20 Instruments, Communication & Navigation Practice Questions & Answers

1. 1. Under 14 CFR 91.411, which test on an aircraft to be operated IFR in controlled airspace may a certificated mechanic holding an airframe rating perform?

   • A.The altimeter instrument test and inspection only
   • B.The altimeter and static pressure system tests together
   • C.The static pressure system test and inspection only✓ Answer
   • D.The transponder and altitude reporting correlation test

   14 CFR 91.411(b)(3) limits a certificated mechanic with an airframe rating to tests and inspections of the static pressure system. The altimeter instrument test must be performed by the aircraft manufacturer or by an appropriately rated certificated repair station, because calibrating the instrument itself is beyond mechanic privileges.

   Source: 14 CFR 91.411(b)(3)Report a problem with this question

2. 2. An unpressurized aircraft's static system is evacuated until the altimeter indicates 1,000 feet, then sealed and held for 1 minute without further pumping. What is the maximum allowable leakage?

   • A.A loss of indicated altitude not exceeding 500 feet
   • B.A loss of indicated altitude not exceeding 50 feet
   • C.A loss of indicated altitude not exceeding 200 feet
   • D.A loss of indicated altitude not exceeding 100 feet✓ Answer

   14 CFR part 43 Appendix E prescribes this proof test for unpressurized aircraft: after evacuating the system to an indication about 1,000 feet above field elevation, the loss of indicated altitude must not exceed 100 feet in 1 minute. A greater loss means the system leaks and cannot be relied on to give accurate altitude and airspeed indications.

   Source: 14 CFR part 43, Appendix E, paragraph (a)Report a problem with this question

3. 3. During the altimeter system test, what is the maximum difference allowed between the altitude reported by the automatic pressure altitude reporting equipment and the altitude displayed on the altimeter?

   • A.250 feet
   • B.400 feet
   • C.125 feet✓ Answer
   • D.75 feet

   Part 43 Appendix E requires that the automatic pressure altitude reporting output correspond to the altitude displayed on the altimeter within 125 feet. The encoder always references 29.92 in. Hg, so ATC applies the local setting; a correspondence error larger than 125 feet would place the aircraft at an incorrect altitude on the controller's display.

   Source: 14 CFR part 43, Appendix E, paragraph (c)Report a problem with this question

4. 4. A static line becomes disconnected inside the pressurized cabin of an aircraft in flight. How will the altimeter and the airspeed indicator read?

   • A.The altimeter higher and the airspeed lower
   • B.The altimeter lower and the airspeed higher
   • C.Both will indicate higher than normal
   • D.Both will indicate lower than normal✓ Answer

   Cabin pressure in a pressurized aircraft is higher than the outside static pressure, so the instruments now sense too much pressure: the altimeter's aneroid is compressed and shows less altitude, and the higher pressure in the airspeed case reduces the differential across the diaphragm, so airspeed reads low. The vertical speed indicator momentarily shows a descent and then returns to zero.

   Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 10Report a problem with this question

5. 5. After a magnetic compass has been swung and compensated, what is the maximum deviation permitted on any heading?

   • A.5 degrees
   • B.10 degrees✓ Answer
   • C.15 degrees
   • D.2 degrees

   Airworthiness standards and AC 43.13-1 limit residual compass deviation to 10 degrees on any heading after compensation, because larger errors would make the heading reference unreliable for navigation. The remaining deviation is recorded every 30 degrees on a correction card that is dated, signed, and mounted in view of the pilot.

   Source: AC 43.13-1, Ch. 12; 14 CFR 23.1327Report a problem with this question

6. 6. Which magnetic compass error does the mechanic correct by adjusting the compensating magnets during a compass swing?

   • A.Variation between magnetic north and true geographic north
   • B.Oscillation error caused by turbulence and rough air in flight
   • C.Northerly turning error caused by magnetic dip at the poles
   • D.Deviation caused by aircraft ferrous metal and electrical fields✓ Answer

   Deviation is caused by magnetic fields originating in the aircraft itself, so it can be reduced with the north-south and east-west compensating magnets. Variation is the angular difference between magnetic and true north at a geographic location and is a property of the earth, so no adjustment in the aircraft can remove it.

   Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 10Report a problem with this question

7. 7. Which gyroscopic property allows a turn-and-slip indicator to sense the aircraft's rate of turn?

   • A.Precession of the spinning gyro rotor✓ Answer
   • B.Magnetic dip acting on the gyro rotor
   • C.Rigidity in space of the gyro rotor
   • D.Centrifugal force acting on the gyro rotor

   A turn indicator's gyro is mounted so that yawing the aircraft applies a force to the spinning rotor; precession makes the rotor tilt at a rate proportional to the rate of turn, which drives the pointer. Attitude indicators and directional gyros instead use rigidity in space, and the ball is a simple inclinometer, not a gyroscopic element.

   Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 10Report a problem with this question

8. 8. An airplane's vacuum-driven gyro instruments are sluggish and the suction gauge reads below the value specified for the system. What is the most likely cause?

