identify approach fixes such as the FAF, depending on the published procedure.
• DME distance, when used, is slant range, not exact horizontal distance.
• ILS guidance does not remove the need to follow the published approach, altitude restrictions, minima, missed approach instructions, and ATC clearance.
• If the glide path is not available or not authorized, the approach may become localizer-only and must use non-precision minima.
• A back course localizer normally provides lateral guidance only and no usable glide path.
• If an ILS flag appears, identifier is wrong or missing, or the indications are unreasonable, do not rely on the ILS.

3.7 ILS - Limitations.

• ILS is precise, but it is not immune to signal, equipment, procedure, or pilot-use limitations.
• ILS provides guidance only when the correct facility is tuned, identified, serviceable, and properly displayed.
• A missing, incorrect, or unreliable identifier means the ILS should not be trusted.
• Localizer guidance is angular, so sensitivity increases as the aircraft gets closer to the runway.
• Small localizer deviations near the runway can represent important alignment errors.
• Glide path guidance is also angular and requires precise pitch and power control.
• ILS guidance does not replace ATC clearance, approach clearance, published altitudes, minima, required visual reference, or missed approach procedures.
• A centred localizer and glide path only show electronic alignment; they do not by themselves authorize descent or landing.
• False localizer courses or false captures may occur, especially if approach mode is armed too early or too far from the correct course.
• A coupled approach should not be initiated until the aircraft is within 6 degrees of the localizer centreline.
• Approach mode should normally not be selected until the aircraft is within 18 NM of the threshold and within 6 degrees of the inbound ILS course.
• Confirm localizer capture with raw data, heading, charted track, and another navigation source such as ADF, RNAV, or DME when available.
• Course interference is normally negligible within 6 degrees of the localizer centreline, but anomalies can exist and may be charted.
• Electromagnetic interference can affect localizer receivers and may cause erratic, erroneous, or even apparently normal indications.
• If the localizer goes off the air, the warning flag may not always give an obvious warning in every situation.
• Glide path signals can be affected by conditions near the glide path antenna, including heavy snow buildup in the beam-forming area.
• At runways with ILS at both ends, the systems are interlocked so only one ILS operates at a time.
• ILS critical areas must be protected for reliable low-visibility and autoland operations.
• Vehicles, aircraft, or surface traffic in ILS critical areas can disturb the localizer or glide path signal.
• CAT II and CAT III operations require fully serviceable ground systems, lighting, RVR equipment, power, approved aircraft equipment, procedures, and authorization.
• CAT I equipment or signal quality does not automatically support autoland or lower-category operations.
• If the glide path is unavailable or not authorized, the approach becomes localizer-only if published and must use non-precision minima.
• A back course localizer normally provides lateral guidance only and no usable glide path.
• ILS has no protection against poor aircraft handling; unstable approach criteria still apply.
• Any abnormal ILS indication should be treated seriously and reported to ATS when appropriate.

3.7 ILS - Localizer only.

• A localizer-only approach uses the ILS localizer for lateral guidance only.
• Localizer-only does not provide usable vertical glide path guidance.
• Because there is no glide path, a localizer-only approach is a non-precision approach.
• Localizer-only approaches use an MDA, not a DA.
• The pilot descends to the published MDA and maintains it until the missed approach point or until visual landing requirements are met.
• If the glide path is unavailable during an ILS, the approach may be flown as localizer-only only if localizer-only minima are published and the approach is authorized.
• Do not use ILS decision altitude when flying localizer-only.
• The localizer provides runway-centreline course guidance.
• The localizer is more sensitive than a VOR radial.
• Localizer sensitivity increases as the aircraft gets closer to the runway.
• Small localizer deviations near the runway can represent important alignment errors.
• A localizer-only approach may have step-down fixes and altitude restrictions.
• Respect all published crossing altitudes, step-down fixes, timing, DME distances, or RNAV fixes.
• The missed approach point may be identified by timing, DME, RNAV fix, or another charted method.
• Localizer-only final descent may be flown using a stabilized constant descent technique, but the MDA remains the hard minimum altitude.
• A centred localizer needle means lateral alignment only; it does not confirm vertical path, obstacle clearance outside procedure limits, or landing clearance.
• The localizer frequency must be tuned and identified before use.
• The ILS/localizer identifier is normally transmitted on the localizer frequency.
• A LOC flag, wrong identifier, missing identifier, or unreasonable indication means the localizer should not be trusted.
• A back course localizer is also lateral guidance only and normally has no usable glide path.
• Use the published LOC minima, not ILS minima, whenever vertical guidance is not being used.

