FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsEasy
A reciprocating engine is equipped with a direct-cranking electric starter controlled through a solenoid switch. What is the function of this solenoid?
- AIt automatically retards the magneto timing while the starter is engaged
- BIt reduces the starter motor's rotational speed during the initial engagement phase
- CIt converts the aircraft's DC battery power into AC for the starter motor
- DIt allows a low-current cockpit switch to remotely control the high-current circuit to the starter motor
Show answer & explanationAnswer & explanation
Correct answer: D. It allows a low-current cockpit switch to remotely control the high-current circuit to the starter motor
A starter solenoid is a heavy-duty relay. A small current from the cockpit starter switch energizes the solenoid coil, which closes heavy contacts that carry the large current needed to run the starter motor, keeping the cockpit wiring light and simple.
Why the other options are wrong
- A. Timing retard (if used) is a separate magneto mechanism, not part of the starter solenoid.
- B. Speed reduction is not the solenoid's job; that is handled by gearing/clutch mechanisms.
- C. Starters use DC directly; no AC conversion occurs.
Starter Solenoid/Relay
A remotely operated switch that uses a small control current to close heavy contacts, delivering high battery current to the starter motor.
- Reduces size/weight of cockpit wiring
- Energized by starter switch or starter button
- Contacts carry hundreds of amps to starter motor
- Common on both reciprocating and light turbine starters
Memory trick: Small switch, big solenoid muscle.