, ASA POWERPLANT ORALS FINAL EXAM 2025
ACTUAL EXAM 2 VERSIONS (VERSION A AND B)
COMPLETE QUESTIONS WITH DETAILED VERIFIED
ANSWERS (100% CORRECT ANSWERS) /ALREADY
GRADED A+
POWERPLANT ORALS – SAMPLE STUDY GUIDE (100 Q&As)
Section A: Engine Fundamentals, Construction, & Inspection (Q1-25)
1. Q: What are the four strokes of a reciprocating engine cycle?
A: Intake, Compression, Power, Exhaust.
2. Q: What is the purpose of the valves in a reciprocating engine?
A: To control the admission of the fuel/air mixture and the expulsion of exhaust gases at the
correct time in the cycle.
3. Q: What is valve overlap?
A: The period when both the intake and exhaust valves are open at the same time near the end
of the exhaust stroke, which helps scavenge exhaust and cool the cylinder.
4. Q: What does the bore of an engine cylinder refer to?
A: The inside diameter of the cylinder.
5. Q: What is engine compression ratio? Give an example.
A: The ratio of the volume of the cylinder with the piston at BDC to the volume at TDC.
Example: 8:1.
6. Q: What is the function of the crankshaft?
A: To convert the reciprocating (back-and-forth) motion of the pistons into rotary motion to
drive the propeller and engine accessories.
7. Q: What are the two main types of piston rings and their functions?
A: Compression rings (seal combustion gases, transfer heat) and Oil control rings (regulate oil
film on cylinder wall).
8. Q: What is a "hydraulic lifter" and its advantage?
A: A tappet that uses engine oil under pressure to automatically maintain zero valve clearance
(lash), reducing noise and maintenance.
,9. Q: How do you identify a cold cylinder during a power check?
A: By using a manifold pressure gauge to perform a "cylinder drop test." The cylinder with the
least RPM drop when its ignition is grounded is the weak ("cold") cylinder.
10. Q: What are the possible causes of a cold cylinder?
A: Ignition problems (bad plug, lead, mag), improper valve clearance, low compression, or
induction leak at that cylinder.
11. Q: What tools are used to check cylinder barrel out-of-round and taper?
A: A dial indicator or an inside micrometer.
12. Q: What is the purpose of dynamic dampers on a crankshaft?
A: To reduce torsional vibration (twisting) caused by power impulses.
13. Q: What is the difference between a "full-floating" and a "semi-floating" piston pin?
A: Full-floating: pin is free to rotate in both the piston bosses and connecting rod. It is retained
by lock rings. Semi-floating: pin is either pressed into the rod or piston bosses and is stationary
in one.
14. Q: During a compression check, what is indicated by a low, but building-up reading?
A: Likely poor (worn) piston rings. The pressure builds slowly as air leaks past the rings and fills
the crankcase.
15. Q: During a compression check, what is indicated by a low and immediate reading?
A: A "blow-by" indication, suggesting a major leak like a stuck or broken valve, hole in piston, or
failed head gasket.
16. Q: How is a hydraulic lifter inspected for proper operation after assembly?
A: It should be "leak-down" tested. A properly assembled lifter should not collapse under
moderate thumb pressure but should slowly collapse under a bench press.
17. Q: What is the primary purpose of the oil control ring?
A: To scrape excess oil off the cylinder wall on the piston's downstroke, returning it to the
crankcase, and leave a thin film for lubrication.
18. Q: What causes engine "detonation"?
A: Uncontrolled, explosive combustion of the fuel/air mixture after normal ignition, often due to
low fuel grade, high power with lean mixture, high CHT, or excessive deposits.
19. Q: What is "pre-ignition"?
A: Ignition of the fuel/air charge before the normal spark occurs, caused by a hot spot in the
cylinder (carbon, sharp edge, glowing plug).
, 20. Q: What is the purpose of a "starter-generator"?
