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2 Answers

magneto check

Asked by: 8758 views Student Pilot

you have to cancel your flight if you find a more than 175rpm drop in magneto check or there is an alternative way to resume your flight?.i want to know is there any way to fix this error without asking a mechanic? your magneto is broken if  you find a more than 175rpm drop in magneto check?

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2 Answers



  1. Sam Dawson on Dec 09, 2013

    The more common cause of a magneto “failure” during run up is a spark plug problem, usually a fouled spark plug.
    First prevention. Lycoming has a procedure that they recommend for their IO-360 series engines but it can be used for any engine without harming it- you will actually help the engine. After start set your RPM to 1200. Then lean the mixture until the engine runs rough. Enrichen just enough to stop the roughness then set 1000 RPM.

    To “cure” the problem do a high power run up. Initially I will try about 2100-2200 RPM. lean for maximum EGT, then let it set for about a minute at this setting to “burn off the plugs”. If this does not work try a full power run up and lean the mixture again. If this does not work time to get a mechanic.

    If you have an engine monitor page or an engine monitor use it during the mag check as it will give more information than just an RPM drop. If only one cylinder is cold during the mag check then it is probably a fouled mag or bad spark plug. If all the cylinders are the same when you get a large RPM drop then it is probably a mag issue.

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  2. Sam Dawson on Dec 09, 2013

    Here is the Lycoming service instruction I referenced:
    http://www.lycoming.com/Portals/0/techpublications/serviceinstructions/SI%201497A%20(04-12-2011)/Engine%20Procedures%20for%20Flight%20Training%20Operations.pdf

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