FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsHard
During a normal turbine engine start sequence, at what point should the starter typically be disengaged?
- AWhen oil pressure reaches its maximum indicated value
- BWhen the exhaust gas temperature momentarily peaks during light-off
- CImmediately after fuel is introduced into the combustor
- DAt the manufacturer-specified self-sustaining speed, when the engine can accelerate to idle without starter assistance
Show answer & explanationAnswer & explanation
Correct answer: D. At the manufacturer-specified self-sustaining speed, when the engine can accelerate to idle without starter assistance
The starter's job is to accelerate the compressor to a speed at which the engine produces enough of its own gas generator energy to continue accelerating unassisted—the self-sustaining speed. Disengaging too early causes a hung start; disengaging normally occurs automatically or manually at this specified RPM to prevent overspeeding or damaging the starter.
Why the other options are wrong
- A. Oil pressure stabilization is unrelated to starter cutout timing.
- B. EGT peaking briefly during light-off is normal and not the disengagement criterion.
- C. Fuel introduction occurs earlier in the sequence, well before starter cutout.
Turbine Starter Cutout Speed
The self-sustaining speed is the RPM at which a turbine engine can continue accelerating to idle without starter assistance, at which point the starter is disengaged.
- Occurs after light-off, before idle RPM is reached
- Starter cutout may be automatic or manual
- Premature cutout can cause a hung start
- Extended starter engagement risks starter overheating/damage
Memory trick: Self-sustaining = the engine 'leaves the nest' on its own power.