Definition
An engine-driven electrical generator that produces alternating current (AC), which is then rectified to direct current (DC) by built-in diodes to supply the aircraft's electrical system and charge the battery. Alternators produce useful current at lower engine RPM than equivalent generators and are the standard charging source on most modern piston aircraft.
Plain English
The device on the engine that makes electricity while the engine is running. It powers the airplane's electrical equipment and keeps the battery charged.
Context Anchor
Seen in aircraft electrical system descriptions, cockpit charging checks, and alternator failure procedures.
Derivation
From 'alternate,' Latin alternare, meaning 'to do by turns.' The name reflects what it produces internally -- alternating current -- where the electrical flow reverses direction many times per second before being converted to DC for the aircraft.
Why Pilots Care
A failed alternator drains the battery and can cause loss of radios, lights, and instruments in flight.
Analogy
Functions much like the alternator in a car, turning engine motion into usable electrical power.
Intuition Check
An alternator is not the battery. The battery stores electricity; the alternator makes electricity while the engine is running.
Example Sentence 1
After starting the engine, the pilot checked the ammeter to confirm the alternator was charging the battery.
Example Sentence 2
When the alternator failed, the pilot shut down nonessential electrical loads to conserve battery power.