FAA Powerplant Written Practice Test

What system disconnects power when sufficient engine speed is achieved?

1. The ignition system

2. The electrical matrix

3. The undercurrent relay

4. The fuel injection system

The correct answer is: The undercurrent relay

The correct choice refers to a mechanism commonly found in aircraft engine management systems, which ensures safe operation during the start phase of engine operations. The undercurrent relay is specifically designed to monitor electrical current and ensure that if an engine has not reached a predetermined speed, it will interrupt the circuit to prevent potential starts under unsafe conditions. This relay functions as a protective measure, allowing the ignition and fuel systems to operate only when sufficient engine speed, indicating that the engine is functioning correctly, has been achieved. In contrast, the ignition system is responsible for initiating combustion but does not manage the power disconnection based on engine speed. The electrical matrix typically refers to the broader context of electrical distribution systems and does not specifically monitor engine performance. The fuel injection system manages the delivery of fuel to the engine but does not handle power disconnection based on engine speed, focusing instead on optimal fuel-air mixtures for combustion at varying speeds.