The APU starter motor duty cycle is limited to not more than how many starts per hour with what delay between cranking attempts?

• A. 3 starts per 1 hour with a 2 minute delay
• B. 2 starts per 1 hour with a 5 minute delay
• C. 4 starts per 2 hours with a 3 minute delay
• D. 1 start per hour with a 10 minute delay

Answer: (A)

The key idea is that the APU starter motor has a thermal and electrical duty-cycle limit: you can crank it only a limited number of times in a short period, and you must allow a brief cooldown between attempts. This protects the starter windings and drive circuitry from overheating and excessive wear.

The best choice aligns with that rule: you’re allowed up to three starts within an hour, with a short pause—two minutes—between each cranking attempt. This cadence gives the starter enough rest to cool while still providing the needed chances to start the APU when quick readiness is important. Exceeding this limit risks overheating and potential starter failure, while a pattern with fewer starts or a longer delay would be unnecessarily restrictive for typical operations.