Airframe Mechanic Certification Powerplant Systems & Maintenance 4 — Questions and Answers
Question 1: What is the function of a propeller governor?
- Limit maximum propeller RPM by feathering
- Maintain a selected RPM by varying propeller pitch (Correct answer)
- Prevent propeller overspeed by cutting fuel
- Control propeller de-ice heating cycles
Correct answer: Maintain a selected RPM by varying propeller pitch
The propeller governor maintains a pilot-selected RPM by increasing or decreasing blade pitch as engine power or airspeed changes.
Question 2: Carburetor icing most commonly forms:
- Only at ambient temperatures below 0°C
- At temperatures between approximately -7°C and 21°C with high humidity (Correct answer)
- Only during flight above 10,000 feet MSL
- Only when the mixture is set to rich
Correct answer: At temperatures between approximately -7°C and 21°C with high humidity
Carburetor ice can form at temperatures between -7°C and 21°C (20°F–70°F) when humidity is high due to fuel evaporation and venturi cooling effects.
Question 3: An oil analysis report showing a sudden spike in iron particles most likely indicates:
- Normal oil oxidation
- Wear or damage in ferrous engine components such as cylinder walls or gears (Correct answer)
- Contamination from the fuel system
- Excessive water in the oil
Correct answer: Wear or damage in ferrous engine components such as cylinder walls or gears
Iron particles in oil analysis indicate wear or damage to ferrous metal engine components and warrant investigation before further flight.
Question 4: What happens to mixture requirements as altitude increases in a non-turbocharged reciprocating engine?
- More fuel is required to maintain the correct ratio
- Mixture must be leaned because air density decreases (Correct answer)
- Mixture must be enriched because fuel vaporizes faster
- Altitude has no effect on mixture setting
Correct answer: Mixture must be leaned because air density decreases
As altitude increases, air density decreases so less air enters the engine, requiring the mixture to be leaned to maintain the proper fuel-air ratio.
Question 5: A turbine engine's N1 speed refers to:
- High-pressure compressor and turbine spool speed
- Low-pressure compressor (fan) and turbine spool speed (Correct answer)
- Propeller RPM on a turboprop
- Accessory gearbox speed
Correct answer: Low-pressure compressor (fan) and turbine spool speed
N1 represents the rotational speed of the low-pressure spool, which includes the fan (in turbofans) and associated low-pressure turbine stages.
Question 6: When must a reciprocating engine be run on the ground before an oil change is due, according to best maintenance practice?
- Never — always change oil cold
- Warm the engine to operating temperature to suspend contaminants in the oil before draining (Correct answer)
- Run for exactly 30 minutes at full power
- Only warm-up is required if oil is over 200 hours old
Correct answer: Warm the engine to operating temperature to suspend contaminants in the oil before draining
Warming the engine to operating temperature suspends contaminants and sludge in the oil so they drain out with the old oil rather than remaining in the engine.
Question 7: Thrust reversers on turbine-powered aircraft are primarily used to:
- Supplement braking on landing rollout (Correct answer)
- Provide reverse thrust for pushback from the gate
- Reduce approach speed below normal
- Allow steep descents without speed increase
Correct answer: Supplement braking on landing rollout
Thrust reversers redirect engine exhaust forward to provide deceleration assistance during landing rollout, reducing brake wear and stopping distance.
Airframe Mechanic Certification Powerplant Systems & Maintenance 4
What is the function of a propeller governor?