At what engine RPM does the ignition system in the APU automatically cut out?

The ignition system in the Auxiliary Power Unit (APU) is designed to operate within specific parameters for optimal performance and safety. The ignition cutout occurs at 95% engine RPM. This is crucial for a few reasons: it helps prevent potential damage to the ignition system and ensures a smooth transition of power as the APU reaches operating speeds.

At 95% RPM, the APU has sufficiently reached a stable operating condition where the ignition is no longer needed to maintain combustion. This automatic cutout feature is essential in improving the reliability of the APU by minimizing unnecessary wear on the ignition system and reducing the risk of electrical interference that could arise from prolonged ignition activity at high RPM.

Understanding this cutout function is vital for maintenance and operation, as it allows crew members to monitor APU performance effectively and ensures that systems are operating safely within manufacturer specifications.