Mag check issue

[bonal]

Coming home I did a quick mag check in flight and did not notice a change when on the left mag indication. When I reached the hangar I selected off to check and engine continued to run. Thinking about the pre flight run up I thought there was a drop but only very slight. Right mag gave me a 75rpm drop.  I know this has something to do with the p leads but cant remember what the details are if its grounding or not grounding or what. I know this is a not too uncommon problem. Thanks in advance for any information leading me to diagnose and solving this problem.

[DonMuncy]

The P lead is disconnected, or broken. Be VERY careful until you get it fixed. The mag on that side is hot.

[bonal]

As long as the prop is not moved it won't start on its own will it. I know this sounds stupid but just want to be safe until it's fixed. Should I disconnect the bat or will that make no difference.

[Andy95W]

You may want to put a sign on the prop that says HOT MAG-DO NOT MOVE PROP and make sure you keep the keys out of the ignition.

Luckily we don't have impulse couplings.  It is unlikely that without the shower of Sparks energized that the engine could fire.  Unlikely, but not impossible, so as Don said, be careful.

[bonal]

Thanks guys, I called my Hangar partner and let him know there is a hot mag.

[MHemperly]

If the p lead is not broken, the end of it inside the mag may just be worn... I've soldered the tip of it to build it up so it makes better contact. Consult a mechanic of course. Good luck! 

[Hector]

Battery will not make a difference. Just don't move the prop. If you keep the plane in your own hangar should not be a big deal until you get it fixed. If in a communal hangar where other folks my inadvertently handle the plane then you my want to take other precautions


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[Seanhoya]

Am I the only person scratching his head on this one?  Just wondering about the benefit of doing a mag-check in-flight?  Doesn't the risk (engine failure) outweigh any diagnostic benefit?

[Guest]

6 hours ago, bonal said:

Thanks guys, I called my Hangar partner and let him know there is a hot mag.

Open the 2 side cowls and look at the back of the magnetos for a broken wire.  Depending on the model the P lead may be a 3/4" nut with the wire passing through the centre, some have a small round knurled aluminum nut, or may be a small stud with a ring terminal on the wire and a 3/8" holding the wire on.

Clarence

[gsxrpilot]

1 hour ago, Seanhoya said:

Am I the only person scratching his head on this one?  Just wondering about the benefit of doing a mag-check in-flight?  Doesn't the risk (engine failure) outweigh any diagnostic benefit?

 For those of us who have attended the APS course in Ada, OK, we know that in-flight mag checks are much more useful and accurate than a mag check during run up. I now regularly do an inflight mag check at the top of decent on any cross country flights. 

The mag check at run up will show up problems, but not very accurately. You might have a fouled plug, but which one, you might have a broken p-lead, or just a weak mag. You really don't know.

An inflight mag check at cruise power with a proper engine monitor will tell you exactly what the problem is and if it's a plug or two, it will tell you exactly which ones.

[Guest]

A mag check on run up before flight is still important in determining correct operation.  It still identifies troubles.

Clarence

[bonal]

5 minutes ago, M20Doc said:

A mag check on run up before flight is still important in determining correct operation.  It still identifies troubles.

Clarence

Yes it does

[Marcopolo]

First off, Happy New Year Paul and all you other mooney spacers.

 

Second, I am going to try to attend the APS course, but haven't yet and I really am not just hunting posts from Paul to send a counter point out to.  In fact in the case of this post, my mag problem might have gone un-noticed for much longer if I hadn't done an in-flight mag check, but I will jump in here on the side of only doing mag checks on the ground unless the APS folks can give me advice on what to do if one mag is mostly or completely dead and my engine shuts off during the in-flight check.  There are some very important procedures to follow if the engine quits during a mag check, ones which if not followed could ruin an exhaust system, turbo, and some induction parts.  I would much rather this happen on the ground than at cruise.

 

  Where I will disagree with Paul is that my engine monitor only works at cruise settings, I believe it works the same on the ground as it does in the air, I will agree that you need to perform the ground run-up in a different manner to see some of the diagnostic information.

 

  My Magneto issue was due to the incorrect carbon brush/spring installed during a 500 hour mag overhaul.  The carbon brush was almost a quarter of an inch shorter than the proper part, this worked fine for approximately 120 hrs and then the even shorter length(couple thousandths of an inch from normal wear) started to cause dead spots throughout the rpm range, engine at idle would only be running on one mag, during run-up 1700-2000 rpm it would seem perfectly fine, cruise rpm it would shake your teeth outta your skull if you switch to that mag, on both in all cases...all seemed and felt normal.

 

Now I do a quick mag check at idle as the engine warms up, only looking to see if thy are both operating.  I then do a normal run-up prior to departure but add an almost full power mag check on the first flight of the day.  In-flight mag checks, for me, are useful but the down sides far out weigh the diagnostic returns...that is until APS can put my mind at ease.

 

First round is still on me Paul!