A: It acts as an electric motor to crank the engine for starting, and then, once the engine is
running, it functions as a generator to produce electrical power.
21. Q: How are Lycoming and Continental crankshafts generally different in construction?
A: Lycoming often uses a one-piece forged crankshaft. Continental often uses a multi-piece
(split-case) forged crankshaft assembled with bolts.
22. Q: What is a "fuel injection" nozzle (discharge nozzle) and where is it located?
A: It is the component that meters and atomizes fuel directly into the cylinder intake port. It is
located in the cylinder head.
23. Q: What is a "FADEC" system?
A: Full Authority Digital Engine Control. A computerized system that controls both ignition and
fuel metering for optimal performance and efficiency, with no manual mixture control.
24. Q: What are the basic sections of a turbine engine?
A: Inlet, Compressor, Combustion, Turbine, Exhaust.
25. Q: What is the purpose of the turbine section?
A: To extract energy from the hot, high-velocity gases to drive the compressor (via the N1/N2
shaft) and the engine accessories. In a turboprop/turboshaft, it also drives the propeller/rotor.
Section B: Engine Lubrication & Cooling (Q26-40)
26. Q: What are the main functions of engine oil?
A: Lubrication, Cooling, Sealing, Cleaning, Corrosion Protection.
27. Q: What does the oil viscosity number (e.g., 20W-50) mean?
A: The first number (20W) indicates low-temperature (Winter) flow capability. The second
number (50) indicates high-temperature viscosity. It is a multi-grade oil.
28. Q: What type of oil is most commonly used in modern aviation piston engines?
A: Ashless Dispersant (AD) oil.
29. Q: What is the purpose of the oil bypass valve (pressure relief valve)?
A: To limit maximum oil system pressure by allowing oil to bypass the oil cooler/filter and return
to the sump if pressure is too high (e.g., cold start).
30. Q: What would cause a sudden drop in oil pressure?
A: Loss of oil quantity, pump failure, broken pressure line, or a serious internal failure (e.g.,
bearing failure).
ACTUAL EXAM 2 VERSIONS (VERSION A AND B)
COMPLETE QUESTIONS WITH DETAILED VERIFIED
ANSWERS (100% CORRECT ANSWERS) /ALREADY
GRADED A+
POWERPLANT ORALS – SAMPLE STUDY GUIDE (100 Q&As)
Section A: Engine Fundamentals, Construction, & Inspection (Q1-25)
1. Q: What are the four strokes of a reciprocating engine cycle?
A: Intake, Compression, Power, Exhaust.
2. Q: What is the purpose of the valves in a reciprocating engine?
A: To control the admission of the fuel/air mixture and the expulsion of exhaust gases at the
correct time in the cycle.
3. Q: What is valve overlap?
A: The period when both the intake and exhaust valves are open at the same time near the end
of the exhaust stroke, which helps scavenge exhaust and cool the cylinder.
4. Q: What does the bore of an engine cylinder refer to?
A: The inside diameter of the cylinder.
5. Q: What is engine compression ratio? Give an example.
A: The ratio of the volume of the cylinder with the piston at BDC to the volume at TDC.
Example: 8:1.
6. Q: What is the function of the crankshaft?
A: To convert the reciprocating (back-and-forth) motion of the pistons into rotary motion to
drive the propeller and engine accessories.
7. Q: What are the two main types of piston rings and their functions?
A: Compression rings (seal combustion gases, transfer heat) and Oil control rings (regulate oil
film on cylinder wall).
8. Q: What is a "hydraulic lifter" and its advantage?
A: A tappet that uses engine oil under pressure to automatically maintain zero valve clearance
(lash), reducing noise and maintenance.
,9. Q: How do you identify a cold cylinder during a power check?
A: By using a manifold pressure gauge to perform a "cylinder drop test." The cylinder with the
least RPM drop when its ignition is grounded is the weak ("cold") cylinder.
