Answers - Powerplant Fuel Metering Systems

1. b
Automatic fuel control units sense power lever position, engine rpm, compressor inlet air temperature and density, and burner pressure or discharge pressure. Since turbine engine aircraft do not utilize a mixture control, it is not a factor in the operation of the fuel control unit.

2. a
In order to stabilize internal components and ensure consistent results, most engine manufacturers specify that all trim adjustments be made in the increase direction. In other words, the engine will idle at a value just above the minimum idle speed and maximum thrust will be obtained slightly before the power levers reach the full forward position.

3. b
Field adjustments, or trimming adjustments made to turbine engine fuel controls are limited to idle rpm and maximum speed adjustments.

4. a
A supervisory electronic engine control (EEC) includes a computer that monitors several engine operating criteria and uses this information to adjust a standard hydromechanical fuel control unit (FCU) to obtain a constant thrust for a given power lever position.

5. b
A full-authority electronic engine control (EEC) performs all of the functions required to operate an engine. In other words, it receives data from the aircraft and engine systems and then issues commands to various actuators that control engine operating parameters.

6. c
Any fault in a supervisory electronic engine control (EEC) automatically causes the EEC to relinquish engine control to the hydromechanical control unit. At the same time, the EEC sends a signal to the cockpit that illuminates an annunciator light to inform the flight crew of the change in operating mode.

7. b
The active clearance control (ACC) portion of an electronic engine control (EEC) system controls turbine blade-to-engine case clearances by controlling the amount of air that is directed through the engine case. By keeping clearances to a minimum, pressure losses caused by air leakage at the blade tips is minimized.

8. a
Turbine engines are designed to operate using a specific type of fuel with a given BTU value and specific gravity. Therefore, if a performance check is made on an engine using an alternate fuel, the specific gravity setting should be checked and changed as necessary on the fuel control unit to ensure proper performance. Although an alternate fuel is likely to cause an engine to perform differently.

9. c
Part of the procedure used for trimming an engine includes measuring engine inlet barometric pressure and ambient temperature. To ensure a temperature value that is accurate, it is common practice to hang a thermometer in the shade of the nose wheel-well.

10. c
Facing an engine into a strong wind produces the same effect as improving the efficiency of the engine's compressor. Therefore, if an engine is trimmed while facing into an excessive wind, a false high compression and turbine discharge pressure, as well as a subsequent low trim are likely to occur.

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