3.8 GNSS

3.8 GNSS - GPS basic principles: air and ground.

• GNSS means Global Navigation Satellite System.
• GPS is the United States satellite constellation within GNSS.
• GNSS provides worldwide position, navigation, and time information.
• The basic GNSS system includes space, ground, and aircraft components.
• The space component is the satellite constellation.
• The GPS constellation uses satellites orbiting the earth and broadcasting navigation signals.
• The ground component monitors and controls the satellite constellation.
• Ground control stations track satellites, update satellite data, and command satellites when needed.
• The aircraft component is the GNSS receiver, antenna, cockpit display, and approved installation.
• The aircraft receiver measures signal travel time from satellites.
• Because radio signals travel at approximately the speed of light, travel time can be converted into distance.
• This calculated satellite distance is called pseudorange.
• The receiver uses pseudoranges from multiple satellites to calculate aircraft position.
• A GPS receiver normally needs four satellites to calculate a 3D position and correct receiver clock error.
• Satellite ephemeris data tells the receiver where each satellite is in orbit.
• Accurate GPS depends on satellite clocks, satellite orbit data, signal propagation, and satellite geometry.
• Satellite geometry matters: widely spread satellites give better accuracy than satellites clustered together.
• The receiver can also calculate groundspeed and track from position changes over time.
• GNSS does not need a ground-based NAVAID on the route, but it still needs satellite signal reception and integrity.
• Integrity means the system can warn the pilot if position information should not be trusted.
• RAIM is an aircraft-based integrity check used by many IFR GPS receivers.
• RAIM uses extra satellites to compare position solutions and detect possible errors.
• SBAS, such as WAAS, uses ground reference stations and geostationary satellites to improve accuracy and integrity.
• IFR GNSS equipment must be approved and installed for IFR use.
• Handheld or VFR-only GPS units are not approved for IFR navigation because they do not meet IFR certification and integrity requirements.
• For IFR use, the pilot must understand receiver modes, database use, integrity alerts, CDI sensitivity, and the approved operating procedures.

3.8 GNSS - Limitations.

• GNSS is highly accurate, but it is not unlimited or failure-proof.
• GNSS depends on satellite signal reception, satellite geometry, receiver integrity monitoring, current databases, approved equipment, and correct pilot use.
• GPS signals are weak and can be affected by antenna blockage, terrain masking, aircraft structure, interference, jamming, or spoofing.
• Satellite geometry affects accuracy; widely spread satellites give better geometry than clustered satellites.
• Ionospheric delay, atmospheric effects, satellite clock error, and orbit error can affect position accuracy.
• RAIM availability depends on the number of visible satellites and their geometry.
• A basic GPS position normally needs four satellites, but RAIM requires extra satellites to monitor integrity.
• RAIM generally requires at least five satellites to detect a problem.
• FDE generally requires at least six satellites with suitable geometry to detect and exclude a faulty satellite.
• If a RAIM alert occurs, GNSS integrity is not assured.
• Except in an emergency, GNSS must not be used for IFR navigation after an applicable integrity alert.
• If GNSS becomes unavailable en route, use conventional navigation aids, advise ATS, and obtain a new clearance if required.
• GNSS is not a substitute for required aircraft equipment, procedure approval, database currency, or pilot knowledge.
• Handheld or VFR-only GPS units cannot be used as IFR navigation equipment.
• IFR GNSS equipment must be certified, installed, approved, and used according to its operating limitations.
• GNSS approach procedures must be loaded from a current approved avionics database.
• Pilot-created waypoints must not be used to build instrument approach procedures.
• Database errors, wrong waypoint selection, or incorrect procedure loading can create serious navigation errors.
• CDI sensitivity changes by phase of flight; en route, terminal, and approach sensitivity are not the same.
• The pilot must verify the correct mode, approach type, waypoint sequence, and active leg.
• LNAV provides lateral guidance only and uses MDA.
• LNAV/VNAV and LPV provide vertical guidance and use DA, but only if the aircraft and procedure are authorized.
• Advisory vertical guidance on an LNAV approach does not change the published MDA or step-down restrictions.
• Baro-VNAV can be affected by altimeter setting errors and temperature.
• WAAS/SBAS improves accuracy and integrity but does not remove the need to follow procedure limits and equipment requirements.
• GNSS distance is normally distance to the active waypoint, not necessarily distance to the runway, station, or fix ATC asks about.
• GNSS can reduce dependence on ground NAVAID reception, but pilots must still consider communication coverage, controlled airspace, terrain, and alternate navigation.

3.8 GNSS - Equipment.

• GNSS equipment for IFR must be approved, installed, and operated according to its limitations.
• GNSS capability may come from a panel-mounted GPS/GNSS receiver or from an FMS using an approved GNSS sensor.
• The aircraft needs a suitable GNSS antenna, receiver, cockpit display, navigation database, and approved aircraft installation.
• Handheld GPS and VFR-only GPS units cannot be used as IFR navigation equipment.
• IFR GNSS equipment must provide required accuracy, integrity, availability, and continuity for the intended operation.
• Integrity monitoring warns the pilot when the GNSS position should not be trusted for the current phase of flight.
• RAIM is aircraft-based augmentation used by many IFR GPS receivers.
• RAIM uses extra satellites to detect possible position errors.
• FDE can detect and exclude a faulty satellite if the equipment and satellite geometry support it.
• WAAS is satellite-based augmentation that improves accuracy and integrity.
• WAAS-capable receivers can support vertically guided RNAV approaches such as LPV, if the aircraft and procedure are authorized.
• Older TSO-C129/C129a GPS equipment may support en route, terminal, and non-precision approach operations, but RAIM prediction and equipment limitations matter.
• TSO-C145/C146 WAAS equipment supports improved GNSS capability and may allow LPV or LNAV/VNAV operations where published.
• The avionics database must be current for IFR approach use.
• Instrument approaches must be loaded from the approved database, not manually built using pilot-created waypoints.
• The pilot must verify the correct approach, runway, transition, waypoint sequence, active leg, CDI sensitivity, and annunciated mode.
• GNSS equipment changes sensitivity by phase of flight, such as en route, terminal, and approach.
• Most avionics automatically change to terminal sensitivity near the destination or when an arrival is loaded.
• For approach operations, the receiver must show the correct approach mode and required integrity before the final approach segment.
• If a RAIM or integrity alert occurs, the pilot must not continue using GNSS for IFR navigation except in an emergency.
• Advisory vertical guidance on an LNAV approach does not make the equipment approved for LPV or LNAV/VNAV minima.
• Aircraft using baro-VNAV need approved barometric vertical navigation equipment and correct altimeter/temperature considerations.
• The pilot must know how to retrieve distances to waypoints, including waypoints that are not the active waypoint if ATC asks.
• GNSS equipment is powerful, but pilot setup errors can be as dangerous as equipment failures.

