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3 Answers

Use of Mag switch

Asked by: 3666 views General Aviation

Would I harm a general aviation aircraft engine, like in a Cessna 172, when shutting it down, if I turn off the Mag switch immediately after moving the mixture to the cut-off position before the prop has completely stopped?

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3 Answers

  1. Jason Schappert on Oct 22, 2010

    Will this cause harm…. generally no.However OVER TIME (quite a bit of time) this is going to be hard on the mags (fly weights and other internals)Best practice is to turn the switch to off after the prop has stopped turning

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  2. Curtis Ide on Oct 23, 2010

    Quick add-on – It’s good to let the mags run until the engine is completely shut down to help ensure you burn/expend all the fuel that is coming into the engine.  Helps keep those bottom sparks plugs clean.

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  3. Brian on Oct 24, 2010

    Jason, would you mind elaborating on how that internal damage is caused? I am not well versed on magnetos and would be curious to understand this. Thank you.
    One more add from me — SAFETY! The mag switch grounds the magnetos and pulling the mixture empties the engine of all fuel. Combine, these two things prevent the engine from inadvertently starting. Leaving fuel in the engine now leaves you with only a 1/4 inch wire between life and death if that prop gets spun. Just a little corrosion on just the right spot on just the wrong day and… Well you get the idea. 
    Fly safe,

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