APU motor duty limits specify a maximum of how many start/attempts per hour, with what minimum delay between each?

• A. 3 start attempts per hour; 2 minutes delay between each
• B. 2 start attempts per hour; 3 minutes delay between each
• C. 4 start attempts per hour; 1 minute delay between each
• D. 5 start attempts per hour; 4 minutes delay between each

Answer: (A)

APU start limits exist to protect the starter and the unit from heat and mechanical stress during startup. Each start draws substantial current and torque, and the hardware needs a chance to cool and reset between attempts. Limiting to three start attempts per hour plus a minimum two-minute delay between starts prevents overheating, reduces wear on the starter motor, and allows proper self-checks by the system before the next attempt. In practice, you may try up to three starts in an hour, but you must wait at least two minutes between each attempt; after reaching three attempts, you’d wait until the next hour to try again. The other options would either push starts too densely or loosen the cooldown requirement, increasing the risk of damage or unreliable starts.