3.8 GNSS - Interpretation.

• GNSS interpretation means understanding what the receiver is guiding you to, what mode it is in, and whether the guidance is valid for the phase of flight.
• Always confirm the correct flight plan, procedure, runway, transition, and active leg.
• The active waypoint is the waypoint the receiver is currently navigating toward.
• Distance shown is normally distance to the active waypoint, not automatically distance to the runway or airport.
• Desired track is the planned ground track from the previous waypoint to the active waypoint.
• Track is the aircraft's actual path over the ground.
• Bearing is the direction from the aircraft to the selected waypoint.
• Heading is where the aircraft nose points; track is where the aircraft is actually moving over the ground.
• Cross-track error shows how far the aircraft is left or right of the desired course.
• The CDI or course deviation display shows left-right displacement from the selected GNSS course.
• Fly toward the CDI needle to reduce lateral course error.
• GNSS course guidance is based on track over the ground, not just aircraft heading.
• Groundspeed, ETE, and ETA are calculated from GPS position change over time.
• GNSS sequencing automatically changes from one waypoint to the next when the aircraft crosses sequencing criteria.
• Suspended sequencing means the receiver will not automatically advance to the next waypoint until the pilot takes action.
• On approaches, check the annunciated mode such as LNAV, LNAV/VNAV, LPV, or advisory vertical guidance.
• LNAV gives lateral guidance only and uses MDA.
• LNAV/VNAV and LPV give approved vertical guidance when the equipment and procedure support it, and use DA.
• Advisory vertical guidance on an LNAV approach does not change LNAV minima, step-down altitudes, or the MDA.
• CDI sensitivity changes with phase of flight, such as en route, terminal, and approach.
• Terminal sensitivity is required for GNSS terminal operations.
• Approach sensitivity must be active before relying on final approach guidance.
• Integrity messages and RAIM alerts must be interpreted immediately; if integrity is lost, GNSS guidance cannot be trusted for IFR except in emergency.
• GNSS approaches must be loaded from the current approved database, not manually built from pilot-created waypoints.
• A magenta line is not clearance, terrain protection, or permission to descend.
• Always compare GNSS interpretation with the chart, clearance, altitude restrictions, navigation mode, and aircraft position.

3.8 GNSS - RAIM, Fault Detection and Exclusion.

• RAIM stands for Receiver Autonomous Integrity Monitoring.
• RAIM is an aircraft-based integrity monitoring function used by many IFR GNSS receivers.
• RAIM checks whether the GNSS position solution can be trusted for the current phase of flight.
• RAIM uses extra satellites in view to compare position solutions and detect possible errors.
• A basic GPS navigation solution normally requires four satellites.
• RAIM normally requires at least five satellites with suitable geometry.
• RAIM availability depends on the number of visible satellites and their geometry.
• Poor satellite geometry can make RAIM unavailable even if enough satellites appear to be in view.
• RAIM can support en route, terminal, and non-precision approach phases when available.
• RAIM alert limits vary by phase of flight.
• Typical alert limits are 2 NM en route, 1 NM terminal, and 0.3 NM for non-precision approach operations.
• If RAIM cannot guarantee integrity, the receiver alerts the pilot.
• A RAIM availability alert does not necessarily mean a satellite has failed; it can mean the geometry is not good enough.
• Except in an emergency, pilots must discontinue using GNSS for IFR navigation when the applicable integrity alert occurs.
• A second type of RAIM alert can occur when the receiver detects a satellite range error that may degrade accuracy beyond the alert limit.
• When a serious satellite range error is detected, the receiver may deny navigation guidance and show warning flags.
• FDE stands for Fault Detection and Exclusion.
• FDE can detect which satellite is faulty and exclude it from the navigation solution.
• FDE normally requires at least six satellites with good geometry.
• FDE improves continuity because navigation may continue after a faulty satellite is excluded.
• RAIM detects a problem; FDE may detect and remove the bad satellite.
• RAIM prediction may be required before flight or before commencing certain GNSS approaches, especially with older TSO-C129/C129a equipment.
• If approach-level RAIM is not expected, the pilot should plan another approach, delay, or proceed to an alternate as appropriate.
• WAAS/SBAS-capable receivers may improve integrity availability, but the pilot must still respect alerts, modes, and equipment limitations.
• RAIM and FDE do not replace the need for an approved receiver, approved installation, current database, and correct pilot procedure.

