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Instrument rating · ACS IR.II.B · lesson pack

Flight Instruments and Navigation Equipment

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Why this one matters

In cloud, the instruments are the only picture of the world, and each fails in its own way. Pilots who know how a blocked static port or a dying vacuum pump looks catch it early and switch to what still works. Pilots who don’t follow a failed instrument into an upset.

1 · Know these cold

  • •Pitot-static: the airspeed indicator uses pitot and static pressure; the altimeter and vertical speed indicator use static only.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • •Blocked static port: the altimeter freezes, the VSI shows zero, and the airspeed reads low in a climb and high in a descent. Use alternate static.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • •Gyros: the attitude and heading indicators are often vacuum-driven; the turn coordinator is often electric. Know which on your airplane so one failure doesn’t take them all.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • •To use a VOR under IFR, it must have been checked within the preceding 30 days: ±4° on a VOT, a repair station's test signal or a ground checkpoint; ±6° on an airborne checkpoint or a radial over a prominent landmark (preferably more than 20 nm out); 4° between two independent receivers. Log the date, place, bearing error and your signature. Out of tolerance, it isn't usable for IFR.(14 CFR 91.171)
  • •GPS for IFR must be installed and approved (AFM supplement). A tablet or handheld is for awareness, not IFR navigation.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
  • •GPS approaches need a current database. A non-WAAS unit with fault detection and exclusion also needs a preflight RAIM prediction for your arrival, and may plan a GPS approach at the destination or the alternate, not both (LNAV or circling minimums at the alternate). WAAS units don't have that either-or limit.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
  • •On a glass panel, know the reversionary modes and the standby instruments before you need them.(Advanced Avionics Handbook (FAA-H-8083-6))

2 · The lesson

Flight instruments and how they fail
  • Pitot blocked, drain open: airspeed drops to zero. Pitot and drain blocked: the airspeed indicator acts like an altimeter, rising in a climb.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • Static blocked: altimeter frozen, VSI at zero, airspeed right only at the blockage altitude (reading low in a climb above it, high in a descent below it).(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • Alternate static in most unpressurized airplanes draws lower cabin pressure: the altimeter reads higher, the airspeed faster, and the VSI shows a brief climb before settling. The direction depends on the airplane; use the POH correction table.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments; Your airplane's POH/AFM and supplements)
  • Pitot and drain both blocked: the airspeed over-reads in a climb, under-reads in a descent, and doesn't respond to speed changes in level flight. Fly pitch and power and cross-check GPS groundspeed.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • Gyros: know which of yours are vacuum, which electric. The heading indicator precesses: realign it with the compass about every 15 minutes in straight, level flight. A failing vacuum pump makes the attitude and heading indicators drift slowly, which is hard to notice: watch the suction gauge, cross-check, cover the failed instruments and fly partial panel.(Instrument Flying Handbook (FAA-H-8083-15B), Flight Instruments)
  • Electrical failure: on battery alone you may have about 30 minutes, depending on the battery and the load; shed everything not needed, and expect the electric instruments, navigators and radios to fail as it runs down. Know which instruments are electric in your airplane, tell ATC early and plan the nearest approach.(Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Aircraft Systems; Your airplane's POH/AFM and supplements)
  • Glass panels: an AHRS gives attitude and heading; an air data computer takes the same pitot and static inputs, so a blocked pitot or static port fails the glass the same way. A red X means that parameter is invalid. Know the reversionary mode and the independent standby attitude indicator.(Advanced Avionics Handbook (FAA-H-8083-6))
  • Magnetic compass errors: deviation (use the card), variation, and, in the northern hemisphere, acceleration errors on east and west headings (ANDS: accelerate north, decelerate south) and turning errors on north and south headings (UNOS: undershoot north, overshoot south). It reads correctly only in straight, level, unaccelerated flight.(Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Flight Instruments)
  • Transponder with Mode C (91.215) and ADS-B Out (91.225(d)) are each required in Class A, B and C; within 30 nm of Class B primary airports from the surface to 10,000 MSL; above Class B and C up to 10,000 MSL; and in Class E at and above 10,000 MSL except at or below 2,500 AGL. ADS-B Out adds Class E over the Gulf of Mexico at and above 3,000 MSL within 12 nm of the coast.(14 CFR 91.215, 91.225)
  • Rules that decide whether the airplane may fly IFR: 91.205(d) lists the IFR equipment; 91.213 governs inoperative equipment; 91.411 requires the altimeter, static system and altitude reporting tested within 24 calendar months for IFR in controlled airspace; 91.413 bars using a transponder not tested within 24 calendar months.(14 CFR 91.205(d), 91.213, 91.411, 91.413)
Navigation equipment
  • VOR: tune, identify by Morse code, and check it per 91.171 within 30 days for IFR. DME gives slant range: overhead a station at 6,000 feet AGL it reads about 1 nm; the error is small when you're 1 nm or more away for every 1,000 feet of altitude.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
  • ILS: the localizer is about 2.5° either side at full scale, roughly four times as sensitive as a VOR; identify it by Morse code. The back course reverse-senses on a CDI. The glideslope has false glideslopes above the real one: intercept it from below. Marker beacons where installed.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
  • LPV is an approach with vertical guidance (APV) flown to a DA, not a precision approach; the precision approaches are ILS (and GLS where authorized). That matters for alternate minimums.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
  • GPS and WAAS: WAAS improves accuracy and integrity and allows LPV approaches. Non-WAAS GPS needs a RAIM prediction and may use a GPS approach at the destination or the alternate, not both.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
  • Only equipment installed and approved for IFR counts. The AFM supplement says what the navigator is approved for.(Your airplane's POH/AFM and supplements)
  • Load approaches from the database only; never build one by hand. Check the database is current before departure.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
Automation and the electronic flight bag
  • Automation: preflight test the autopilot, know how to engage and disconnect it, and read the annunciator after every selection: armed modes (white) are waiting; active modes (green) are flying. Verify the airplane does what the annunciator says; if it doesn't, or the system fails, disconnect and hand-fly on raw data.(Advanced Avionics Handbook (FAA-H-8083-6); Your airplane's POH/AFM and supplements)
  • An EFB can replace paper charts if its data is current. For ordinary Part 91 flying, a backup (a second device or paper) is recommended risk management, not a regulation.(AC 91-78A, Use of Electronic Flight Bags)
  • An EFB moving map and weather are for awareness; they don’t replace the installed navigator or ATC.(AC 91-78A, Use of Electronic Flight Bags)

