Sim/cockpit/engine/ignition on

From X-Plane SDK

This is an enumerated value for the "key" ignition in a prop-type plane. Left/right/both refers to the magnetos in the engine; generally a piston aviation engine has two separate sets of magentos to provide redundency.

As part of a run-up check you go from "both" (all 4 magnetos, std operating mode) down to left and right and in both cases observe a drop in RPM as half the magnetos stop providing juice to the spark-plugs...a lack of RPM drop means 2 were offline already and you shouldn't take off).

(More background: the electricity for sparking in a piston engine comes from the rotation of the engine, not the electrical system, so the engine can continue to generate spark and fire even after an electrical failure.)

0 - Off
1 - Right
2 - Left
3 - Both