Airframe Mechanic Certification Powerplant Systems & Maintenance 3 — Questions and Answers
Question 1: An aircraft reciprocating engine is running rough. You find one magneto drops 175 RPM during the mag check. This most likely indicates:
- The timing on that magneto is slightly advanced
- A fouled spark plug or failed ignition lead on that magneto's circuit (Correct answer)
- Normal operation within limits
- The other magneto has failed
Correct answer: A fouled spark plug or failed ignition lead on that magneto's circuit
An excessive RPM drop on one magneto suggests a fouled plug or defective ignition lead is preventing complete combustion on that magneto alone.
Question 2: What is the purpose of a turbine engine's bleed air system?
- Cool the combustion liner only
- Provide air for cabin pressurization, anti-icing, and engine starting (Correct answer)
- Increase compressor pressure ratio
- Prevent compressor stall exclusively
Correct answer: Provide air for cabin pressurization, anti-icing, and engine starting
Bleed air extracted from the compressor stages supplies pressurization, anti-icing, pneumatic engine starting, and other aircraft systems.
Question 3: The P-lead wire on a magneto, when grounded, causes the magneto to:
- Produce maximum spark output
- Be disabled (switched off) (Correct answer)
- Advance ignition timing
- Activate the impulse coupling
Correct answer: Be disabled (switched off)
Grounding the P-lead shorts the primary circuit of the magneto, preventing it from firing and effectively turning it off.
Question 4: During engine run-up, which condition indicates a possible induction system air leak on a fuel-injected reciprocating engine?
- Higher than normal fuel flow at idle
- Engine runs rough and mixture response is abnormal (Correct answer)
- Oil pressure fluctuations
- Magneto drop exceeds 25 RPM
Correct answer: Engine runs rough and mixture response is abnormal
An induction leak introduces unmetered air, causing rough running and abnormal mixture response because the fuel control cannot account for the extra air.
Question 5: A turbine engine compressor stall is best described as:
- Complete loss of engine power
- Disruption of airflow through the compressor causing pressure reversal (Correct answer)
- Over-temperature of the turbine section
- Failure of the high-pressure compressor shaft
Correct answer: Disruption of airflow through the compressor causing pressure reversal
A compressor stall occurs when the angle of attack of compressor blades exceeds the critical angle, causing airflow disruption and potential pressure reversal.
Question 6: What type of oil is used in most turbine engines?
- SAE 30 mineral oil
- Ashless dispersant mineral oil
- Synthetic ester-based oil (Correct answer)
- Automotive multi-viscosity oil
Correct answer: Synthetic ester-based oil
Turbine engines require synthetic ester-based oils that withstand the extreme temperatures and provide adequate lubrication at high altitudes.
Question 7: When is it permissible to use automotive gasoline (MOGAS) in an aircraft engine?
- Never under any circumstances
- Only when approved by an STC for that specific aircraft/engine combination (Correct answer)
- Whenever avgas is unavailable
- Only in engines below 100 horsepower
Correct answer: Only when approved by an STC for that specific aircraft/engine combination
MOGAS may only be used when an FAA-approved Supplemental Type Certificate (STC) authorizes its use for that specific aircraft and engine combination.
Airframe Mechanic Certification Powerplant Systems & Maintenance 3
An aircraft reciprocating engine is running rough.
You find one magneto drops 175 RPM during the mag check.
This most likely indicates: