Definition
A cockpit-mounted electrical switch, usually part of the master switch assembly, that connects or disconnects the alternator from the airplane's electrical system. When on, the alternator can charge the battery and supply electrical power to the aircraft's systems while the engine is running. It is often a split-rocker design, with one half controlling the alternator and the other half controlling the battery.
Plain English
The switch in the cockpit that turns the airplane's main electrical generator on or off.
Context Anchor
Seen during cockpit preflight, engine start, and electrical system checks, often near or combined with the battery or master switch.
Derivation
Alternator comes from the Latin alternare, meaning 'to do by turns.' The alternator gets its name because it produces alternating current — electricity that switches direction back and forth — before that current is converted to direct current for use in the aircraft.
Why Pilots Care
Turning the alternator switch on after engine start ensures the battery charges in flight; leaving it off or turning it off after a failure prevents electrical drain or damage.
Intuition Check
Do not assume the alternator switch and the battery switch are always the same thing. In many airplanes, battery power can be on while the alternator is still off.
Example Sentence 1
During preflight, the pilot confirmed the alternator switch was off before turning on the master.
Example Sentence 2
When the alternator failed in flight, the pilot turned the alternator switch off to isolate the system before continuing to the destination.