AM Troubleshooting & Diagnostics 2 — Questions and Answers
Question 1: An aircraft engine experiences intermittent power loss only at high altitude. Which system is the most likely cause?
- Fuel boost pump failure
- Mixture control or fuel metering unit malfunction (Correct answer)
- Starter motor degradation
- Oil pressure relief valve sticking
Correct answer: Mixture control or fuel metering unit malfunction
Altitude-related power loss typically indicates a fuel metering or mixture issue since fuel-air ratio requirements change significantly with altitude.
Question 2: During run-up, a magneto drop is 175 RPM on the left magneto and 50 RPM on the right. What does this indicate?
- Both magnetos are serviceable
- The left magneto or its spark plugs have a problem (Correct answer)
- The right magneto is faulty
- The timing is advanced on both magnetos
Correct answer: The left magneto or its spark plugs have a problem
An excessive drop on one magneto indicates a fault in that magneto, its leads, or the spark plugs it fires; the right magneto's low drop is normal.
Question 3: A hydraulic actuator moves slower than normal but maintains full travel. Which fault is most likely?
- Actuator mechanical seizure
- Restriction in the hydraulic line or internal bypass/wear (Correct answer)
- Loss of hydraulic fluid pressure source
- Incorrect actuator sizing
Correct answer: Restriction in the hydraulic line or internal bypass/wear
Slow but full-travel movement suggests a flow restriction or internal leakage allowing the actuator to eventually reach full extension.
Question 4: When troubleshooting an avionics unit that shows no display, the FIRST step per standard procedure is to:
- Replace the unit with a serviceable spare
- Check circuit breakers and power supply to the unit (Correct answer)
- Remove and bench-test the unit
- Update the software/firmware
Correct answer: Check circuit breakers and power supply to the unit
Always verify power and circuit breaker status before condemning or removing any avionics unit.
Question 5: An aircraft landing gear indicates 'gear up' in the cockpit but the red warning light remains illuminated. What should be investigated first?
- Hydraulic system pressure loss
- Proximity sensor or micro-switch alignment on the gear (Correct answer)
- Cockpit indicator bulb failure
- Landing gear door sequencing valve
Correct answer: Proximity sensor or micro-switch alignment on the gear
A disagreement between the position indicator and the warning light often points to a misaligned or faulty proximity sensor or limit switch.
Question 6: Excessive oil consumption with blue smoke from the exhaust on an aircraft piston engine most likely indicates:
- Fuel contamination in the oil
- Worn piston rings or cylinder wall glazing (Correct answer)
- Over-serviced oil quantity
- Clogged oil cooler
Correct answer: Worn piston rings or cylinder wall glazing
Blue exhaust smoke indicates burning oil, which enters the combustion chamber through worn rings or glazed cylinder walls.
Question 7: A pitot-static system leak check reveals the altimeter drops more than the allowable rate. The CORRECT action is to:
- Recalibrate the altimeter to compensate
- Locate and repair the leak, then re-check the system (Correct answer)
- Seal the pitot probe inlet and re-test
- Log the discrepancy and continue operations
Correct answer: Locate and repair the leak, then re-check the system
FAR/maintenance standards require that any leak exceeding the allowable rate must be repaired and the system re-tested before the aircraft is returned to service.
AM Troubleshooting & Diagnostics 2
An aircraft engine experiences intermittent power loss only at high altitude.
Which system is the most likely cause?