FAA Powerplant Written Practice Test

How are accessories such as electric generators and hydraulic pumps powered on turbine-powered aircraft?

1. Driven directly by the engine

2. Driven at reduced speed from the high pressure compressor via a reduction gear box

3. Powered by batteries

4. Driven by the low pressure compressor

The correct answer is: Driven at reduced speed from the high pressure compressor via a reduction gear box

Electric generators and hydraulic pumps in turbine-powered aircraft are typically driven at reduced speed from the high-pressure compressor via a reduction gearbox. This approach allows the accessories to operate efficiently and at the appropriate speeds without subjecting them to the high rotational speeds of the engine itself. In turbine engines, the high-pressure compressor operates at a much higher speed than is suitable for most accessories, which is why the use of a reduction gearbox is essential. The gearbox reduces the speed of the rotating components to match the requirements of the accessories, ensuring both the reliability of the power supply and the longevity of the components involved. The direct drive from the engine or power from batteries is not a common method for powering these accessories in turbine aircraft. The low-pressure compressor does not provide the necessary conditions for driving the electrical generators and hydraulic pumps effectively. This makes the reduced-speed drive from the high-pressure compressor the preferred system in modern turbine engines.