   • A.A clogged central air filter restricting system airflow✓ Answer
   • B.A relief valve adjusted to give excessive system suction
   • C.An engine-driven pump turning above its rated speed
   • D.Instrument filters that were replaced at the last inspection

   The gyros are driven by air drawn through a central filter, so a filter loaded with dust restricts the flow, slows the rotors, and shows up as low suction and lazy or unstable indications. Excessive suction or an overspeeding pump would raise the gauge reading and overspeed the rotors, not lower the indication.

   Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 10; AC 43.13-1, Ch. 12Report a problem with this question

9. 9. On an inspection you find that the white slippage mark on a range-marked instrument no longer lines up across the glass and the case. What does this indicate?

   • A.The instrument case is unbonded and is generating radio interference
   • B.The instrument has been overpressured and the diaphragm has ruptured
   • C.The cover glass has rotated and the range markings are invalid✓ Answer
   • D.The panel shock mounts have hardened and are transmitting vibration

   When range markings are applied to the cover glass, a white slippage mark is extended from the glass onto the case so that any rotation of the glass is immediately visible. A broken or misaligned mark means the markings no longer align with the dial calibrations and must be repositioned before the instrument is returned to service.

   Source: AC 43.13-1, Ch. 12Report a problem with this question

10. 10. Why may the leads of a cylinder head temperature thermocouple system not be shortened or replaced with a different wire?

    • A.The leads are calibrated to a specific total circuit resistance✓ Answer
    • B.The leads carry the excitation voltage supplied to the indicator
    • C.The leads must match the length of the ignition harness runs
    • D.The leads are shielded to suppress radio frequency interference

    A thermocouple generates a small voltage proportional to the temperature difference between its hot and cold junctions, and the indicator is calibrated for a fixed total resistance of the lead pair. Changing the length, cross-section, or material alters that resistance and the current through the meter, producing a false temperature indication.

    Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 10Report a problem with this question

11. 11. A capacitance-type fuel quantity indicating system measures the fuel in the tank in terms of what quantity, and by what means?

    • A.Volume, because a float arm moves a wiper along a variable resistor
    • B.Volume, because the tank probes change resistance as fuel covers them
    • C.Weight, because the fuel acts as the dielectric of the tank probes✓ Answer
    • D.Weight, because the tank probes sense the pressure of the fuel column

    The tank units are concentric-plate capacitors, open top and bottom, wired in parallel; fuel and air form the dielectric, and because the dielectric constant follows fuel density the bridge output is proportional to mass rather than volume. Indicating by weight is why the system is preferred on large aircraft, since it compensates for density and attitude changes and has no moving parts.

    Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 10Report a problem with this question

12. 12. Under 14 CFR part 43, how is the calibration and repair of an aircraft instrument classified?

    • A.As preventive maintenance, which the pilot owner may perform
    • B.As a minor alteration, which requires only a maintenance record entry
    • C.As a major repair, which a certificated mechanic may not perform✓ Answer
    • D.As a minor repair, which any certificated mechanic may perform

    Appendix A to part 43 lists calibration and repair of instruments among appliance major repairs, so the work must go to an appropriately rated repair station or the manufacturer. A certificated mechanic may still remove, install, inspect, and functionally check an instrument, but may not open it up to repair or recalibrate it.

    Source: 14 CFR part 43, Appendix A(b)Report a problem with this question

13. 13. Under 14 CFR 91.413, who is authorized to perform the required ATC transponder tests and inspections?

    • A.A certificated mechanic who also holds an inspection authorization
    • B.A certificated mechanic holding both airframe and powerplant ratings
    • C.A certificated repairman employed by an approved avionics shop
    • D.A certificated repair station holding an appropriate radio class rating✓ Answer

    Section 91.413(c) allows the tests to be done only by a certificated repair station with the appropriate radio class rating, by a holder of a continuous airworthiness maintenance program, or by the aircraft manufacturer if it installed the transponder. Because the test requires calibrated interrogation and reply measurements, mechanic and inspection-authorization privileges do not extend to it.

    Source: 14 CFR 91.413(c)Report a problem with this question

14. 14. Under 14 CFR 91.207, when must the battery of an emergency locator transmitter be replaced or recharged?

    • A.After one cumulative hour of use, or at 50 percent of useful life✓ Answer
    • B.After one cumulative hour of use, or at 75 percent of useful life
    • C.After two cumulative hours of use, or at 50 percent of useful life
    • D.At every 12 calendar month inspection, or after any inadvertent activation

    Section 91.207(c) requires replacement or recharge when the transmitter has been in use for more than 1 cumulative hour or when 50 percent of the battery's useful life, or useful life of charge, has expired. The new expiration date must be legibly marked on the outside of the transmitter and entered in the aircraft maintenance record so remaining capacity can always be verified.

    Source: 14 CFR 91.207(c)Report a problem with this question

15. 15. Under 14 CFR 91.207, how often must a required emergency locator transmitter be inspected for installation, battery corrosion, control operation, and antenna radiation?

