Final answer:
The permissible number of APU starts on battery power before a waiting period is typically two to three starts, after which a 20-minute cooling period is recommended. This is to prevent overheating and protect the APU, with the exact number found in the aircraft's operating manuals. Compliance with these guidelines ensures the safety and efficiency of aircraft operations.
Step-by-step explanation:
The question pertains to the permissible number of Auxiliary Power Unit (APU) starts on battery power before a mandatory cooling period is required. Typically, an APU can be started a limited number of times (often two or three) in quick succession on battery power. After exceeding this limit, a cooling period of around 20 minutes is generally recommended to prevent overheating and potential damage to the APU or its starter system. This prevents excessive wear and potential failures, ensuring the longevity and reliability of the APU.
The exact number of attempts can be aircraft-specific and should be found in the aircraft's operating manuals or manufacturer's guidelines. It is important for pilots and ground crew to adhere to these guidelines for safe and efficient operations.
Note that this operational procedure is related to the concern of battery life span and performance, such as the case where a sample of 30 batteries showed only a 2% probability of having a life span of at most 16.7 hours.