If the APU automatically shuts down due to overspeed, what steps should be taken?

If the APU automatically shuts down due to overspeed, what steps should be taken?

• A. Confirm shutdown, inspect for abnormal load or turbine damage, allow deceleration, and investigate root cause before reuse.
• B. Immediately restart to verify operation.
• C. Ignore and attempt to restart while running at maximum speed.
• D. Replace the APU without inspection.

Answer: (A)

When the APU shuts down automatically due to overspeed, the priority is to safely verify and understand what happened before trying to reuse the unit. Start by confirming that the shutdown actually occurred and that the APU rotor is decelerating to a safe speed. Then inspect for signs of abnormal load, turbine damage, or any fault indications that could have caused the overspeed. Allow the turbine to decelerate fully and stabilize, ensuring there’s no residual high speed or abnormal conditions. Finally, investigate and identify the root cause of the overspeed so you can address it before reusing the APU. Restarting immediately or attempting to run at maximum speed without this check risks repeating the overspeed and could cause further damage or a dangerous condition. Replacing the APU without inspection also misses potential damage or faults that need repair.

When the APU shuts down automatically due to overspeed, the priority is to safely verify and understand what happened before trying to reuse the unit. Start by confirming that the shutdown actually occurred and that the APU rotor is decelerating to a safe speed. Then inspect for signs of abnormal load, turbine damage, or any fault indications that could have caused the overspeed. Allow the turbine to decelerate fully and stabilize, ensuring there’s no residual high speed or abnormal conditions. Finally, investigate and identify the root cause of the overspeed so you can address it before reusing the APU. Restarting immediately or attempting to run at maximum speed without this check risks repeating the overspeed and could cause further damage or a dangerous condition. Replacing the APU without inspection also misses potential damage or faults that need repair.