FAA Aviation Mechanic General (AMG)Ground Operations and ServicingHard
During a turbine engine start attempt, the engine fails to reach a self-sustaining RPM and fuel is shut off, resulting in a hung/aborted start. Before attempting another start, the mechanic performs a dry motoring run using the starter with fuel and ignition OFF. What is the purpose of this step?
- ATo warm the engine oil for faster subsequent starts
- BTo check the starter generator's charging output under load
- CTo purge unburned fuel and vapors from the combustion section and prevent a tailpipe fire on restart
- DTo verify the fuel control unit's metering accuracy before the next attempt
Show answer & explanationAnswer & explanation
Correct answer: C. To purge unburned fuel and vapors from the combustion section and prevent a tailpipe fire on restart
A dry motoring run rotates the engine with the starter while fuel and ignition remain off, allowing airflow to clear any residual unburned fuel or vapor from the combustion chamber and tailpipe, preventing a fire or explosion when the next start attempt introduces ignition.
Why the other options are wrong
- A. Oil warming is not the intended function of a dry motoring run.
- B. Generator output checks are unrelated to the purpose of a dry motoring run.
- D. Fuel control accuracy is checked separately, not verified by a dry motoring run.
Dry Motoring Run
A procedure using only the starter (no fuel or ignition) to rotate a turbine engine and purge residual fuel after an aborted/hung start.
- Fuel and ignition are OFF during the run
- Clears unburned fuel/vapor from combustion section
- Prevents tailpipe fire on next start attempt
Memory trick: Dry motoring = 'dry cleaning' the engine before trying again.