Plain English Meaning

A separate power line in the airplane that feeds only the radios, navigation gear, and other electronic equipment, so they can be switched on or off as a group without affecting the rest of the airplane's electrical system.

Full Definition

A dedicated electrical distribution bar that supplies power exclusively to the aircraft's avionics equipment, such as radios, navigation receivers, transponders, and flight displays. It is normally isolated from the main electrical bus by an avionics master switch or relay, allowing the avionics to be powered down independently to protect them from voltage spikes during engine start and shutdown.