Airframe Mechanic Certification Powerplant Systems & Maintenance 2 — Questions and Answers
Question 1: What is the primary purpose of an engine's magneto impulse coupling?
- Advance ignition timing at cruise
- Retard ignition timing during starting to prevent kickback (Correct answer)
- Increase spark intensity at high altitude
- Synchronize dual magnetos
Correct answer: Retard ignition timing during starting to prevent kickback
Impulse couplings retard and then rapidly release to produce a hot spark at low engine RPM during starting, preventing kickback.
Question 2: When inspecting a turbine engine's compressor blades, a nick that exceeds allowable limits requires:
- Blending with a fine file and returning to service
- Immediate replacement of the blade
- Repair per the manufacturer's structural repair manual (Correct answer)
- Polishing and a 10-hour check flight
Correct answer: Repair per the manufacturer's structural repair manual
Damage exceeding allowable limits must be repaired per the manufacturer's structural repair manual or the engine must be removed.
Question 3: In a reciprocating engine, detonation differs from pre-ignition in that detonation:
- Occurs before the spark plug fires
- Is caused by a hot spot in the combustion chamber
- Results from fuel-air mixture auto-igniting after normal spark ignition (Correct answer)
- Always causes immediate engine failure
Correct answer: Results from fuel-air mixture auto-igniting after normal spark ignition
Detonation is explosive auto-ignition of the end charge after normal spark ignition, whereas pre-ignition occurs before the spark plug fires.
Question 4: Which statement about turbine engine oil systems is correct?
- Oil pressure should be checked only at idle
- Most turbine engines use a dry sump oil system (Correct answer)
- Oil consumption in turbines is typically higher than reciprocating engines
- Turbine engines use the same oil grades as reciprocating engines
Correct answer: Most turbine engines use a dry sump oil system
Turbine engines use a dry sump system where oil is stored in a separate tank rather than the engine sump.
Question 5: A fuel control unit (FCU) on a turbine engine primarily schedules fuel flow based on:
- Pilot throttle position only
- Compressor inlet temperature and pressure, throttle position, and RPM (Correct answer)
- Exhaust gas temperature alone
- Fuel tank quantity and ambient temperature
Correct answer: Compressor inlet temperature and pressure, throttle position, and RPM
The FCU uses multiple inputs including compressor inlet conditions, throttle position, and RPM to schedule the correct fuel flow.
Question 6: When performing a compression check on a reciprocating engine cylinder, a reading of 72/80 indicates:
- The cylinder is serviceable per most manufacturer limits (Correct answer)
- The cylinder must be immediately overhauled
- The reading is invalid and must be retested
- The piston rings are definitely failed
Correct answer: The cylinder is serviceable per most manufacturer limits
A differential compression ratio of 72/80 (90%) is typically within the acceptable range of 60/80 or greater per most manufacturers.
Question 7: What does EGT (Exhaust Gas Temperature) measure in a turbine engine?
- Combustion chamber inlet temperature
- Temperature of exhaust gases at a specified turbine stage (Correct answer)
- Compressor discharge temperature
- Turbine inlet temperature directly
Correct answer: Temperature of exhaust gases at a specified turbine stage
EGT measures the temperature of exhaust gases at a specified point aft of the turbine section, used as an indicator of engine health and limits.
