FAA Aviation Mechanic Powerplant (AMP)Turbine EnginesHard
On a turbine engine, the accessory gearbox provides mounting pads for components such as the fuel pump, oil pump, and generator. Which component transmits rotational power from the engine's main shaft to drive the accessory gearbox?
- AA radial driveshaft (tower shaft) geared to the compressor or turbine shaft
- BBleed air routed through a pneumatic turbine motor
- CThe propeller shaft directly, through a splined coupling
- DThe starter motor, which remains engaged throughout engine operation
Show answer & explanationAnswer & explanation
Correct answer: A. A radial driveshaft (tower shaft) geared to the compressor or turbine shaft
A radial (tower) driveshaft, geared into the main engine rotor shaft (typically the high-pressure/N2 shaft), transmits power outward to the accessory gearbox, which drives components such as fuel pumps, oil pumps, hydraulic pumps, and the generator/alternator.
Why the other options are wrong
- B. Bleed air pneumatic motors are used for starting some engines but do not continuously drive the accessory gearbox.
- C. The propeller shaft is a separate output on turboprops, unrelated to gearbox drive.
- D. The starter motor disengages after start and does not remain engaged to drive accessories.
Accessory Gearbox Drive
A radial (tower) driveshaft geared to the engine's main rotor shaft transmits power to the accessory gearbox, which drives fuel pumps, oil pumps, and generators.
- Tower shaft connects main shaft to accessory gearbox
- Gearbox mounts fuel pump, oil pump, generator, hydraulic pump
- Located typically at the bottom of the engine for accessibility
Memory trick: Tower shaft = the 'power line' running down from the main shaft to the accessory 'power strip.'