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Yep, that’s a chunk that broke off this magneto’s mounting flange. And as we talk about in today’s episode, when that mag fell out of the back of the engine, the airplane immediately became a glider.
So, are these “dual magnetos” a good idea, or a bad idea? I’m sure there are lots of opinions, and I’ve got one too. But don’t take my word for it… do your own research, and see what conclusion you arrive at.
Here’s the difference between the old style magneto attaching clamps in the bottom of these pictures, compared to the much better attaching clamps in the tops of the pictures.
In today’s podcast, we discuss 4 different stories related to this issue of “dual magnetos.”
The picture at the top of this post is the dual magneto from this Piper that had to land in a field back in 2008. Thankfully, there was minimal damage, but a landing gear door was also damaged in addition to needing a magneto. And since this particular airport had minimal maintenance facilities available, we ended up fixing everything outside… not the most ideal, but we got the job done!
Another story is of a Mooney I worked on and found the wrong gasket installed on the dual magneto, and the mounting nuts undertorqued.
And one more story of another Mooney, and the accident report from the dual magneto failure… thankfully, only minor injuries in that accident.
Finally, my most recent reminder of how critical it is to install dual magnetos correctly, is this Piper Lance. Listen to the podcast to find out why this airplane would not develop full power, and the EGT’s were ridiculously high for such a low power setting.
So, if you have a dual magneto (2 mags in one case, driven by one gear,) here are some recommendations to consider, so that you can operate as safely and reliably as possible:
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- Make sure the correct gasket is installed. P/N LW-12681, a round gasket. (Not an oblong gasket with holes, for mags that have flanges.)
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- Be sure the correct attachment clamps are installed. Take a look at the pictures for the old style clamps and new style… make sure you have the new style, P/N 66M19385. They are easily identified by the oblong ends, that cover more surface area where they contact the magneto flange.
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- Be sure the torque is proper. Ask your mechanic what torque was used for the magneto attaching nuts. Last time I checked, it was 204 inch pounds… I’ve found numerous mag attach nuts undertorqued. By the way, if your mechanic gets offended when you ask this question, it might be time to go somewhere else. I welcome this kind of question… after all, your safety and the safety of your passengers, depends on it!
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- Be sure there is torque putty on the attaching nuts, and check it frequently, to look for any movement. My favorite is Fluorescent yellow.
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- Do the recommended 500 hour magneto inspections. Make sure it’s done by a reputable shop… we either send mags out, or get an exchange one. Don’t take chances with such a critical component.
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- Consider modifying your engine to 2 single magnetos, especially at overhaul.
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- For me personally, don’t buy an airplane with a dual magneto… just my opinion.
- Print and keep these 2 documents with your maintenance records, and hand them to your mechanic whenever you are having dual magneto maintenance done.
Lycoming Service Instruction 1508C:
https://www.lycoming.com/sites/default/files/Dual%20Magneto%20Attachment.pdf
Special Airworthiness Information Bulletin (SAIB) NE-08-26R2 :
https://www.askbob.aero/sites/default/files/ne-08-26r2.pdf
And, one more article if you want to dig a little deeper and learn a little more about dual magnetos:
http://mechanicsupport.blogspot.com/2008/08/bendix-d3000-magneto-redundancy.html
Finally, if you are interested in learning more about how CHT’s and EGT’s are related to mag timing, check out some of Mike Busch’s excellent articles at SavvyAnalysis.com
Let me know what you think about today’s episode… whether you agree with me or not, I’d like to hear from you, so please contact me with your thoughts.
Email: dean@airplaneownermaintenance.com
Or, leave a comment on this page, or even better yet, leave me a voice message by clicking the button over to the right.
And if you appreciate the podcast, please leave a rating and review over at iTunes.
Thanks, and have a great weekend!
No need to scare owners of dual mags. Several years ago I checked the NTSB files and there was very little difference in the accident rate between dual vs two single mags failure rate. Of course the precautions you mention are worthwhile.
Thanks Paul. You might have a good point there. My main goal with this episode is to help prevent any problems with the dual mags that are operating out there.
