Successful APU starts are limited to

• A. 6 consecutive attempts at 10 minute intervals with a 1 hour rest
• B. 6 consecutive attempts at 5 minute intervals with a 2 hour rest
• C. 5 consecutive attempts at 10 minute intervals with a 1 hour rest
• D. 8 consecutive attempts at 10 minute intervals with a 1 hour rest

Answer: (A)

APU start limits are in place to protect the unit from overheating and excessive wear caused by repeated starts. The standard practice allows up to six start attempts in a sequence, with about ten minutes between each try to allow cooling and system checks. After completing those six attempts, a one-hour rest is required before attempting another start sequence. This balance helps ensure the APU remains reliable while giving it time to cool and recover.

So six consecutive attempts at ten-minute intervals with a one-hour rest matches this limit, making it the best option. Other configurations change either the number of attempts, the interval between attempts, or omit the required rest, which would violate the prescribed limits.