Definition
In the context of an aircraft ignition system, START refers to the momentary ignition switch position that engages the starter motor and energizes both magnetos (often through an impulse coupling or starter vibrator on the left magneto) to crank the engine and produce the retarded, boosted spark needed for engine start. When the key is released, it springs back to the BOTH position for normal operation.
Plain English
It is the position on the ignition key — past OFF, R, L, and BOTH — that you turn to and hold to spin the engine over and light it off. As soon as the engine catches, you let go and the key snaps back to BOTH.
Context Anchor
Seen on key-type aircraft ignition switches during the engine-start checklist.
Derivation
Start comes from an older English word meaning to move suddenly or begin moving. That fits the aviation use: the START position is what begins the engine’s movement toward running.
Why Pilots Care
Selecting START engages the starter while ensuring ignition is active so the engine can begin running safely and reliably.
Intuition Check
START does not just mean “begin” in a general sense here. On the ignition switch, START is a specific switch position that engages the starter motor to turn the engine.
Example Sentence 1
With the mixture rich and the throttle cracked, the pilot turned the key to START and the engine fired on the second blade.
Example Sentence 2
Before turning to START, the checklist calls for setting the throttle to idle and the mixture to rich.