10. Q: What are the possible causes of a cold cylinder?
A: Ignition problems (bad plug, lead, mag), improper valve clearance, low compression, or
induction leak at that cylinder.
11. Q: What tools are used to check cylinder barrel out-of-round and taper?
A: A dial indicator or an inside micrometer.
12. Q: What is the purpose of dynamic dampers on a crankshaft?
A: To reduce torsional vibration (twisting) caused by power impulses.
13. Q: What is the difference between a "full-floating" and a "semi-floating" piston pin?
A: Full-floating: pin is free to rotate in both the piston bosses and connecting rod. It is retained
by lock rings. Semi-floating: pin is either pressed into the rod or piston bosses and is stationary
in one.
14. Q: During a compression check, what is indicated by a low, but building-up reading?
A: Likely poor (worn) piston rings. The pressure builds slowly as air leaks past the rings and fills
the crankcase.
15. Q: During a compression check, what is indicated by a low and immediate reading?
A: A "blow-by" indication, suggesting a major leak like a stuck or broken valve, hole in piston, or
failed head gasket.
16. Q: How is a hydraulic lifter inspected for proper operation after assembly?
A: It should be "leak-down" tested. A properly assembled lifter should not collapse under
moderate thumb pressure but should slowly collapse under a bench press.
17. Q: What is the primary purpose of the oil control ring?
A: To scrape excess oil off the cylinder wall on the piston's downstroke, returning it to the
crankcase, and leave a thin film for lubrication.
18. Q: What causes engine "detonation"?
A: Uncontrolled, explosive combustion of the fuel/air mixture after normal ignition, often due to
low fuel grade, high power with lean mixture, high CHT, or excessive deposits.
19. Q: What is "pre-ignition"?
A: Ignition of the fuel/air charge before the normal spark occurs, caused by a hot spot in the
cylinder (carbon, sharp edge, glowing plug).
, 20. Q: What is the purpose of a "starter-generator"?
A: It acts as an electric motor to crank the engine for starting, and then, once the engine is
running, it functions as a generator to produce electrical power.
21. Q: How are Lycoming and Continental crankshafts generally different in construction?
A: Lycoming often uses a one-piece forged crankshaft. Continental often uses a multi-piece
(split-case) forged crankshaft assembled with bolts.
22. Q: What is a "fuel injection" nozzle (discharge nozzle) and where is it located?
A: It is the component that meters and atomizes fuel directly into the cylinder intake port. It is
located in the cylinder head.
23. Q: What is a "FADEC" system?
A: Full Authority Digital Engine Control. A computerized system that controls both ignition and
fuel metering for optimal performance and efficiency, with no manual mixture control.
24. Q: What are the basic sections of a turbine engine?
A: Inlet, Compressor, Combustion, Turbine, Exhaust.
25. Q: What is the purpose of the turbine section?
A: To extract energy from the hot, high-velocity gases to drive the compressor (via the N1/N2
shaft) and the engine accessories. In a turboprop/turboshaft, it also drives the propeller/rotor.
Section B: Engine Lubrication & Cooling (Q26-40)
26. Q: What are the main functions of engine oil?
A: Lubrication, Cooling, Sealing, Cleaning, Corrosion Protection.
27. Q: What does the oil viscosity number (e.g., 20W-50) mean?
A: The first number (20W) indicates low-temperature (Winter) flow capability. The second
number (50) indicates high-temperature viscosity. It is a multi-grade oil.
28. Q: What type of oil is most commonly used in modern aviation piston engines?
A: Ashless Dispersant (AD) oil.
29. Q: What is the purpose of the oil bypass valve (pressure relief valve)?
A: To limit maximum oil system pressure by allowing oil to bypass the oil cooler/filter and return
to the sump if pressure is too high (e.g., cold start).
30. Q: What would cause a sudden drop in oil pressure?
A: Loss of oil quantity, pump failure, broken pressure line, or a serious internal failure (e.g.,
bearing failure).
