What should be done if the APU RPM exceeds the maximum rotor speed?

When the APU (Auxiliary Power Unit) RPM exceeds the maximum rotor speed, the safest and most effective course of action is to shut it down immediately. This is because exceeding the maximum rotor speed could lead to potential damage to the APU and increase the risk of failure, which can pose a safety hazard. Immediate shutdown helps to prevent further mechanical issues or catastrophic failure.

Shutting down the APU allows for controlled conditions to assess any damage that may have occurred and prevents the escalation of the problem. Taking this action also aligns with standard safety protocols, which prioritize minimizing risk to personnel and equipment.

While other options may seem prudent in certain contexts, they do not address the urgent nature of the condition as effectively. Reducing power might mitigate the situation temporarily but does not eliminate the risk associated with the overspeed condition. Ignoring the issue could lead to further complications and is not advisable as it undermines safety protocols. Reporting to maintenance is important for follow-up, but it should occur after the immediate danger has been addressed by shutting down the APU.