FAA Powerplant Written Practice Test

In automatic starting systems on small reciprocating engine aircraft, what happens to allow current to flow to the starter motor?

1. A capacitor is energized

2. A starter solenoid is energized

3. A relay is activated

4. A circuit breaker is reset

The correct answer is: A starter solenoid is energized

In automatic starting systems used in small reciprocating engine aircraft, the flow of current to the starter motor is facilitated by energizing a starter solenoid. The starter solenoid acts as a switch that, when activated, completes the electrical circuit between the battery and the starter motor. This activation typically occurs when a start signal is received from the ignition or a motion sensor that detects the need to start the engine. The solenoid's role is critical because it not only closes the circuit to allow high current to flow to the starter motor, which is necessary to crank the engine, but it also helps to isolate the starter circuit from the battery during normal operation. This prevents any unintended current draw when the engine is not starting. Understanding the working of the starter solenoid is essential, as it differs from other components like capacitors, relays, or circuit breakers, which serve different functions in the electrical system. For instance, a capacitor stores electrical energy, a relay switches circuits without handling the heavy current directly, and a circuit breaker protects the circuit from overloads by interrupting current flow.