Definition
A condition in which the aircraft's alternator stops producing electrical power, leaving the battery as the only remaining source of electrical energy for the aircraft's electrical systems.
Plain English
The part of the aircraft that normally generates electricity has quit working, so the aircraft is now running only on what's left in its battery.
Context Anchor
Seen during instrument flying when a warning light, electrical gauge, or loss of electrical equipment shows that the charging system may not be working.
Derivation
Alternator comes from the Latin alternare, meaning 'to do by turns,' because the device produces alternating current. Knowing this helps explain why the failure of one rotating, engine-driven component can take the entire charging system offline.
Why Pilots Care
Loss of the alternator can lead to rapid battery drain, disabling electrically powered instruments, radios, and navigation systems needed for continued safe flight.
Analogy
It is like unplugging a phone from its charger. The phone may still work for a while, but only until the battery runs down.
Intuition Check
Do not assume an alternator failure means the engine has failed. It means the aircraft’s electrical charging source has failed, and the airplane may keep flying while battery power is still available.
Example Sentence 1
After noticing a discharge on the ammeter and a low-voltage warning light, the pilot suspected an alternator failure and began shedding non-essential electrical loads.
Example Sentence 2
In instrument conditions, alternator failure requires immediate action to keep essential avionics running on battery reserves.