Magneto failure

Two-seat R22 and four-seat R44 helicopters.

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tanglefoot
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Magneto failure

Unread post by tanglefoot » Thu Jun 20, 2013 2:15 pm

I had an interesting experience this last week.

I flew down to KZN last thursday and landed at Emoyeni. All good, no problems. On the friday afternoon I landed on 'table mountain' and after a short walk around we climbed back in and I restarted. On doing the mag checks there was a slightly larger drop (still within limits) than what I was used to but after checking a few times I lifted and returned to Emoyeni. I had experienced a similar slight drop before but mainly on the first start, when she was still cold.

On Saturday afternoon I was preparing to take some friends for a flip. Started normally but on mag checks the right mag caused significant backfiring. Not much of a mag drop but the backfiring was uncomfortable, even with my ANR headset on. Powered down, offloaded pax and talked to some of the pilots there. Suggestions included Mag failure, plug failure (seemed to be missing on 1 cylinder only) and possibly moisture somewhere (A lot of dew in the morning. Was still dripping out of the door when we started up) Based on the feedback I restarted her and put her in the hover for 10min on both mags. On touchdown a retest showed everything ok. I shut down for the night and went and had a beer (or two)

On Sunday afternoon I thought I would recheck. Started up. No backfiring this time but definitely not firing on all cylinders. Tried the hover trick on both mags but didn't work this time. Shut down and started worrying about how to get home. Had a beer (or two).

Tried to call my AMO, no luck. Received a contact number for someone at JNC in Durban but no luck there either. It was Sunday after all and monday was a public holiday. Bryan at Emoyeni managed to convince a mate of his who worked on Lycomings to come out and take a look but I was still not happy as the repair would not be certified. As luck would have it one of my Model Aircraft Precision Aerobatics mates turned out to be an AME and he had a mate who was certified on Robbies. All set for Monday I had a couple more beers.

Monday came and Ronald from http://www.greystonesaviation.co.za arrived. I showed him the problem. He poked, prodded. We restarted and it just got worse. More poking, prodding. Now she won't start at all. Anyway, he removes the Magnetos and goes away, promising that he will be back latest Wednesday morning. Tuesday 1pm, 24hrs later, he calls to say that he is on his way. Arrives 2pm, mags fitted by 3pm and test flown by 3:30pm.

Can't ask for better service than that!!!!!!!!!!!!!!!!

A couple of lessons for me.

1. The massive degradation of the mags over a short period of time stunned me. When the problem first arose I considered the possibility of flying her to the nearest AMO on one mag. I'm glad I didn't do that.

2. In hindsight the problem had been brewing for longer. After the last 500hr inspection the CHT suddenly started running hotter than previously. When discussed at the time it was agreed that the gauge was still in the green so all ok. Now 300hrs later with the points replaced and timing reset the temperatures are back to their OLD normal. It is possible that at the last service the timing was not set correctly and maybe contributed to the faster deterioration in the points and condenser failure.

Next time the CHT is higher than normal I will know where to start looking.

Thanks again to Ronald and Greystones Aviation Components for sorting me out so promptly.
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tanglefoot
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Re: Magneto failure

Unread post by tanglefoot » Mon Jun 24, 2013 10:14 pm

Captain wrote:you say he took the mag's away? returned with them? what was the issue? I fly a R44 periodically and once about 6 years back had a BF on start up and it stripped a tooth on the mag pick up gear?? its made of industrial plastic ( i think I cant remember, been very long since I did the course on Robbies -Im not a AMo just a hobbyist pilot with a great interest in Helicopters, and other strange flying things)

The problem was not immediately apparent, as you say mag drop on start up and all that seemed normal, but it got worse and was found by the AMO during 100 hour interval service..
PS Biggles se ek moet saam met jo kom vlieg as ek weer in josie is :?: he say you scared him :lol: :lol: :lol: :lol: :lol: but then he is a Jabi pilot
I saw the plastic gear on the mags. Commented on it but it was not a broken tooth. From what I was told and what I could see the points were wearing unevenly. It appears that ultimately the points on the right mag were either welded shut or failed to close. I suppose that next time I'll pay more attention but I guess I was too busy watching, not looking enough! I think that the death knell was the capacitor failure.

If I had to take a guess I would say that the 500hr MPI (When the mags are redone) was not done correctly. The mag synchroniser was removed before the mags were retorqued and the timing was out. Possibly the points were inspected and not replaced although I can not think of a good reason why they could not just have replaced them. Unfortunately the points are a "on condition" item so the AMO gets away with (near) murder. Fortunately I picked up the problem on the ground.

I left the spares in RUT. When I get a chance I'll have a closer look.

Not usual to pick up Mag problems on a 100hr service. The AMO must have looked EXTRA hard.

I didn't frighten Biggles [-( I think it was the PC12 climbing out of Rand on 35 with an early left hand turnout (at night) that frightened Biggles (and me). Not sure why there was traffic on 35 after dark, not normal practise from what I have experienced :? We were inbound over Bruma ridge and descending. We saw it passing just ahead and slightly below when ATC came on line to warn us of traffic. I remember telling ATC that we had missed it but got no response [-o<

You're welcome to give me shout when you are in town. I'll do my best not to scare you too 8-[

PS: Have you seen the peaceful thread (viewtopic.php?f=59&t=62827#p727872) That is where the Jabi connection all started :lol:
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Re: Magneto failure

Unread post by tanglefoot » Tue Jun 25, 2013 3:00 pm

Captain wrote:Sweet... i flew in a Jabi once (as in one cct) lets just say i was very glad to be back on the ground, :lol: Im not the biggest of oaks but as you will know when we look down we like to see more than our feet :) or a dirty carpet so to speak so seeing the inside of the cab and bumping up and down..... well when i was younger it was fine almost normal as one gets used to flying only real aircraft ..... things with spinning wings seem so much smoother :) :) safer
Yea, any aircraft that has to be fitted with brakes in order to stop doesn't sound like a good idea :wink:
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Re: Magneto failure

Unread post by tanglefoot » Tue Jul 02, 2013 8:12 pm

Funny how there is suddenly a thread or two with "backfires", "missing" and loss of power. Everyone seems to home in on mixture, fouled plugs.

With my new found knowledge I would suspect the mags everytime. The damn thing is stuffed full of moving parts, some plastic, and if anything is going to go wrong with setting fire to the fuel in a cylinder then THAT is it.
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