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2 Answers

Cycling magnetos during magneto check

Asked by: 1811 views Aircraft Systems

When you cycle the magnetos to check for RPM drop in a Cessna 172, why must you go from both to right back to both, than both to left back to both. When you go from both to right, you are passing over the left magneto selection, why not just do the left magneto first? Is there a reason why you must go to the right selection before the left?  Thanks in advance.

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2 Answers



  1. Kris Kortokrax on Feb 23, 2015

    When you check the mags, you are looking to see how much each one drops off. You are also checking to see the difference between the drop for left vs. right. By going back to Both, you can make sure that the throttle has not crept off your target setting.

    You are not just checking to see if the engine keeps running on each mag.

    I also perform a check prior to shutdown. With the throttle at idle, move the switch quickly from Both to Off and back to Both. If the engine doesn’t quit while on Off, then the P lead for one of the mags is disconnected and the mag will be hot when the engine is shut down.

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  2. Brian on Mar 01, 2015

    “I also perform a check prior to shutdown. With the throttle at idle,”

    Hopefully with the radios off as well. 😉

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