The Aircraft Electrical System
How a light aircraft generates, stores and distributes electrical power — and what to do when it fails.
Most light aircraft use a simple direct-current electrical system built around an alternator, a battery and a bus that distributes power to the radios, lights, instruments and gear.
The components
- Alternator (or generator) — engine-driven; supplies electrical power in flight and recharges the battery. Needs the battery's field current to start producing.
- Battery — starts the engine and provides backup power; also smooths the system.
- Master switch — usually a split switch controlling the battery and alternator sides.
- Bus bar — distributes power to circuits, each protected by a circuit breaker or fuse.
- Ammeter / loadmeter — shows whether the battery is charging or discharging, or the alternator's load.
When it fails
An alternator failure (often shown by a discharging ammeter or a low-voltage light) means you're now running on battery alone — a limited reserve. Reduce the electrical load (non-essential lights, second radio), follow the POH (which may have you reset the alternator field), and land before the battery is exhausted. Note that the engine in most piston aircraft keeps running on its magnetos, which are independent of the electrical system — so an electrical failure is not an engine failure.
Common pitfalls
- Ignoring a discharging ammeter until radios and instruments quit.
- Forgetting which systems are electric (flaps, gear, some fuel pumps) versus independent.
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*Reference and training only — not for navigation. Always consult the current AIM, FAR/AIM, your aircraft’s POH/AFM and a certificated flight instructor.*