 

Ron

[ArtVandelay]

4 hours ago, Seanhoya said:

Am I the only person scratching his head on this one?  Just wondering about the benefit of doing a mag-check in-flight?  Doesn't the risk (engine failure) outweigh any diagnostic benefit?

I only do it when I'm over an airport, one with a tower and a long runway, because of the risk. I also switch fuel tanks only when I'm above an airport or at least a suitable landing spot, figuring there is some risk in that operation as well.

[bonal]

26 minutes ago, teejayevans said:

I only do it when I'm over an airport, one with a tower and a long runway, because of the risk. I also switch fuel tanks only when I'm above an airport or at least a suitable landing spot, figuring there is some risk in that operation as well.

Same here except the tower part.

[gsxrpilot]

3 hours ago, Marcopolo said:

First round is still on me Paul!

I'm looking forward to it!

A bit of clarification on my part... I believe the engine monitor is still useful on the ground, and so are mag checks during run up. But post APS, I now know how much MORE useful they are in the air. Prior to APS, I was right there with you. I was afraid of the possible consequences of the inflight mag checks, running a tank dry, switching tanks over inhospitable terrain, etc. The APS class taught me so much about how the engine operates, how to read that operation, how to listen and to understand what the engine is telling me, etc. that now I'm very comfortable with all of the above in-flight operations. It was a difference of my perceived risk based on my own ill-informed perceptions vs. actual risk based on solid knowledge and full understanding.

I like to think I put heaps of thought into every dollar I spend on aviation, other than 100LL. And for me, with my very limited experience and understanding, the APS class was likely the best money I've spent on aviation since buying a plane.

And I'll certainly buy a round for any of you guys anytime.  Happy 2017.

[Andy95W]

17 hours ago, Seanhoya said:

Am I the only person scratching his head on this one?  Just wondering about the benefit of doing a mag-check in-flight?  Doesn't the risk (engine failure) outweigh any diagnostic benefit?

I don't understand why the engine would fail just by doing a mag check on a reasonably well maintained airplane.

[carusoam]

Risk management techniques...

1) all the hardware is designed to be switched in flight.  Fuel tanks, mags, and batteries (LB Mooneys), radios etc...

2) Wear takes its toll. These things can fail miserably in mid flight.

3) Some people elect to make those changes with an extra Plan B in mind.  Switch over or near an airport...

4) Others buy newer machinery to alieve the thought of Stuff wearing out.  This may only help them feel better, it may not actually change their statistics...

How does that sound?

Best regards,

-a-

[ArtVandelay]

2 hours ago, Andy95W said:

I don't understand why the engine would fail just by doing a mag check on a reasonably well maintained airplane.

If you have a bad mag and switch off the good one, or the switch itself fails. Is it low risk, yes, but personally I try minimize when possible, because low does not equal zero. We accept a certain amount of risk but it seems silly to me not to try to minimize it by simply having a plan B, just in case Murphy's law comes into play.

 I can't believe APS wouldn't agree and recommend doing in flight mag checks without a thought of what to do if something goes wrong. 

[Guest]

18 hours ago, teejayevans said:

I only do it when I'm over an airport, one with a tower and a long runway, because of the risk. I also switch fuel tanks only when I'm above an airport or at least a suitable landing spot, figuring there is some risk in that operation as well.

If I was that worried about mag checks and switching fuel tanks, I'd have to get a different hobby.

Clarence

[Ned Gravel]

I scared the living daylights out of my PPP safety pilot during the MAPA PPP course this year by doing in flight mag checks after reaching 2500' - cruising altitude.  He was less worried when I explained it to him.  I trust the results of a mag check on the ground for the operation of my engine at 1700 rpm.  I trust the results of the inflight mag check for the operation of my engine at 2500 rpm.

 

[bonal]

Ok so going to look today and hope to get fixed. My question is if the ignition key is on the left mag indicated on the panel and there is no change in rpm which mag has the bad P lead pilot side or pax side. 

[DonMuncy]

It is a wire from the magneto coil to a ground, when the ignition key is turned off. When grounded, the coil can not produce a spark.

6 minutes ago, Hyett6420 said:

What is a P lead, is that the lead that goes from the magneto to the sparkplug?  

 

[bonal]

1 minute ago, DonMuncy said:

It is a wire from the magneto coil to a ground, when the ignition key is turned off. When grounded, the coil can not produce a spark.

 

Yes this I know my question is if the key is aligned with L which is giving no rpm drop which mag is not grounding pilot side or pax side. I'm thinking that when checking mags and the key is on one L or R that is the one that should be grounded and you are running on the other. I hope I'm making sense since this has always been kind of deslexic to me.

[DonMuncy]

1 minute ago, bonal said:

Yes this I know my question is if the key is aligned with L which is giving no rpm drop which mag is not grounding pilot side or pax side. I'm thinking that when checking mags and the key is on one L or R that is the one that should be grounded and you are running on the other. I hope I'm making sense since this has always been kind of deslexic to me.

It has always been dyslexic to me too. You can read up on it, or check with an ohmmeter.