3.8 GNSS - WAAS.

• WAAS stands for Wide Area Augmentation System.
• WAAS is a satellite-based augmentation system, or SBAS.
• WAAS improves GPS accuracy, integrity, and availability for aviation use.
• WAAS uses a network of ground reference stations to monitor GPS satellite signals.
• WAAS master stations process the reference-station data and calculate correction and integrity messages.
• WAAS messages are broadcast to aircraft through geostationary satellites.
• WAAS geostationary satellites can also act as additional ranging sources for navigation.
• WAAS corrections help reduce errors from satellite clocks, satellite orbit data, and ionospheric delay.
• WAAS integrity messages help validate satellite signal reliability.
• WAAS can provide the integrity required without relying on traditional RAIM in the same way older GPS receivers do.
• A WAAS-capable IFR receiver may support RNAV approaches with vertical guidance.
• WAAS enables LPV approaches where LPV minima are published.
• LPV provides lateral and vertical guidance that feels similar to ILS, but it is still an RNAV GNSS approach.
• WAAS may also support LNAV/VNAV minima depending on equipment, procedure, and authorization.
• WAAS does not turn every RNAV approach into an LPV approach.
• The approach chart must publish the minima to be used, such as LNAV, LNAV/VNAV, LP, or LPV.
• The receiver must annunciate the correct approach mode before the pilot uses that set of minima.
• LPV uses DA, not MDA, because it provides approved vertical guidance.
• LNAV uses MDA because it provides lateral guidance only.
• Advisory vertical guidance on an LNAV approach is not the same as WAAS-approved LPV or LNAV/VNAV guidance.
• WAAS requires suitable approved avionics, approved installation, current database, and correct pilot operation.
• WAAS improves capability, but the pilot must still obey approach clearance, altitude restrictions, minima, missed approach procedures, and required visual references.
• If the receiver gives an integrity alert or does not annunciate the expected approach mode, the pilot must not use the intended WAAS minima.
• WAAS is augmentation, not autopilot, not ATC clearance, and not a guarantee that the airplane is stable or legal to land.

3.9 Transponder

3.9 Transponder - Principles of operation.

• A transponder is an aircraft radio device that replies to ATS surveillance interrogations.
• The transponder helps ATC identify, track, and separate aircraft.
• Primary radar detects reflected energy from the aircraft, but secondary surveillance depends on the aircraft transponder replying.
• The ground surveillance system interrogates the aircraft transponder.
• The aircraft transponder replies with coded information.
• Mode A transmits the selected four-digit squawk code.
• The squawk code helps ATC identify the aircraft on the surveillance display.
• Mode C transmits automatic pressure-altitude information.
• Mode C altitude reporting helps ATC assess vertical separation and potential conflicts.
• Mode S performs Mode A and Mode C functions and also has data-link capability.
• Mode S uses a unique aircraft address, allowing selective interrogation and improved surveillance functions.
• ADS-B Out, where installed, uses aircraft position and identity data to support surveillance, but it is not the same thing as basic Mode A/C transponder operation.
• IDENT is a feature that makes the aircraft target stand out on the ATC display when requested by ATS.
• Use IDENT only when requested by ATS.
• The pilot normally selects the assigned squawk code before switching the transponder out of standby.
• When no ATC code has been issued for IFR low-level operations, Code 1000 is commonly used unless instructed otherwise.
• IFR aircraft in high-level airspace normally use Mode A Code 2000 and Mode C unless otherwise instructed.
• VFR aircraft normally use Mode A Code 1200 at or below 12,500 ft ASL, unless assigned another code.
• Emergency codes are special Mode A codes: 7500, 7600, and 7700.
• Avoid accidentally selecting 7500, 7600, or 7700 while changing codes.
• Do not switch to STANDBY just to change codes, because ATC may lose the surveillance target.
• Mode C reports pressure altitude, not necessarily the same number shown on the altimeter set to local altimeter setting.
• ATC may ask the pilot to report altitude to validate the Mode C readout.
• A valid altitude readout is close enough to the pilot-reported altitude; a large difference may make the altitude readout invalid.
• If the transponder or Mode C fails in mandatory transponder airspace, ATC authorization or specific procedures may be required.

3.9 Transponder - Phraseology and use.

• Transponder phraseology tells the pilot what code, mode, or feature ATC wants used.
• SQUAWK followed by a code means select that assigned Mode A code.
• SQUAWK IDENT means press the IDENT feature so the aircraft target stands out on the ATC display.
• Use IDENT only when requested by ATS.
• SQUAWK MODE CHARLIE means activate Mode C automatic altitude reporting.
• STOP SQUAWK MODE CHARLIE means turn off automatic altitude reporting but continue transponder operation as directed.
• RESET TRANSPONDER means reset the transponder and transmit the currently assigned code again.
• REPORT YOUR ALTITUDE is used when ATC needs to compare the pilot-reported altitude with the Mode C readout.
• SQUAWK STANDBY means stop normal transponder replies until instructed to resume.
• When instructed by ATC about transponder operation, comply until further instruction, landing, emergency, communication failure, or unlawful interference.
• Select the assigned code before switching the transponder out of STANDBY.
• Do not select STANDBY just to change codes because ATC may lose the target.
• Avoid accidentally passing through emergency codes 7500, 7600, or 7700 while changing squawk codes.
• Use 7500 for unlawful interference, 7600 for communication failure, and 7700 for emergency.
• IFR aircraft in controlled low-level airspace normally use Mode A Code 1000 and Mode C if available, unless ATC instructs otherwise.
• IFR aircraft in high-level airspace normally use Mode A Code 2000 and Mode C unless ATC instructs otherwise.
• VFR aircraft normally use Code 1200 at or below 12,500 ft ASL unless assigned otherwise.
• VFR aircraft normally use Code 1400 above 12,500 ft ASL unless assigned otherwise.
• If an IFR flight plan is cancelled or changed to VFR, set the appropriate VFR code unless ATC instructs otherwise.
• If Mode C altitude reporting appears incorrect, ATC may validate it by comparing it with the altitude reported by the pilot.
• Transponder altitude readouts are displayed to ATC in 100-foot increments.
• At airports with MLAT surface surveillance procedures, transponders may need to remain transmitting on the manoeuvring area if published in the CAP or CFS.

