FAA Powerplant Written Practice Test

When does the drive coupling of a turbine engine air starter stop turning?

1. During engine acceleration

2. At engine start-up

3. When the engine is shut down

4. During maintenance checks

The correct answer is: When the engine is shut down

The drive coupling of a turbine engine air starter stops turning when the engine is shut down because the starter has fulfilled its purpose of initiating engine operation. During engine start-up, the starter engages and drives the engine, facilitating acceleration until the engine achieves self-sustaining operation. Once the engine reaches its operational speed and parameters, the air starter disengages, but still continues to turn during the engine's running state. During maintenance checks, the starter is typically not engaged unless specific tests require it, and thus would not be actively turning in a normal check scenario. Therefore, the only time the drive coupling disconnects from the starter to the engine, ceasing all movement, is when the engine itself has been shut down, cutting off the airflow and pressure necessary for the starter to function.