During a turbine engine start, the engine successfully lights off but the RPM stagnates at a value well below normal idle speed and fails to continue accelerating. Which of the following is the most likely cause of this condition?
- AThe overrunning clutch disengaged prematurely at idle RPM
- BThe fuel control unit scheduled too little fuel during the initial light-off phase only
- CThe igniters remained energized after light-off
- DInsufficient starter torque or inadequate air supply pressure to fully accelerate the engine to self-sustaining speed
Show answer & explanationAnswer & explanation
Correct answer: D. Insufficient starter torque or inadequate air supply pressure to fully accelerate the engine to self-sustaining speed
A 'hung start' occurs when the engine lights but does not have enough combined starter torque and airflow energy to accelerate past a stagnation point to self-sustaining idle RPM, often due to low starter air pressure/voltage or a weak starter. Igniters remaining on does not cause stagnation, insufficient fuel only at light-off would more likely cause a no-light or delayed light rather than stagnation after light-off, and clutch disengagement at idle would be a separate, later mechanical event unrelated to acceleration stagnation during the start sequence.
Why the other options are wrong
- A. The overrunning clutch disengages appropriately once the engine exceeds starter speed; premature disengagement at low RPM is not the typical hung start cause.
- B. Reduced initial fuel would more likely delay or prevent light-off rather than cause stagnation after ignition.
- C. Continuous ignition does not limit RPM acceleration; it's often intentional for reliable combustion.
Turbine Engine Hung Start
A start malfunction where the engine ignites but fails to accelerate past a certain RPM due to insufficient starter torque or airflow, requiring an aborted start.
- Engine lights off but RPM plateaus below idle
- Usually caused by low starter air pressure or weak electrical starter power
- Must be aborted per checklist to prevent overheating
- Distinct from hot start (temperature) and no-light start (no ignition)
Memory trick: Not enough push to climb the hill to idle