Definition
The energy supply that drives an aircraft instrument or system. In light aircraft, the most common power sources are the engine-driven vacuum (or pressure) pump, the electrical system (battery and alternator/generator), and ram air or static air pressure from the pitot-static system. Different instruments rely on different power sources, which is why a single failure does not disable every instrument at once.
Plain English
Whatever supplies the energy that makes an instrument or system work — usually the engine, the electrical system, or air pressure from outside the aircraft.
Context Anchor
Used in instrument failure discussions when deciding whether one failed supply may affect more than one instrument or system.
Why Pilots Care
Loss of a power source can render critical attitude and heading information unusable, forcing transition to partial-panel techniques or backup instruments to maintain control.
Intuition Check
Do not assume “power source” means only the engine. In this context, it means the specific supply that makes an instrument or system work, such as electricity or suction.
Example Sentence 1
When the vacuum pump quit, the pilot lost the instruments that shared that power source — the attitude and heading indicators.
Example Sentence 2
After the vacuum pump failed, the attitude indicator was lost because its power source had been interrupted.