3.10 Other Systems - Basic Principles and Use

DME.

• DME stands for Distance Measuring Equipment.
• DME provides distance from the aircraft to a ground DME station.
• DME distance is displayed in nautical miles.
• DME works by two-way signal exchange between the aircraft and the ground station.
• The aircraft sends paired pulse signals to the DME ground station.
• The ground station receives the aircraft signal and sends a reply on a different frequency.
• The aircraft measures the time required for the signal exchange.
• The DME unit converts elapsed time into distance.
• DME distance is slant range, not horizontal ground distance.
• Slant range is the straight-line distance from aircraft to station.
• Slant-range error is greatest when the aircraft is high and close to the station.
• DME is most accurate for practical navigation when the aircraft is farther from the station than its altitude error would matter.
• DME may be collocated with VOR, LOC, ILS, TACAN, or sometimes NDB facilities.
• VOR/DME gives both radial and distance information.
• ILS/DME or LOC/DME can provide distance information for approach fixes.
• DME may define fixes such as the IAF, FAF, step-down fixes, MAP, or holding distances.
• Many aircraft automatically select the paired DME channel when the VOR or LOC frequency is tuned.
• Some standalone DME equipment may require selecting the correct paired channel manually.
• DME operates in the UHF band and is limited by line-of-sight reception.
• DME range is similar to VOR range and depends on altitude, terrain, and signal coverage.
• DME does not provide bearing or course by itself.
• DME plus a VOR radial can give an exact fix from a VOR/DME station.
• DME should be identified and cross-checked with the charted facility and frequency pairing before use.
• Do not use apparent radial information from a DME-only or TACAN-derived distance source unless the aircraft is actually receiving valid VOR azimuth guidance.
• DME is useful for position awareness, timing replacement, descent planning, approach fixes, holds, and missed approach points.

VORTAC.

• VORTAC is a combined VOR and TACAN navigation facility.
• VOR provides civil aircraft with azimuth information in the form of radials.
• TACAN provides military aircraft with azimuth and DME-style slant-range distance.
• A VORTAC combines the VOR and TACAN components at one site.
• Civil aircraft normally use the VOR component for radial guidance.
• Civil aircraft equipped with DME can receive distance information from the TACAN DME component.
• When a pilot tunes the paired VOR frequency, suitable DME equipment can obtain distance from the TACAN portion of the VORTAC.
• The VOR portion gives bearing/radial information; the DME/TACAN portion gives distance.
• VORTAC distance is slant range, not exact horizontal ground distance.
• A VOR radial plus DME distance from a VORTAC gives a fix.
• VORTACs are useful for en route navigation, airways, position fixes, holding, approaches, and distance-based procedure steps.
• The pilot must tune the correct frequency or paired channel.
• The pilot must identify the facility before using it for navigation.
• VORTAC use is still subject to normal VOR and DME limitations, including line-of-sight reception.
• VOR reception can be affected by altitude, terrain, distance, and shadowing.
• DME reception is also line-of-sight and may be limited by terrain or low altitude.
• DME accuracy is still subject to normal DME tolerance and slant-range effects.
• VORTAC does not provide glidepath or vertical guidance.
• VORTAC guidance does not replace ATC clearance, published procedures, altitude restrictions, or obstacle clearance requirements.
• If only DME information is being received, any apparent radial information from incompatible equipment must be ignored.
• For IFR, cross-check VORTAC information with charts, identifiers, NOTAMs, cockpit flags, DME readout, and other navigation sources when available.

3.10 Other Systems - Basic Principles and Use - Area navigation (RNAV).

• RNAV stands for Area Navigation.
• RNAV allows an aircraft to navigate on a desired flight path instead of only flying directly to or from ground-based stations.
• RNAV can use ground-based NAVAIDs, self-contained systems, satellite navigation, or a combination of sources.
• RNAV-capable systems include GNSS, VOR/DME, DME/DME, INS, and IRS.
• RNAV navigation is normally based on waypoints, tracks, distances, and database-defined routes or procedures.
• A waypoint is a defined geographic position used for navigation.
• RNAV can create routes between waypoints that do not have to pass over a VOR, NDB, or other ground station.
• RNAV allows more flexible routing than conventional station-to-station navigation.
• RNAV can support en route navigation, terminal arrivals, departures, holds, approaches, and missed approaches.
• The aircraft equipment calculates position and gives guidance to the next active waypoint or leg.
• The active leg is the route segment the RNAV system is currently navigating.
• The pilot must verify the correct route, waypoint sequence, active leg, altitude restrictions, and navigation mode.
• RNAV guidance may be displayed on a CDI, HSI, flight director, moving map, or electronic flight display.
• RNAV lateral guidance is based on desired track and cross-track error.
• RNAV distance is usually distance to the active waypoint, not necessarily distance to the airport, runway, or nearest NAVAID.
• RNAV systems may automatically sequence from one waypoint to the next.
• Suspended sequencing means automatic waypoint advance is paused and may require pilot action.
• RNAV performance depends on the navigation source, equipment approval, database currency, integrity monitoring, and correct pilot operation.
• For RNAV procedures, the procedure must be loaded from the approved current database when required.
• Pilot-created waypoints must not be used to manually build instrument approach procedures.
• RNAV does not remove the need to follow ATC clearances, published altitudes, procedure notes, speed restrictions, and missed approach instructions.
• RNAV is a navigation method, not automatically an approach type or a guarantee of vertical guidance.
• RNAV approaches may have different minima such as LNAV, LNAV/VNAV, LPV, LP, or circling depending on the published chart and equipment.
• LNAV provides lateral guidance only and uses MDA.
• LNAV/VNAV and LPV provide vertical guidance when authorized and use DA.
• Always match the aircraft equipment, receiver annunciation, and published minima before using RNAV guidance.

3.10 Other Systems - Basic Principles and Use - RMI.

• RMI stands for Radio Magnetic Indicator.
• An RMI combines a rotating magnetic heading card with one or more radio navigation bearing pointers.
• The compass card shows aircraft magnetic heading at the top of the instrument.
• The bearing pointer head points toward the selected station.
• The pointer tail shows the reciprocal bearing from the station.
• An RMI can commonly display ADF bearing, VOR bearing, or both depending on aircraft equipment.
• With ADF selected, the RMI pointer points to the NDB station.
• With VOR selected, the RMI pointer points to the VOR station.
• RMI reduces mental math because magnetic bearing to the station can be read directly from the compass card.
• On a fixed-card ADF, magnetic bearing to the station equals heading plus relative bearing; an RMI does that display work for you.
• The aircraft heading is read at the top of the rotating card.
• Bearing to the station is read under the pointer head.
• Bearing from the station is read under the pointer tail.
• For VOR use, the pointer head shows bearing TO the VOR station and the tail shows the radial FROM the VOR.
• For ADF use, the pointer head shows bearing TO the NDB and the tail shows the reciprocal bearing FROM the NDB.
• RMI can help with station tracking, intercepts, position awareness, procedure turns, holds, and cross-checking other navigation displays.
• To home to a station using RMI, turn the aircraft until the pointer head is at the top of the card.
• To track to or from a station, apply wind correction instead of simply chasing the pointer.
• RMI does not provide course deviation like a CDI or HSI.
• RMI does not provide glidepath or vertical guidance.
• RMI does not by itself give distance to the station.
• A single RMI bearing gives a line of position, not an exact fix.
• A fix requires another bearing, radial, DME, GNSS position, or other position source.
• The RMI depends on correct heading information and valid radio navigation input.
• If the heading card is wrong, magnetic bearings read from the RMI will be wrong.
• If the selected radio source is not tuned, identified, or serviceable, the RMI pointer should not be trusted.
• Always confirm which source each pointer is using before interpreting the indication.

3.10 Other Systems - Basic Principles and Use - Horizontal Situation Indicator (HSI).

• HSI stands for Horizontal Situation Indicator.
• An HSI combines heading information with selected-course navigation guidance.
• The HSI shows aircraft heading on a rotating compass card.
• The course selector lets the pilot set a desired course, radial, localizer course, or RNAV course depending on the selected navigation source.
• The course deviation indicator shows whether the aircraft is left or right of the selected course.
• The CDI bar moves toward the side where the selected course is located.
• To correct course deviation, fly toward the CDI bar unless using an abnormal source or back-course situation requiring special interpretation.
• The heading at the top of the HSI is the aircraft's current magnetic heading.
• The selected course pointer shows the course the pilot has selected.
• The TO/FROM indicator shows whether the selected course is being flown toward or away from a VOR station when using VOR guidance.
• With VOR guidance, the HSI can show selected radial/course, CDI displacement, and TO/FROM information.
• With localizer guidance, the HSI shows left-right displacement from the localizer course.
• With ILS, the HSI may show localizer lateral guidance and a separate glide slope indicator may show vertical guidance.
• With RNAV or GNSS selected, the HSI can show lateral deviation from the active RNAV leg.
• HSI reduces workload because heading, selected course, and CDI are all displayed in one instrument.
• HSI makes wind correction and intercept angles easier to visualize than a basic VOR indicator.
• The HSI does not itself create navigation information; it displays information from the selected navigation source.
• The pilot must confirm the selected source, such as VOR, LOC, GPS, or RNAV.
• The pilot must tune, identify, and verify the navigation source when using conventional radio navigation.
• If the wrong source is selected, the HSI may display accurate-looking guidance to the wrong thing.
• If the heading input is wrong, the HSI compass card and course picture may be misleading.
• An HSI may reduce reverse-sensing confusion, but back-course operations still require correct setup and interpretation.
• For a localizer back course, set the published front course unless the aircraft equipment or procedure requires otherwise.
• HSI guidance does not replace ATC clearance, published procedures, altitude restrictions, minima, or missed approach instructions.
• A centred CDI means lateral course alignment only; it does not prove altitude, clearance, or landing legality.