So on my 1977 Piper Lance with the Bendix dual mag, I am again having a mag problem. The engine has 12 hours on it since overhaul by Zephyr Aircraft Engines. After a flawless 3 hour flight and topping the tanks, the engine started easily but on taxi to take off, the engine was extremely rough, surging and finally quit even though changing tanks, adding fuel boost, changing mixture had no effect. We immediately went to maintenance hangar and checked: fuel injector nozzles, spark plugs, wires, external timing, air filter and all checked OK. Another run up showed same problem although full RPM could be achieved with minimal roughness. Zephyr then recommended checking the mag since the second runup showed the engine ran well on the left mag while the right mag was intermittently rough.
Externally, the mag looked normal although internal exam showed the right points seemed more pitted than the left. The right capacitor showed 13 ohms resistance while the left capacitor was zero. After cleaning up the right cap connections, the resistance fell to zero. Engine was runup and it ran normally on both, left and right mags.
This is the second time a newly overhauled mag on a newly overhauled dual mag engine has caused near catastrophe. Fifteen years ago, the right capacitor burned out at 5 hours in flight and the right points burned severely causing failure but the left magneto ran well. The only indication was the expected increase in EGT running on one mag. Installing a new cap on the right mag fixed the problem. Ironically a few weeks later (1999) an AD came out telling of a bad batch of capacitors and they needed to be removed. Overhauler at that time was Teledyne and they sent another OVH magneto as I was stranded away from home. That mag ran flawlessly for 500 hours until I had it sent away for inspection; no unusual anomalies found.
So now my Lance is AOG while Zephyr Aircraft is sending another overhauled magneto for replacement. Let me say at this point that Zephyr Aircraft has been outstandingly supportive of my predicament even though they could deny any warranty based on hours. Incidentally, the magneto was overhauled by Quality Aircraft Accessories, another facility with a great reputation.
I agree with Dean: I am not a fan of the dual mag and considered changing to two separate magnetos during the recent engine overhaul but that would have entailed another~ $10K on top of a $33K overhaul plus a bunch of STC paperwork. But such as it is.
Going to 2019 AirVenture last week, I visited booths for magnetos looking for an STCed electronic dual mag. SureFly does not have one, ElectroAir has one in development, and I’m not sure what E-Mag has on their R & D bench. So I guess I’m stuck with another overhauled D3000 magneto. Maybe the included maintenance manual will have a preflight chant to the patron saint of magnetos for better reliability. And I’ll rely on Lycoming SI 1508C for correct installation.
Anyone else have other ideas or suggestions, please post them.
Ramon,
That is frustrating for sure.
Is Zephyr also sending replacement capacitors, or just the mag? When we send dual mags to Kevin at Aircraft Ignition Services in Texas, he wants to also check the capacitors. I’m not sure a standard ohm check is adequate for those. I’d recommend calling Kevin and talking with him about your situation.
Also, take a real close look at your P-leads. I’ve seen cases where the wire insulation cracks near the attachment to the magneto, and causes the P-lead to short out to ground. Sometimes this can be an intermittent problem… very frustrating.
Let me know how it turns out. Here’s Kevin’s number: 903-378-7205 http://aircraftignitionservices.com/contact-us/
Dean
This statement is a bit of a ‘math trick’. Accidents due to mag failures are rare. If 1/10 of one percent of accidents are due to mags of all sorts, and that rises to 1/5 of one percent when only dual mags are considered, it is both fair and true to say that “there is very little difference”. After all, it has risen only a fraction of a percent, right? And, I’m sure that most crashes of dual mag equipped aircraft are still “pilot error”. If a dual mag equipped Pa31 looses an engine because the mag fell out, and that guy crashes, even that is pilot error. I say that because most dual mag aircraft I’ve dealt with happen to be Navajos. Regardless, redundancy and tolerance for mechanic error are reduced, and in the above scenario, the risk has doubled…while also being “a slight increase”. Redundancy is good in aviation.
