What is the maximum speed for starting the APU?

The maximum speed for starting the Auxiliary Power Unit (APU) is correctly identified as 285 knots. This limit is crucial for ensuring that the APU operates safely and effectively. Starting the APU within the specified speed confines ensures that the unit does not experience undue stress or mechanical failure that could result from exceeding optimal conditions.

When operating an aircraft, exceeding the maximum speed during APU start-up can lead to challenges such as insufficient airflow for proper ignition or potential vibrations that could affect the integrity of the system. This speed limit is set based on operational parameters determined during testing and reflects the balance between performance and safety. Understanding this threshold is vital for all personnel involved in aircraft operation and maintenance to ensure the longevity and reliability of the APU system.