AMT Powerplant Systems & Engine Maintenance 3 — Questions and Answers
Question 1: An engine-driven fuel pump has a relief valve. What is the purpose of this valve?
- To prevent fuel from flowing backward when the engine is shut down
- To bypass excess fuel back to the inlet when outlet pressure exceeds the set value (Correct answer)
- To provide an alternate fuel path if the primary filter clogs
- To regulate the mixture ratio at high altitude
Correct answer: To bypass excess fuel back to the inlet when outlet pressure exceeds the set value
The relief valve in an engine-driven fuel pump bypasses excess fuel back to the pump inlet to maintain a constant, regulated outlet pressure.
Question 2: What condition is indicated when a turbine engine's exhaust gas temperature (EGT) is higher than normal at a given power setting?
- The engine is operating more efficiently than normal
- Possible turbine damage, compressor fouling, or deterioration reducing engine efficiency (Correct answer)
- Excess air is entering the combustion chamber
- Fuel flow is lower than normal for that power setting
Correct answer: Possible turbine damage, compressor fouling, or deterioration reducing engine efficiency
High EGT at a given power setting suggests reduced engine efficiency from causes such as compressor fouling, turbine damage, or bleed air leaks, requiring investigation.
Question 3: Detonation in a reciprocating engine is best defined as:
- Premature ignition of the fuel-air charge before the spark fires
- Explosive, uncontrolled burning of the fuel-air mixture after normal ignition (Correct answer)
- Fuel vaporizing inside the fuel lines before reaching the carburetor
- Ignition of residual fuel in the exhaust manifold
Correct answer: Explosive, uncontrolled burning of the fuel-air mixture after normal ignition
Detonation is the sudden, explosive auto-ignition of the end gas in the cylinder after normal spark ignition, producing damaging pressure spikes.
Question 4: When performing a magnetic particle inspection on engine steel components, what type of defects can this method detect?
- Subsurface voids deeper than 1 inch
- Surface and near-surface discontinuities in ferromagnetic materials (Correct answer)
- Corrosion inside aluminum alloy castings
- Disbonding in composite fan blades
Correct answer: Surface and near-surface discontinuities in ferromagnetic materials
Magnetic particle inspection reveals surface and near-surface cracks or discontinuities in ferromagnetic (iron/steel) components by attracting iron particles to flux leakage points.
Question 5: What is the function of the pressurization and dump valve in a gas turbine fuel system?
- Regulates high-pressure fuel to the fuel control unit during starting
- Prevents secondary fuel nozzles from opening until primary fuel pressure is sufficient, and dumps manifold fuel on shutdown (Correct answer)
- Provides a bypass path around the fuel heater during cold starts
- Measures fuel flow to provide data to the engine fuel control
Correct answer: Prevents secondary fuel nozzles from opening until primary fuel pressure is sufficient, and dumps manifold fuel on shutdown
The pressurizing and dump valve holds back fuel from secondary nozzles until pressure is adequate for proper atomization, then drains the fuel manifold when the engine shuts down to prevent coking.
Question 6: Which type of oil system is used on most gas turbine engines to ensure continuous lubrication during unusual flight attitudes?
- Wet-sump gravity-feed system
- Dry-sump pressure-feed system with a dedicated oil tank (Correct answer)
- Semi-dry sump with a standpipe reserve
- Open-circuit total-loss lubrication system
Correct answer: Dry-sump pressure-feed system with a dedicated oil tank
Gas turbine engines use a dry-sump system with a dedicated tank and pressure-fed lubrication so oil supply is not affected by aircraft attitude changes.
Question 7: What is 'compressor surge' in a turbine engine?
- A sudden increase in compressor RPM above the redline limit
- A disruption of airflow through the compressor causing rapid, repetitive flow reversal and loud banging (Correct answer)
- Normal compressor bleed valve operation during deceleration
- Vibration caused by foreign object damage to compressor blades
Correct answer: A disruption of airflow through the compressor causing rapid, repetitive flow reversal and loud banging
Compressor surge is an aerodynamic instability in which airflow through the compressor reverses rapidly, causing loud bangs, power loss, and potential damage.
AMT Powerplant Systems & Engine Maintenance 3
An engine-driven fuel pump has a relief valve.
What is the purpose of this valve?