Want it all on one page, with scenarios? Read the full lesson.

3 · Say it out loud

Answer each one out loud, then check yourself and mark how it went.

  1. Remember Recall it

    “Which instruments use only static pressure?”

  2. Understand Explain why

    “Why is a vacuum failure hard to catch?”

  3. Apply Use it on a flight

    “In cloud, the altimeter hasn’t moved for a while and the VSI is at zero, but the airspeed is rising. What do you do?”

4 · Common mistakes

  • Not identifying the navaid.

    You may track the wrong or a failed station.

    Instead: Listen to the Morse code every time.

  • Trusting one instrument.

    Failures look normal at first.

    Instead: Cross-check all of them.

  • Using a tablet as the IFR navigator.

    It isn’t approved.

    Instead: Navigate on installed, approved equipment.

5 · Quick check

Answer, then reveal. Flag anything you want to see again.

  1. 1. VOR check tolerance on a VOT?

  2. 2. What four things go in the VOR check log?

  3. 3. Static port blocked: what does the airspeed indicator do in a descent?

  4. 4. What does a non-WAAS GPS need for an approach?

  5. 5. Accelerating on an east heading, the compass shows a turn to the...?

  6. Scenario6. The attitude indicator shows a slow bank, but the turn coordinator and heading are steady. What do you do?

Trained it? Now prove it: practice flight instruments and navigation equipment out loud with our examiner.

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Connect it

One situation that runs across this lesson and its neighbors in the same ACS area. Decide first, then check.

Connect it · Preflight Procedures

In cloud near freezing, airspeed starts falling toward zero while attitude, power and altitude are unchanged. Later the attitude indicator slowly tilts while the turn coordinator shows wings level.

Diagnose both and connect them to the checks before flight. Decide, then see the worked answer

Airspeed falling toward zero with nothing else changing points to a blocked pitot inlet, likely ice, with the drain hole still open: the pressure in the line bleeds away, so the reading falls. (If the inlet and the drain are both blocked, the indicator acts like an altimeter instead, rising in a climb and falling in a descent.) Pitot heat should already be on in visible moisture near freezing. Turn it on, but don't count on the reading coming back: fly a known attitude and power setting, treat the airspeed as unreliable, tell ATC, and get out of the icing. Diagnose the attitude indicator by its power source. Check the suction gauge: low suction means a vacuum failure, so distrust both vacuum gyros, the attitude and heading indicators in a typical trainer, and cover them. Fly partial panel on the turn coordinator, the magnetic compass, and the altimeter, VSI and airspeed. Which instruments run on vacuum and which on electric power is airplane-specific, so know yours. Tell ATC and request a clearance that gets you out: vectors or a route to VFR conditions or the nearest suitable airport. Declare an emergency under 91.3 only if you need to deviate from a clearance. Both trace back to the instrument flight deck check, done in phases. Before start: instruments set and checked. After start: give the gyros about 5 minutes to spin up, check suction in the normal range (typically 4.5 to 5.5 inches of mercury), and check the pitot heat. While taxiing: set the heading indicator to the compass, and check the turn coordinator deflects in turns and the attitude indicator stays steady.

IFH (FAA-H-8083-15B), Flight Instruments; 14 CFR 91.3

Brings together: Aircraft Systems Related to Instrument Flight Rules (IFR) Operations · Aircraft Flight Instruments and Navigation Equipment · Instrument Flight Deck Check

Teaching this? The instructor lesson plan →

Study aid, not FAA guidance. Sources: Instrument Flying Handbook (FAA-H-8083-15B); Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); Advanced Avionics Handbook (FAA-H-8083-6); Aeronautical Information Manual (AIM); 14 CFR; Instrument Rating ACS (FAA-S-ACS-8C). Checked against current sources 2026-11-13.