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What Powers a Plane: Generators, Batteries and Backups

2 min read

The short answer

An airliner makes its own electricity from several separate sources — generators on each engine, a small extra engine in the tail, and batteries. If one source stops, another takes over automatically. Many airliners even carry a small propeller that can pop out to make emergency power.

A Power Station in the Sky

Everything on a modern plane runs on electricity: the screens in the cockpit, the radios, the computers, the lights and the galley. So airliners are designed with several separate power sources, each able to step in for another.

1. Generators on the Engines

Each engine drives at least one generator, just like a car engine charges its battery. On a twin-engine airliner, either engine's generators can power everything essential on their own.

2. A Small Engine in the Tail

At the very back of most airliners is a small extra engine called the APU (auxiliary power unit). It powers the plane at the gate, before the main engines start — that's the hum you hear while boarding. In flight, it can be started as an extra source of power if needed.

3. Batteries

Large batteries keep the most important instruments and radios running, even if every generator stopped. They also help start the APU.

4. The Hidden Propeller

Many airliners carry a small ram air turbine — a little propeller tucked inside the plane. If ever needed, it drops out into the airflow and spins like a wind turbine, making power for the essential systems. Most passengers will never see one in action.

Switching Is Automatic

The plane's systems are arranged so that if one source drops out, another takes its place — often without passengers noticing anything at all. Read about backup systems.

What You Might Notice

  • The lights flicker briefly when the plane switches from ground power or the APU to the engines. That's normal.
  • A hum from the tail at the gate — the APU.

The Takeaway

An airliner never relies on one source of power. Engines, the APU, batteries and an emergency propeller all stand ready — so the systems that matter always have electricity.

Sources

Keep reading

Backup Systems: A Spare for Everything That Matters

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Jet Engines: How They Work and Why They're So Reliable

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Common Flight Sounds Explained

A guide to every sound you'll hear during a flight — from boarding to landing — and what each one means.

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