About the “R” and “L” on the Pro Flight Switch Panel rotary switch

The “R” and “L” on the rotary switch stands for the magnetos that are inside each engine. 

The magneto works basically like a generator. In simple terms, there are a bunch of wires in a coil around a bar, and a magnet spins around next to them whenever the engine is turning. The  spinning magnet induces a current in the wires, which is transferred to the spark plugs. This causes the spark plugs to fire and burn fuel, which keeps the engine turning, which in turn keeps the magnetos firing; this then becomes an infinite cycle until the magneto is switched off.

To reduce the probability of a magneto failure, modern piston engines have dual or two separate magneto systems (which is normally designated “left” or “right”), firing two separate spark plugs in each cylinder. Although both systems are normally used together, in the case of a magneto failure, one system is adequate to fly the aircraft to an airport where repairs can be made to the broken system.

Engine controls will include some form of switch system with which the magnetos can be switched on and off — individually or together. The type of switch varies from aircraft to aircraft, but is usually either a set of toggle switches for individual control (one for each magneto) or a rotary switch to control both (which may require a key to operate).

A rotary switch is used by the Pro Flight Switch Panel. The rotary switch has five settings: 

• OFF
• RIGHT
• LEFT
• BOTH / ALL
• START

When you turn the rotary key to the ‘R’ position, the right magneto of each engine will activate.  Turning the rotary key to the ‘L’ position will activate the left magneto.

When you turn the key to "Start" or the "Both/All" position, both magnetos are on and ready to go. Going to "Start" engages the starter, which gets the engine turning, and also turns the magnetos. They are timed to fire at exactly the right time in the ignition process.