Engines Auxiliary Power Unit (APU) Practice Exam 2026 - Free APU Practice Questions and Study Guide

The APU is considered ready to supply electrical power when its generator is connected to the electrical bus and actively delivering power. The APU GEN OFF BUS light serves as the direct cue for that status: when this light is illuminated, it indicates the APU generator is in the position to feed power to the bus, confirming electrical readiness.

Starting the APU (switch ON) merely initiates the APU; it doesn’t by itself confirm that the generator is supplying power to the bus. EEC standby relates to engine control electronics, not the APU electrical output. An open APU door points to a physical access condition, not to whether electrical power is being provided.