FAA Powerplant Written Practice Test

What is the primary benefit of using a reduction gear box in turbine aircraft?

1. Increase overall thrust

2. Enhance propulsive efficiency

3. Allow accessories to operate at reduced speeds

4. Lower operational costs

The correct answer is: Allow accessories to operate at reduced speeds

The primary benefit of using a reduction gear box in turbine aircraft is to allow accessories to operate at reduced speeds. In turbine engines, the high-speed rotation of the turbine might not be suitable for certain accessories—like generators, pumps, and other systems—that need to operate at optimal lower speeds. The reduction gearbox effectively translates high rotational speeds from the turbine to lower, more useful speeds for these accessories. This setup ensures that the accessories function efficiently without being exposed to the full high speeds which could lead to excessive wear or damage. It also helps in managing the power distribution within the engine, optimizing the overall performance of the aircraft systems while maintaining reliability and safety. Enhancing propulsive efficiency or increasing overall thrust are secondary benefits and depend on other design considerations. Lower operational costs may result indirectly from the efficient operation of accessories but is not the primary function of the reduction gear box.