Hello greetings from Peru, we work witht enstrom helicopter, with a Lycoming HIO 360 engine, we haven’t had any issue with mags attaching nuts until now, the bad thing with dual is that they are harder to sync very well, thanks for your podcast, it’s the first time that I got in this webpage, it is interesting, I will subscribe to your YouTube channel.
Hello David! Great to hear from someone in Peru!
Hello Dean,
Here we are during quarantine and nine months after my original problem. Zephyr had T&W Electrical Services send a rebuilt magneto at that time. Nothing else was changed or done. I now have 75 SMOH and have had almost no problems after the magneto change. Almost. I notice mild stumbling on the runup noticeable 1400 to 1800 RPM. But cruise to max RPM has no problems. All temps, fuel flow, power seem to be normal. Still, the low RPM stumble seemed to persist. I removed the magneto and interestingly, a teaspoon of oil came out of the mag when I took the cap off. I have been told this is abnormal and there should be no oil in the magneto so I sent this 75 hour magneto back to T&W for an inspection as the left mag drop was way more than the right mag: 130RPM versus 70 RPM. Mag shop say their inspection showed the left points “slipped” a few degrees but otherwise nothing else seemed amiss inside. No answer was given as to why there would be engine oil inside the mag.
Other thought was given to the RSA10AD fuel servo contributing to the problem since the fuel flow at cruise would vary by 2-3 GPH at cruise when leaned. But AirFlow Performance who did the servo overhaul 75 hours ago, said the problem was not in the servo itself but maybe air getting into the supply side of the fuel pump, or a faulty fuel transducer. FlowScan said this was extremely unlikely as their sensors run thousands of hours before problems develop.
So the current plan of attack is to re-install the magneto, check all the fuel lines for air leaks, clean the injectors and see if there’s an change.
Dean, suggestions?
Hi Ramon,
I agree there should be no oil inside the mag. Perhaps it needs a new oil seal on in the drive end of the magneto.
As far as the stumble and the fuel system, that’s hard to say what’s going on there… one thing you might do, is pressurize the induction system with a small amount of air pressure and check for induction leaks with soapy water… check the intake gaskets and the other end of the intake pipes… the couplings if you have that type, or the orings if you have that type. Let me know how things turn out.
As a student pilot flying a rental 172 to pick up my instructor, I had a dual mag fail at 1200 hours of time. I was on short final and my last power reduction was when it failed. Made the runway and pushed the plane to parking.
So yeah, I agree with hour assessment, Dean. Love the podcast!
Thanks for your story Kent! I’m glad you were able to land safely!
I’m retired now, but maintained a fleet of club aircraft for 25 year which included two Mooney’s with the Bendix dual mags. Never had any problems (dual mag) problems in about 15,000 flight hours of training and cross country flight in Mooneys. Had 2 coil failures during that time which were each discovered by a pilot doing a run-up before flight. We kept a supply of parts so occasionally changing out a coil was not a big deal. Did 500 hour inspections in house with no problem.
We had about a dozen other aircraft all on Slick mags and with about 4,000 hours per year never had any problems* with them either (and they were a breeze to work on compared to the Bendix duals.) (That is until Champion bought the line and cut manufacturing corners, which I understand that they have now worked out.)
Thanks for your thoughts John! That’s good information.
Almost 30 years of working on Continental (Bendix) and Champion (Slick) mags here. The 2000/3000 series dual mags have always had small issues that other mags don’t have due to their design. The capacitors are not mounted in the magneto housing, so installing a mag and capacitors after 500 hour inspection (Yes, send the capacitors in as well!) requires the installer to check the resistance between the capacitor outer shell (the threaded terminal outside of the harness cap) and the magneto housing. This value needs to be as close to 0.0 ohms as possible. Dirt, paint, or a poor pressurization gasket on turbocharged engines can cause resistance that affects how the capacitors protect the points from arcing, I’ve seen many dual mags with melted nylon points followers due to the points overheating and the nylon melting against the spring, usually due to a poor ground between the capacitor and mag housing, or a failed capacitor which can only be tested with a capacitor tester.
Good info Scott… thanks!