AMT Powerplant Systems & Engine Maintenance 2 — Questions and Answers
Question 1: What is the primary purpose of an aircraft engine's intercooler?
- To cool the engine oil before it enters the crankcase
- To cool the compressed induction air between the supercharger and the intake manifold (Correct answer)
- To reduce exhaust gas temperature before the muffler
- To lower fuel temperature in the fuel injection system
Correct answer: To cool the compressed induction air between the supercharger and the intake manifold
An intercooler cools supercharged or turbocharged induction air between the compressor and the intake manifold, increasing air density for better combustion.
Question 2: When inspecting a turbine engine for a hot-section inspection, which component is most susceptible to thermal fatigue cracking?
- Compressor inlet guide vanes
- Turbine blades and nozzle guide vanes (Correct answer)
- Accessory gearbox housing
- Combustor drain valves
Correct answer: Turbine blades and nozzle guide vanes
Turbine blades and nozzle guide vanes operate at the highest temperatures in the engine and are most susceptible to thermal fatigue cracking.
Question 3: A reciprocating engine is running rough and backfiring through the induction system. The most likely cause is:
- Over-rich mixture at cruise power
- Excessively lean mixture causing early ignition (Correct answer)
- High oil pressure restricting fuel flow
- Exhaust valve sticking open
Correct answer: Excessively lean mixture causing early ignition
An excessively lean mixture can cause slow or late combustion that continues into the induction cycle, causing backfiring through the intake.
Question 4: What does the term 'critical altitude' refer to in a turbocharged engine?
- The altitude at which the engine must be shut down due to temperature limits
- The highest altitude at which the turbocharger can maintain rated manifold pressure (Correct answer)
- The altitude at which fuel vaporization becomes problematic
- The density altitude above which the engine produces maximum power
Correct answer: The highest altitude at which the turbocharger can maintain rated manifold pressure
Critical altitude is the maximum altitude at which the turbocharger can maintain the rated manifold pressure; above this, manifold pressure begins to drop.
Question 5: During a compression check on a reciprocating engine, a low reading that improves significantly when oil is squirted into the cylinder indicates:
- Leaking intake or exhaust valves
- Worn or broken piston rings (Correct answer)
- A cracked cylinder head
- Burned exhaust valve
Correct answer: Worn or broken piston rings
Oil temporarily seals piston ring gaps, so a low reading that improves with oil injection points to worn or damaged piston rings as the source of leakage.
Question 6: Which fuel system component prevents vapor lock by maintaining positive pressure on the fuel at the engine-driven pump inlet?
- Fuel selector valve
- Boost pump (auxiliary electric fuel pump) (Correct answer)
- Fuel strainer
- Primer pump
Correct answer: Boost pump (auxiliary electric fuel pump)
The boost (auxiliary electric fuel) pump maintains positive pressure in the fuel line to the engine-driven pump, preventing vapor lock especially during hot starts and high-altitude operations.
Question 7: What is the result of operating a gas turbine engine at a turbine inlet temperature (TIT) exceeding the manufacturer's limits?
- Increased compressor stall margin
- Accelerated creep and oxidation of turbine blades leading to premature failure (Correct answer)
- Reduced specific fuel consumption improving efficiency
- Improved combustion stability across all power settings
Correct answer: Accelerated creep and oxidation of turbine blades leading to premature failure
Excessive TIT accelerates creep deformation and oxidation of turbine blades, drastically shortening their service life and risking catastrophic failure.
AMT Powerplant Systems & Engine Maintenance 2
What is the primary purpose of an aircraft engine's intercooler?