3.10 Other Systems - Basic Principles and Use - Radio/radar altimeter.

• A radio altimeter and radar altimeter are the same basic type of instrument.
• A radio/radar altimeter measures height above the surface directly below the aircraft.
• It indicates height above ground level, not altitude above sea level.
• It works by transmitting a radio signal downward and measuring the time required for the signal to reflect back from the surface.
• The system converts signal travel time into vertical distance below the aircraft.
• The displayed value is radio altitude or radar altitude.
• Radio altitude is most useful close to the ground.
• A pressure altimeter shows altitude based on air pressure and altimeter setting.
• A radio/radar altimeter shows actual clearance above the reflecting surface below the aircraft.
• Radio/radar altitude is not affected by altimeter setting, pressure changes, or temperature errors in the same way as a pressure altimeter.
• Radio/radar altimeters are commonly used for low-level awareness, approach monitoring, automatic callouts, GPWS/TAWS functions, autopilot functions, and autoland systems.
• On some aircraft, decision height for low-visibility precision approaches may be referenced to the radio altimeter.
• A radio/radar altimeter does not provide terrain clearance ahead of the aircraft.
• It only measures the surface return below the aircraft at that moment.
• If terrain rises ahead, the radio/radar altimeter may not warn early enough by itself.
• Over sloping terrain, rough terrain, water, snow, vegetation, buildings, or uneven surfaces, the displayed height may change rapidly or be less stable.
• In steep bank or unusual attitude, the antenna may not be pointing straight down, so the indication may be misleading.
• Radio/radar altimeter information should be cross-checked with pressure altitude, charts, minima, vertical path, terrain awareness, and outside visual references when available.
• The radio/radar altimeter does not replace minimum IFR altitudes, published approach altitudes, DA, MDA, or obstacle clearance requirements.
• A failed or unreliable radio/radar altimeter can affect systems that depend on it, such as automatic callouts, GPWS/TAWS, autoland, and some flight director or autopilot modes.
• The pilot must know whether a particular approach, aircraft system, or operating procedure requires a serviceable radio/radar altimeter.

3.10 Other Systems - Basic Principles and Use - Flight Director system.

• A flight director is a cockpit guidance system that shows the attitude commands needed to follow selected flight modes.
• The flight director does not fly the aircraft by itself unless it is connected to an engaged autopilot.
• With the autopilot off, the pilot manually flies the aircraft to match the flight director command bars.
• With the autopilot on, the autopilot may follow the same flight director commands automatically.
• The flight director normally gives pitch and bank commands.
• Pitch commands may be based on altitude hold, vertical speed, airspeed, flight level change, glide slope, glide path, VNAV, or go-around mode.
• Bank or roll commands may be based on heading, track, VOR, localizer, GPS/RNAV, approach, or navigation capture modes.
• The command bars show where the aircraft should be flown, not necessarily where the aircraft is currently going.
• The pilot must always check the active flight director modes on the flight mode annunciator.
• Mode selection is critical because the flight director will command whatever mode is armed or active.
• Armed mode means the system is waiting to capture that guidance.
• Active mode means the system is currently commanding that guidance.
• A wrong mode can produce correct-looking but wrong guidance.
• The flight director uses inputs from attitude, heading, air data, navigation receivers, GNSS/RNAV, and approach guidance systems depending on aircraft equipment.
• Flight director guidance should be cross-checked with raw navigation data, attitude, heading, altitude, airspeed, vertical speed, and the published procedure.
• On an ILS, the flight director may command localizer and glide slope tracking when the correct approach mode is armed and captured.
• On an RNAV approach, the flight director may command lateral and vertical guidance only if the equipment and approach mode support it.
• The flight director does not remove the requirement to obey clearances, published altitudes, step-down fixes, DA, MDA, or missed approach procedures.
• The pilot must not blindly chase flight director bars if the aircraft is unstable, the mode is wrong, or the guidance does not match the procedure.
• A flight director can reduce workload, especially in IFR, but it can also increase risk if the pilot stops monitoring.

