What are the APU Starter Limits?

• A. Three attempts in a one hour period, with a two minute waiting period between each attempt
• B. Two attempts in a 30-minute period, with a five minute waiting period between attempts
• C. Five attempts in two hours with no waiting
• D. One attempt per flight

Answer: (A)

The main idea here is that APU starts are limited to protect the starter and the APU from wear and overheating. There is a defined window in which you can attempt to start the APU, and you must observe a minimum time between attempts. This helps ensure the starter motor has a brief cooldown and the system isn’t stressed by rapid successive starts.

The best rule is that you may perform up to three start attempts within any 60-minute period, with at least a two-minute interval between each attempt. This means you can try up to three times in an hour, but you must wait at least two minutes after each attempt before trying again. If the APU doesn’t start after those attempts, you shouldn’t keep trying without following maintenance or approved procedures, because continuing could damage the starter or related systems.

Other options would either exceed the allowed number of attempts in the time window, omit the required cooling interval, or misstate how often you’re permitted to attempt starts, which would not align with standard APU protection practices.