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Thread: Runup magneto drop: Owners Handbook vs Lycoming Operating Manual

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    Runup magneto drop: Owners Handbook vs Lycoming Operating Manual

    For runup and mag check on O290-D2:

    PA-18-135 owners handbook calls for 1800 RPM and each mag to drop no more than 100 RPM. That's all it says.
    The Lycoming O290-D2 Operator's Manual states 1800 RPM, and no more than 175 RPM drop, and not more than 50 RPM differential between mags.

    I take it the Lycoming manual is the gospel?

    Prepping for checkride. Like to know the "correct" answer to these things.

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    Grant's Avatar
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    Quote Originally Posted by Cardiff Kook View Post
    For runup and mag check on O290-D2:

    PA-18-135 owners handbook calls for 1800 RPM and each mag to drop no more than 100 RPM. That's all it says.
    The Lycoming O290-D2 Operator's Manual states 1800 RPM, and no more than 175 RPM drop, and not more than 50 RPM differential between mags.

    I take it the Lycoming manual is the gospel?

    Prepping for checkride. Like to know the "correct" answer to these things.
    Go with the more restrictive for the checkride. If you think about it, there is no reasonable way the differential will be an issue if the max is 100 RPM drop on either....

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    Quote Originally Posted by Grant View Post
    Go with the more restrictive for the checkride. If you think about it, there is no reasonable way the differential will be an issue if the max is 100 RPM drop on either....
    yes- the issue is the engine mag drop is often more than 100rpm

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    skywagon8a's Avatar
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    Quote Originally Posted by Cardiff Kook View Post
    yes- the issue is the engine mag drop is often more than 100rpm
    Your magneto's internal timing needs attention. The points opening is not correct.
    N1PA
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    Quote Originally Posted by skywagon8a View Post
    Your magneto's internal timing needs attention. The points opening is not correct.
    but why the difference between the 0290d2 manual and the owners handbook?

    I also note the owners handbook is for both a -95 and -135- but it only lists one mag drop number for the two different engines- “no more than 100 rpm”

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    Upon further research it turns out the 175/50 is correct.

    Lycoming Service Instruction No. 1132B addresses this very issue:

    “Lycoming Operator’s Manual for O-290-D2 engines specifies 100 RPM maximum magneto drop-off when the engine is properly timed at 18 degrees spark advance. Since 100 RPM drop-off is sometimes difficult to obtain at this critical spark setting, it is recommended that spark plug gaps be maintained at .025 inch for best results. The 175 RPM maximum magneto drop-off is permissible.”

    https://www.lycoming.com/sites/defau...20Drop-Off.pdf

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    skywagon8a's Avatar
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    You are covered in order to take your check ride. After you are finished, get your ignition system tuned up. When an engine is operated at the described Limits, it is very inefficient.
    N1PA

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    Steve Pierce's Avatar
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    That owner handbook is not an official FAA approved manual. I had to point that out although it didn't make any difference to the FAA when they wanted to do performance testing and reach 35 mph and pull full flaps and climb like that manual says can be done.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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    skywagon8a's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    That owner handbook is not an official FAA approved manual. I had to point that out although it didn't make any difference to the FAA when they wanted to do performance testing and reach 35 mph and pull full flaps and climb like that manual says can be done.
    Is this why the repairs were needed?
    N1PA

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    Steve Pierce's Avatar
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    Number of things. Pilot had 30 hours of tailwheel, missed the test area, decided to drive to the runway after missing the test area, too fast, pilot induced isolation, stuck with it instead of going around and went in the trees.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Thanks skywagon8a thanked for this post

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    Runup magneto drop: Owners Handbook vs Lycoming Operating Manual

    Quote Originally Posted by Steve Pierce View Post
    That owner handbook is not an official FAA approved manual. I had to point that out although it didn't make any difference to the FAA when they wanted to do performance testing and reach 35 mph and pull full flaps and climb like that manual says can be done.
    Seems like the DER pilot didn’t have a test plan that was designed to show compliance to the regulations! The test plan should have only had test points that were required to meet specific regulatory requirements, and only those regulatory requirements that would be impacted by the change of propeller. Most STCs only need to show “at least equal to” the originally published data, not develop an entirely new performance section. Sounds more like he just wanted to go joy riding!


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    Last edited by dgapilot; 05-11-2022 at 06:23 PM.

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    Steve Pierce's Avatar
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    Quote Originally Posted by dgapilot View Post
    Seems like the DER pilot didn’t have a test plan that was designed to show compliance to the regulations! The test plan should have only had test points that were required to meet specific regulatory requirements, and only those regulatory requirements that would be impacted by the change of propeller. Most STCs only need to show “at least equal to” the originally published data, not develop an entirely new performance section. Sounds more like he just wanted to go joy riding!


    Sent from my iPad using Tapatalk
    FAA flight test pilot flying with FAA engineer in the back. It was a very detailed fight test but being that there is no data in the PA18 POH they came up with their own test plan which defied common sense to me. I pointed this out and it got kinda heated. The next day I was told if there was another incident like the previous day they would pull the plug. I stayed away till they tried to take off with the fuel valve out of detent, then lost a pencil and didn't get the seat latched.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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  13. #13
    skywagon8a's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    FAA flight test pilot flying with FAA engineer in the back. It was a very detailed fight test but being that there is no data in the PA18 POH they came up with their own test plan which defied common sense to me. I pointed this out and it got kinda heated. The next day I was told if there was another incident like the previous day they would pull the plug. I stayed away till they tried to take off with the fuel valve out of detent, then lost a pencil and didn't get the seat latched.
    I see the FAA's flight test department hasn't changed much over the years! We could spend many hours telling FAA test pilot stories around the campfire. The very first one I had dealings with was one of the good ones. After that, well ...............
    N1PA
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