3.10 Other Systems - Basic Principles and Use - Surveillance Radar: Primary and Secondary.

• Surveillance radar helps ATC detect, identify, monitor, and separate aircraft.
• Primary Surveillance Radar is abbreviated PSR.
• Secondary Surveillance Radar is abbreviated SSR.
• PSR works by transmitting radio energy and receiving reflections from objects such as aircraft.
• PSR determines target position by measuring range and azimuth from reflected energy.
• PSR is passive from the aircraft's point of view because the aircraft does not need special equipment to be detected.
• PSR does not require a transponder.
• PSR normally shows a target position but not a selected squawk code or automatic altitude readout.
• PSR can detect some non-transponder aircraft, but radar coverage, terrain, range, target size, and system limitations still matter.
• Terminal Surveillance Radar is a short-range PSR used for terminal operations and may complement SSR.
• Precision Approach Radar is a high-definition short-range PSR used by controllers to assist some approaches.
• Airport Surface Detection Equipment is a high-definition PSR used to monitor aircraft and vehicles on manoeuvring areas.
• Weather radar is also a form of primary radar used to monitor hazardous weather.
• SSR works by interrogating an aircraft transponder and receiving a coded reply.
• SSR is cooperative surveillance because it depends on operating aircraft equipment.
• SSR determines range by timing the interval between interrogation and transponder reply.
• SSR provides operational advantages such as increased range, positive identification, and altitude information when altitude-encoding equipment is used.
• SSR cannot provide a position for an aircraft without an operating transponder.
• Mode A transponder replies provide the selected squawk code.
• Mode C transponder replies provide automatic pressure-altitude information.
• Mode S adds selective addressing and data-link capability.
• SSR en route surveillance may have a range of 200 NM or more.
• SSR transmits interrogations on 1030 MHz and receives replies on 1090 MHz.
• When SSR is used without primary radar, ATC may not be able to provide traffic information on aircraft without functioning transponders.
• Radar identification does not remove the pilot's responsibility for collision avoidance or terrain and obstacle clearance unless ATC is providing vectoring responsibility as applicable.
• ATS surveillance service can be terminated, and the pilot should continue normal navigation unless otherwise instructed.

3.10 Other Systems - Basic Principles and Use - Airborne weather radar.

• Airborne weather radar is an aircraft-mounted radar used to detect precipitation ahead of the aircraft.
• It helps pilots identify and avoid hazardous weather, especially thunderstorms and heavy precipitation.
• The radar antenna sends radio energy forward and receives energy reflected by precipitation particles.
• The display shows radar returns, not a direct picture of clouds, turbulence, lightning, or icing.
• Stronger returns usually indicate heavier precipitation and higher water content.
• Heavier precipitation is often associated with stronger turbulence, but radar does not directly measure turbulence.
• A weak return does not prove the air is safe.
• A strong return should be treated as a serious avoidance cue.
• Airborne radar is mainly a weather-avoidance tool, not a weather-penetration tool.
• Radar can miss hazards if the tilt, range, gain, or mode is set incorrectly.
• Tilt control is used to aim the radar beam up or down.
• If tilt is too high, the radar may overscan weather below the beam.
• If tilt is too low, the radar may paint ground returns and clutter the display.
• Range selection matters because a long range can make dangerous cells look small and less urgent.
• Shorter ranges are useful for tactical avoidance and approach to weather.
• Longer ranges are useful for strategic planning and early deviations.
• Gain affects receiver sensitivity and can change the apparent strength of returns.
• Automatic gain is normally used unless the aircraft procedure or equipment guidance calls for manual adjustment.
• Attenuation occurs when heavy precipitation absorbs or scatters radar energy, hiding weather behind it.
• A radar shadow behind a strong cell can be dangerous because the blank area may contain more severe weather.
• Do not assume that a gap between strong returns is safe, especially if the echoes are close together.
• Airborne radar does not reliably detect clear-air turbulence.
• Dry hail, cloud, snow, or ice crystals may not paint as strongly as heavy rain.
• Weather radar should be cross-checked with visual cues, ATC weather information, SIGMETs, AIRMETs, GFAs, radar imagery, lightning data, and PIREPs.
• The safest use of airborne weather radar is early avoidance with wide margins, not last-minute threading between cells.

3.10 Other Systems - Basic Principles and Use - Lightning detection equipment such as stormscope.

• Lightning detection equipment helps pilots identify areas of electrical activity associated with thunderstorms.
• Stormscope is a common example of airborne lightning detection equipment.
• The system detects electromagnetic signals produced by lightning discharges.
• It displays lightning strike information as symbols or cells relative to the aircraft.
• Lightning detection equipment shows electrical activity, not precipitation.
• Airborne weather radar shows precipitation returns; lightning detection equipment shows lightning activity.
• A thunderstorm may produce severe turbulence, hail, icing, wind shear, and lightning even when the display does not look dramatic.
• Frequent lightning usually suggests stronger convective activity.
• A cluster of strikes often indicates an active thunderstorm cell.
• A rapidly growing or moving cluster should be treated as hazardous.
• Lightning detection can help identify embedded thunderstorms that may not be visible outside.
• It can also detect electrical activity beyond the practical range or line-of-sight limitations of some visual cues.
• Lightning detection equipment is mainly an avoidance tool, not a penetration tool.
• It should be used with airborne weather radar, ATC weather information, SIGMETs, AIRMETs, GFAs, ground radar, satellite imagery, and PIREPs.
• Bearing and distance indications may be approximate and should not be treated as exact storm boundaries.
• Older strikes may remain displayed depending on the equipment mode and strike-aging logic.
• Clear or clear-all functions may help identify new strike activity and storm movement.
• Strike mode may show individual discharges; cell mode may group discharges into storm-cell areas.
• A lack of displayed strikes does not prove there is no thunderstorm hazard.
• Some storms may be dangerous before producing frequent detected lightning.
• Electrical noise, signal propagation, attenuation, or equipment limitations can affect interpretation.
• Lightning detection does not directly show turbulence, hail, icing, microbursts, or storm tops.
• Do not use a gap between strike clusters as proof of a safe route.
• Avoid thunderstorms with generous margins, especially severe cells, intense radar returns, embedded cells, and active lightning areas.
• The pilot must interpret lightning data as one part of the full weather picture.