Question about runup/mag. check

[oilcanbland]

Just a quick question. I'm sure it is the same for all small aircraft, but I'll just refer to the C152. Lets say that while you're doing a runup, you switch the ignition to the R position. Does that ground out the left mag or the right one? I thought that if you moved it to R, it would ground out the left mag, which means you'd be running the plane only on the right one. I was talking to someone in my class, and they disagreed with me. I couldn't find it in my POH. Just wondering.

 

[EagleRJ]

Yes, in the R positon, the left magneto's P-lead is shorted to ground, so the voltage it produces doesn't reach the plugs. The engine is running on only the right magneto.

 

[metrodriver]

I think the other person confuses it with a twin or other plane that has rocker type switches. If you switch off the left mag, and suddenly the engine has too big a drop, it is the right mag that's bad (the right mag switch is still on).