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3 Answers

“Hot Mag Check” during shutdown

Asked by: 1024 views Aircraft Systems

Doesn't look like this has been asked here before... Where's the source documentation/recommendation/approval of cycling the mags to OFF and back to BOTH quickly prior to eng shutdown (O-320, O-360). I understand you're checking the ground integrity but this is not a PA28/C172 POH approved procedure. Just seems like a "we always do it" or "my last instructor taught me to do it" kind of thing. Again, looking for official/mfgr recommendation or approval. Thanks!

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3 Answers



  1. EAD on Aug 23, 2023

    Sometimes certain practices don’t have “official” recommendations/approvals. But they may be valuable regardless.

    Think about what information you gain by doing the check. If there is a “hot” mag this is your final opportunity to find it and squawk it before the aircraft gets handed off to someone else (potentially).

    If you didn’t do the check and had an undetected failure, someone could pull through the prop and have it “kick” at them, potentially causing an injury, or worse.

    This is just my opinion on the practice.

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  2. dudebro311 on Aug 23, 2023

    Found it. AC 20-106 states:

    If the magneto is not properly grounded, it is possible for the engine to operate, even though the magneto switch is in the “OFF” position. A check of this “OFF” position should be made a regular part of each engine shut down after each flight. BEWARE OF THE PROPELLER, even when the switch is “OFF”–especially when the engine is warm.

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  3. Kris Kortokrax on Aug 23, 2023

    Take a look at AD 76-07-12. It requires the check every 100 hours for the listed Bendix magneto switches. Per the AD text, it may be performed by the pilot. The check must be recorded in the aircraft’s maintenance records.

    https://drs.faa.gov/browse/excelExternalWindow/C14960A415D956BD86256E520053A53E.0001

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