Free CAAS SAR-66 Module 14 Propulsion Practice Questions

Sample Practice Questions

Try these 10 sample questions from the CAAS SAR-66 Module 14 Propulsion practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1How are intake, compression, combustion and exhaust carried out during steady operation of a gas turbine engine?

   1. A.They occur simultaneously in separate engine sections.Correct answer: A
   2. B.They alternate in a single chamber over four strokes.
   3. C.They occur only during alternating shaft revolutions.
   4. D.They progress as isolated pulses through one section.

   Explanation: The FAA handbook states: "separate sections are devoted to each function, and all functions are performed simultaneously without interruption." Different sections perform the functions continuously. The other descriptions incorrectly apply intermittent or reciprocating-cycle operation.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Types & Construction

2. 2On a turbofan that uses EPR for power setting, what does the engine pressure ratio indication represent operationally?

   1. A.The thrust being developed by the engine.Correct answer: A
   2. B.The amount of oil remaining in the engine tank.
   3. C.The rate of rotation of the propeller shaft.
   4. D.The temperature difference across the fuel filter.

   Explanation: The FAA handbook states: "Engine pressure ratio (EPR) is an indication of the thrust being developed by a turbofan engine" EPR is a thrust-setting indication for the specified engines. Oil quantity, propeller rpm and fuel-filter temperature are different measurements.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Engine Pressure Ratio Indicator

3. 3Which rotating assembly must the starter turn to establish combustion-supporting airflow in a dual-spool gas turbine?

   1. A.The high-pressure compressor assembly.Correct answer: A
   2. B.Only the low-pressure fan assembly.
   3. C.Only the independent free power turbine.
   4. D.Only the propeller reduction-gear output shaft.

   Explanation: The FAA handbook states: "Gas turbine engines are started by rotating the high-pressure compressor." Rotating the core high-pressure compressor establishes combustion airflow; rotating only the fan or independent output assembly does not establish the required core rotation.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Gas Turbine Engine Starters

4. 4What is the compressor's primary function in a gas turbine engine?

   1. A.Lower the gas temperature before it enters the turbine.
   2. B.Supply the burners with air at the required pressure.Correct answer: B
   3. C.Convert exhaust-gas energy into useful shaft rotation.
   4. D.Accelerate burned gases through the exhaust nozzle.

   Explanation: The FAA handbook states: "the compressor must increase the pressure of the mass of air received from the air inlet duct, and then discharge it to the burners in the quantity and at the pressures required." The compressor delivers compressed combustion air. Cooling, turbine work extraction and exhaust acceleration describe other functions.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Compressor Section

5. 5Where are the total-pressure pickups used by the described EPR indication system?

   1. A.At the compressor inlet and compressor discharge.
   2. B.At the engine inlet and the turbine exhaust.Correct answer: B
   3. C.At the combustor inlet and the first turbine inlet.
   4. D.At the fan inlet and the bypass-nozzle outlet.

   Explanation: The FAA handbook states: "It is instrumented by total pressure pickups in the engine inlet (Pt2) and in the turbine exhaust (Pt7)." The described EPR system compares Pt2 with Pt7. The alternatives compare different stations, confusing EPR with compressor pressure ratio or other gas-path pressure relationships.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Engine Pressure Ratio Indicator

6. 6For the typical gas turbine starting sequence described by the FAA, which order establishes combustion?

   1. A.Admit fuel, stop the compressor, then energise ignition.
   2. B.Establish compressor airflow, turn on ignition, then introduce fuel.Correct answer: B
   3. C.Energise ignition, admit fuel, then wait before rotating the compressor.
   4. D.Admit fuel and ignition together before establishing any compressor airflow.

   Explanation: The FAA handbook states: "As soon as the starter has accelerated the compressor sufficiently to establish airflow through the engine, the ignition is turned on followed by the fuel." The order ensures adequate airflow before burning begins. The alternatives admit fuel too early or stop the airflow. The particular engine's approved procedure remains controlling.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Gas Turbine Engine Starters

7. 7From which part of a gas turbine engine is air normally extracted for a pneumatic engine-starting supply?

   1. A.The inlet duct ahead of the compressor.
   2. B.The core exhaust after the final turbine.
   3. C.The compressor at an appropriate pressure stage.Correct answer: C
   4. D.The fan bypass duct downstream of the fan.

   Explanation: The FAA handbook states: "The bleed-air is taken from any of the various pressure stages of the compressor." The inlet and bypass ducts do not provide the stated compressor-stage bleed source; the core exhaust is hot combustion gas rather than compressor bleed air.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Compressor Section

8. 8Why are gas turbine tachometers commonly graduated in percent rpm?

   1. A.To show the percentage of available shaft horsepower.
   2. B.To show the proportion of inlet air that bypasses the core.
   3. C.To provide a common speed-comparison basis across engine types.Correct answer: C
   4. D.To show the percentage of the commanded engine thrust.

   Explanation: The FAA handbook states: "Tachometers are usually calibrated in percent rpm so that various types of engines can be operated on the same basis of comparison." Percent rpm is a rotational-speed reference, distinct from torque-derived power percentage, bypass mass-flow ratio or commanded thrust percentage.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Tachometer

9. 9Why must starter assistance continue after initial light-off during a normal turbine start?

   1. A.Light-off proves full rated power, so the starter merely smooths the indication.
   2. B.The starter provides only electrical indication power after the first flame.
   3. C.The engine must still accelerate to a speed that supports its own operation.Correct answer: C
   4. D.The starter must carry the compressor load throughout normal engine operation.

   Explanation: The FAA handbook states: "the starter must continue to assist the engine until the engine reaches a self-sustaining speed." Initial combustion does not yet prove self-sustaining power. Starter torque assists acceleration until the engine can support its own operation; it is neither merely indication power nor a permanent compressor drive.

   Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Gas Turbine Engine Starters

10. 10Which combination constitutes a gas turbine engine spool?

    1. A.A combustor liner, fuel manifold and ignition unit.
    2. B.An inlet lip, bypass duct and exhaust nozzle assembly.
    3. C.A propeller, reduction gearbox and accessory housing.
    4. D.A compressor, its shaft and the turbines driving it.Correct answer: D

    Explanation: The FAA handbook states: "a spool is a compressor and a shaft and turbines that drive that compressor" A spool links its compressor and driving turbine through a shaft; the other groups mix stationary components or separate assemblies.

    Reference: FAA Aviation Maintenance Technician Handbook—Powerplant — Types & Construction