Definition
A single rocker-style cockpit switch that controls both the battery master circuit and the alternator field circuit together, with two operating positions: ON (both battery and alternator energized) and OFF (both de-energized). Unlike a split master switch, the two halves cannot be operated independently — moving the rocker controls both circuits simultaneously.
Plain English
One switch that turns the battery and the alternator on or off at the same time. It only has two settings — on or off — so you cannot run the battery without also running the alternator, or the other way around.
Context Anchor
Seen in electrical-system procedures, especially when managing an alternator failure or conserving battery power in instrument flight.
Derivation
“Rocker” refers to the way the switch moves: it rocks from one side to the other, usually between ON and OFF. “Master” means it controls a main part of the aircraft’s electrical power, not just one small device.
Why Pilots Care
It is the single point that supplies all electrical power; an incorrect position or failure removes power to flight instruments, radios, and navigation equipment.
Intuition Check
Do not read “two-position” as meaning there are only two electrical sources. Here it means the switch has two selectable positions, usually ON and OFF. Do not read “master” as meaning it controls every possible electrical problem. It is the main power control, but the exact effect depends on the aircraft’s wiring.
Example Sentence 1
On aircraft with a two-position battery master/alternator rocker switch, the pilot cannot isolate the alternator independently during an overvoltage event.
Example Sentence 2
During a total electrical failure the pilot verified the two-position battery master/alternator rocker switch had not been bumped to the OFF position.