FAA Powerplant Written Practice Test

What is the primary purpose of a return spring in a direct cranking reciprocating engine starter?

1. To engage the starter jaw

2. To retract the starter jaw

3. To provide electrical contact

4. To support the starter motor

The correct answer is: To retract the starter jaw

The primary purpose of a return spring in a direct cranking reciprocating engine starter is to retract the starter jaw. This component is crucial in the starting process, as the starter jaw must engage with the engine's flywheel in order to crank the engine. Once the engine is started, the return spring ensures that the starter jaw is disengaged from the flywheel promptly to prevent damage to the starter or the engine. When the engine fires and begins to operate, the momentum from the engine helps the starter jaw disengage, but the return spring provides the necessary force to ensure a swift and reliable retraction. This action minimizes the risk of continuous engagement that could lead to wear or failure of the starter mechanism or the flywheel. In contrast, the other choices pertain to functions that are not the primary role of the return spring. Engaging the starter jaw is the initial action when starting; providing electrical contact is primarily the function of the starter solenoid or the engagement mechanism itself; and supporting the starter motor relates to structural stability rather than the specific role of the return spring.