Definition
The cockpit control that selects which magneto or magnetos provide spark to the engine's spark plugs and that activates the starter. Typical positions are OFF, R (right magneto only), L (left magneto only), BOTH, and START. In the START position, the switch energizes the starter motor while keeping the magnetos active so the engine can fire and run.
Plain English
The key-operated switch a pilot uses to start the engine and to choose which set of spark-producing units is feeding the spark plugs. It is the aircraft equivalent of a car's ignition key, but with extra positions for testing each spark source separately.
Context Anchor
You use the ignition switch during the before-start and engine-start checklist, and you may check it again during shutdown to make sure the ignition is off.
Derivation
Ignition comes from the Latin ignis meaning fire. The switch is named for its job of starting the fire (combustion) inside the cylinders by triggering the spark.
Why Pilots Care
Ensures reliable engine starting and prevents the engine from running with improper magneto settings that could cause damage or unsafe operation.
Intuition Check
Do not assume the ignition switch is just an airplane version of a car key. In many piston airplanes, it also selects the spark source, such as LEFT, RIGHT, BOTH, or OFF.
Example Sentence 1
After confirming the area was clear, the pilot turned the ignition switch to START and the engine fired on the second blade.
Example Sentence 2
After landing, the pilot moved the ignition switch to OFF to shut down the engine.