FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsMedium
A direct-cranking electric starter is engaged to start a reciprocating engine, and the engine successfully starts and runs. What component prevents the starter motor and its gear train from being driven and damaged by the now-running engine?
- AThe overrunning clutch (starter adapter)
- BThe Bendix drive spring
- CThe starter brush assembly
- DThe starter solenoid
Show answer & explanationAnswer & explanation
Correct answer: A. The overrunning clutch (starter adapter)
The overrunning clutch, part of the starter adapter, allows the starter to drive the engine during cranking but automatically disengages (freewheels) once the engine speed exceeds starter speed, preventing the running engine from over-speeding and damaging the starter. The solenoid only controls electrical power to the starter motor and does not provide mechanical disengagement, and the brush assembly conducts current to the armature.
Why the other options are wrong
- B. A Bendix drive spring is found on some automotive starters, not typical certificated aircraft starter adapters.
- C. Brushes carry current to the rotating armature; they don't protect against overspeed.
- D. The solenoid switches electrical current to the starter, not mechanical disengagement.
Overrunning Clutch (Starter Adapter)
A mechanical device in the starter drive train that engages to crank the engine but automatically freewheels once the engine exceeds starter speed, protecting the starter from damage.
- Prevents engine from over-driving the starter after start
- Allows one-way torque transfer only
- Located in the starter adapter/gear reduction housing
- Failure can cause starter to remain engaged and be destroyed
Memory trick: Clutch lets go once the engine outruns it