Failed Magneto

[BillTIZ]

Is it standard practice or requirement to check the Magnetos during the annual inspection? And to what extent?

Just check for proper external timing?
Pull each mag and check the interior condition and timing?

Annual Inspection in February.
Right Mag failed today after flying 3 hours yesterday and on average about 5 hours each weekend since the Annual Inspection.

Mech pulled the mag, internal examination, points are seriously corroded.

Perfectly good flying day lost while parts are gathered.
Check ride scheduled for Monday, lost.

I'm beginning to think I got an incomplete Inspection?

 

[tonycondon]

i think they usually just check for operation and timing, unless an AD or something requires an interior inspection of course. Im sure the A&Ps here will have better answers.

 

[RotorAndWing]

An annual inspection only requires the checking of operation and correct timing. AD inspections are not considered as part of an annual inspection although they can be accomplished simultaneously.

 

[wabower]

My impression is that mechanics are taking a harder look at logs to determine time in service, primarily due to the recent increase in mechanical problems and failures.

 

[gismo]

Is it standard practice or requirement to check the Magnetos during the annual inspection? And to what extent?

Just check for proper external timing?
Pull each mag and check the interior condition and timing?

Annual Inspection in February.
Right Mag failed today after flying 3 hours yesterday and on average about 5 hours each weekend since the Annual Inspection.

Mech pulled the mag, internal examination, points are seriously corroded.



Perfectly good flying day lost while parts are gathered.
Check ride scheduled for Monday, lost.

I'm beginning to think I got an incomplete Inspection?

It's common but not required to open the magnetos every 500 hrs to check the condition of the points and rotor. I doubt that anyone does this on every annual for airplanes flown less than a few hundred hours per year. AFaIK the internal timing need not be anywhere near as precise as the "external" timing, slightly off just reduces the available spark energy a tiny bit.

 

[kmead]

I pull the magnetos every annual inspection and open them up for inspection. You couldn't believe the problems we find. I feel a part of my inspection is to help the engine make it through the next year without problems.

If you have a Piper, look at the inspection guide. All of the Piper guides reference inspection of the points and distributer contacts. I don't have x-ray vision and will need to open the mag.

When I do the Malibu seminars I tell the owners that they should just install 2 new mags if the shop wont open them up. It's a lot cheaper than sending the passengers home on the airline when it dies then going back to pick it up.

Kevin

 

[Dan Thomas]

It's common but not required to open the magnetos every 500 hrs to check the condition of the points and rotor. I doubt that anyone does this on every annual for airplanes flown less than a few hundred hours per year. AFaIK the internal timing need not be anywhere near as precise as the "external" timing, slightly off just reduces the available spark energy a tiny bit.

The manufacturers, like Slick and TCM (Bendix) call for 500-hour internal inspections in their manuals. TCM also calls for a four-year inspection. Corrosion happens whether the engine is run or not, especially in damp environments. There are unplated steel parts in these things and they do rust. I've seen the ball bearings corroded and falling apart in old mags.

We do the mags on our seven aircraft every 500 and usually find something going wrong to some degree. The points, for instance, are getting questionable by the time we get to 1000 hours. If the points cam wears (timing will show as retarded on the engine) or as the points pit (timing will show as advancing). Both of these will affect the internal timing, or "E" Gap, as it's known, and a couple of degrees off can weaken the spark a whole bunch. Typical E-Gap is 8 or ten degrees, and it's critical. See:
http://www.sacskyranch.com/egap.htm

Since spark is so critical, we pay sots of attention to mags. Even if they make enough zap to run the engine at idle, they can strand an airplane far from home if they're getting weak, since sooner or later they won't make enough spark to start the engine. It's false economy to avoid inspecting them.

Dan

 

[SCCutler]

My mags were both right at 500 hours last annual, and the mechanic was not remotely interested in sending them back out without a teardown and inspection, and knowing this was to be done, new points, condensers ($$$!) and cams were ordered and installed.

Given the relative simplicity of magnetos, the act of inspecting and cleaning them, and replacement of the referenced parts is wise and I considered it money well-spent. We may not be able to call them "overhauled," but they are certainly well-tended.

 

[Let'sgoflying!]

If I had recently inspected the mags, ie in the last 50 hours and less than 6 months ago I would not have expected the IA to look at them.

I have settled on this schedule for mags r&r:

every 250 hours
contactor points

every 500 hours
above plus
condensor
carbon brush
snap ring
seal, slinger
woodruff key, nut

1500 hours
above plus:
nylon gear
bearings and races
(need shims)
cam and screw
felt ring and strip

The impulse coupling AD on my Bendix (Bendices) is every 500hours for wear on the flyweight, axle, stop pin

 

[Dan Thomas]

If I had recently inspected the mags, ie in the last 50 hours and less than 6 months ago I would not have expected the IA to look at them.

I have settled on this schedule for mags r&r:

every 250 hours
contactor points

every 500 hours
above plus
condensor
carbon brush
snap ring
seal, slinger
woodruff key, nut

1500 hours
above plus:
nylon gear
bearings and races
(need shims)
cam and screw
felt ring and strip

The impulse coupling AD on my Bendix (Bendices) is every 500hours for wear on the flyweight, axle, stop pin

Some of those Bendix mags had issues with corroding impulse coupling springs. There was an AD on them years ago but there might still be a tendency to rust. If they corrode they can break, and when they break the timing goes to TDC and the engine's power output, if it's one of those dual mags, can drop to not much above nothing.

The condenser seldom makes any trouble. Slick sure charges a lot for a new one (around $80 CDN) and the distributor assembly is almost $300. Points (with cam) are about $30.

Dan

 

[AcroBoy]

I just had my Baron out of annual, and on the runup for the return trip the left mag on the left engine was completely dead, and needed replacement. Then, a week later, my Extra was in for annual, and it had a dead mag. Yet, both planes flew in just fine, and the runups were fine on the way to the mechanic. So, I guess it can happen, and I am sure it is not because something was missed at the annual.

 

[bbchien]

Yup. Coming back from C09 I had a normal runup, noticed the left engine EGT a bit high, did a cruise mag check, left engne left mag completely dead.

The bushing through which the shaft comes through was seriously worn, beating up the plastic continental gear.....

 

[BillTIZ]

Thanx for all the responses.
Yes.. I remember the 500hr inspection recommendations on the mags, we average about 200hrs a year flying every weekend.

Maybe it was just time to fail, I remember the left mag failed last summer. I thought we opened up the right mag at the same time. But maybe not.

 

[Tom-D]

Is it standard practice or requirement to check the Magnetos during the annual inspection? And to what extent?

Just check for proper external timing?
Pull each mag and check the interior condition and timing?

Annual Inspection in February.
Right Mag failed today after flying 3 hours yesterday and on average about 5 hours each weekend since the Annual Inspection.

Mech pulled the mag, internal examination, points are seriously corroded.

Perfectly good flying day lost while parts are gathered.
Check ride scheduled for Monday, lost.

I'm beginning to think I got an incomplete Inspection?

There is no requirement to do any thing to a mag at annual, other than to check the mag to engine timing, and the mag drop at out of inspection run to see performance.

All the inspections that are noted by others are service bulletin based and not required by part 91 operators.