    • A.Every 6 calendar months
    • B.Every 24 calendar months
    • C.Every 12 calendar months✓ Answer
    • D.At each 100-hour inspection

    Section 91.207(d) requires the ELT to be inspected every 12 calendar months for proper installation, battery corrosion, operation of the controls and crash sensor, and the presence of a sufficient signal radiated from its antenna. The 24-calendar-month interval belongs to the static system, altimeter, and transponder checks of 91.411 and 91.413.

    Source: 14 CFR 91.207(d)Report a problem with this question

16. 16. On what frequency do the outer, middle, and inner marker beacons of an ILS transmit?

    • A.All three transmit on the same frequency, 108 MHz
    • B.Each transmits on a frequency paired with the localizer
    • C.Each transmits on a separate frequency in the VHF band
    • D.All three transmit on the same frequency, 75 MHz✓ Answer

    All ILS marker beacons transmit on 75 MHz in a narrow fan beam directed straight up, and the airborne receiver is fixed-tuned to that frequency and fed by a belly-mounted antenna. The markers are distinguished by their modulation tone and lamp instead: the outer gives 400 Hz dashes with a blue light, the middle 1300 Hz dot-dash with amber, and the inner 3000 Hz dots with white.

    Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 11Report a problem with this question

17. 17. Which statement about the localizer and glide slope transmitters of an ILS is correct?

    • A.The localizer is VHF and the glide slope UHF, and they are frequency paired✓ Answer
    • B.The localizer is UHF and the glide slope VHF, and they are frequency paired
    • C.Both operate in the VHF band, and each must be tuned separately by the crew
    • D.Both operate in the UHF band, and each must be tuned separately by the crew

    The localizer occupies the odd tenths of 108.10 to 111.95 MHz in the VHF navigation band and provides lateral guidance, while the glide slope operates in the UHF band near 329 to 335 MHz and provides vertical guidance. The two are paired at the transmitting facility, so selecting the localizer frequency automatically tunes the matching glide slope receiver.

    Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 11Report a problem with this question

18. 18. A quarter-wave VHF communication blade antenna is being installed on a composite airplane. What additional provision must be made?

    • A.A second blade antenna mounted opposite for phase balance
    • B.A ground plane of foil or radial wires under the antenna base✓ Answer
    • C.A quarter-wave matching stub connected to the antenna base
    • D.A dielectric spacer installed between the antenna and the skin

    A quarter-wave Marconi antenna radiates against the conductive skin, which acts as the missing half of the dipole; a composite or fabric structure provides no such conductive surface. A ground plane of metal foil, a plate, or radial wires must therefore be built in beneath the antenna base, or the antenna will be badly mismatched and its range will be poor.

    Source: AC 43.13-1, Ch. 11; FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 11Report a problem with this question

19. 19. What is the purpose of the static discharge wicks installed on an aircraft's trailing edges?

    • A.To bleed off precipitation static that interferes with radio reception✓ Answer
    • B.To carry the current of a direct lightning strike around the airframe
    • C.To equalize potential between dissimilar metals and prevent corrosion
    • D.To provide the ground return path for the aircraft electrical system

    Friction with precipitation and dust charges the airframe, and the discharge builds broadband noise that degrades communication and navigation reception. The wicks present sharp, high-resistance points at the trailing edges that bleed the charge into the airstream quietly; they are not lightning protection, and an inspection checks base security, bonding, tip erosion, and the exposed inner braid.

    Source: AC 43.13-1, Ch. 11Report a problem with this question

20. 20. What precaution must be observed before operating an aircraft's weather radar on the ground?

    • A.Confirm the radome is removed so the antenna sweep can be observed directly
    • B.Confirm the transponder is in standby so the radar returns are not corrupted
    • C.Confirm the beam is clear of personnel and that no refueling is in progress✓ Answer
    • D.Confirm the aircraft is inside a hangar so the walls will contain the beam

    Weather radar radiates high-energy microwave power that can injure tissue, with the eyes and testes most at risk, and can ignite fuel vapor or induce arcing near fueling operations. The set may only be operated with the beam pointed at a clear area away from people, buildings, and reflecting surfaces, and never during refueling or in a hangar unless radar-absorbing material is used.

    Source: FAA-H-8083-31 Aviation Maintenance Technician Handbook (Airframe), Ch. 11Report a problem with this question

Practice questions based on the Aviation Mechanic Airman Certification Standards (FAA-S-ACS-1), 14 CFR parts 43, 65, and 91, and the FAA Aviation Maintenance Technician Handbook—Airframe (FAA-H-8083-31). This site is not affiliated with or endorsed by the Federal Aviation Administration. This bank covers the AIRFRAME written test only; the General and Powerplant written tests and the oral and practical tests are separate. Torque values, cable tensions, inflation pressures, servicing quantities, wear limits, and repair criteria always come from the manufacturer's current maintenance data, the structural repair manual, and the applicable airworthiness directives — never from a practice test. Confirm current eligibility and testing requirements with the FAA before you test. About the A&P mechanic certificate →