What are mag failure symptoms?

The recent report of a PMag failure shows that in at least that case rough running and very high CHTs can be one symptom of a PMag failure.

I did have a Bendix mag impulse go out and the engine would not start. I also had a Lightspeed problem which I think was a connector corrosion problem. No problems with either system in-flight in about 1400 hours.

What are typical characteristics of possible failures of Bendix, Slick and Lightspeed systems?

Quiet-----lots of quiet.

Poor rate of climb.

Great GPH numbers.

ROTFLOL

that's a good one.

Ron Lee said:

What are typical characteristics of possible failures of Bendix, Slick and Lightspeed systems?

Click to expand...

I've been flying since 1967 and have had one mag failure. It was the impulse mag and the engine would not start. However, there's that beautiful hindsight in that the engine had been more difficult to start for the preceding several months! Duh! BTW, the mag that failed had an unknown number of hours. Probably close to a thousand.

It surprised me...

....when the perfectly trimmed Cessna Agwagon I was ferrying started a descent without me having changed anything. For some reason I decided to do a mag check and it quit on one mag. Retrimmed, it was ever so slightly slower...a surprise.

Stuff happens,

1 for me too..

I had a mag fail in a Citabria on the 2nd flight of the day. It ran fine 5 minutes earlier. I did a run-up(always do) and it just wasn't running right. Started into the mag check and sure enough it died completely on 1 mag. I was stunned. So, I went flying anyway

John

p.s. I didn't really fly it, it was a joke. So, save the hate mail

My Mag Failure

Like Pierre, I was flying a Cessna, an Ag Truck in this case. It was the first load of the morning, and the pre-takeoff checklist was completed and everything was satisfactory, including the mag check. So I pulled onto the runway and went to full throttle. Everything felt fine until I went past the departure end of the runway at about 100'. Suddenly things didn't feel quite right. There was a very slight vibration that was unusual, and the normal power didn't seem to be there. That was of concern because I had 200 gal. of spray in the hopper, and that can be a handful at 2200' elevation. I debated for a couple of seconds about continuing and trying to get rid of the load on the field, but in the end elected to return to the airport and make a way over gross landing.

After a successful landing, using a substantial portion of the runway, I taxied off the runway and did another mag check. It was perfect! So I sat there for a couple minutes thinking, then did a full power run-up. When I went to the left mag, the engine went deader than Elvis. So I went and woke up the on-field mechanic ( 0630 ). He took a look at the bad mag and said that everything was rusted and falling apart inside. He checked the other one, and it was about as bad. He is the one that did the annual on the airplane, so I don't know if he just missed the mags or what. I was not a happy camper.

I don't know if there is a moral to this story or not, except to pay attention to your instincts. If you feel there is a problem, there probably is. The in-flight indications of the mag failure were fairly subtle. Just a little bit of vibration, and a very slight decrease in performance. If it hadn't been for the vibration I would probably have put the performance decrease down to more moisture in the air than usual.

Ron Lee said:

What are typical characteristics of possible failures of Bendix, Slick and Lightspeed systems?

Click to expand...

Not sure about slick--I've never operated a plane with one AFAIK.

I've had two Bendix mag failures on the ground (engine wouldn't run at all on mag check).

Our airplane (I wasn't flying at the time) had a Bendix mag jump timing which resulted in detonation and significant engine damage. I'm aware of at least a handful of similar events in Bendix mag/6 cylinder TCM engines.

The lightspeed failures I've read about are mostly coil failures or connector failures which cause a coil to not fire, (loss of power in two cylinders). There are at least a couple of reports of Hall effect sender failures resulting in jumped timing.

One lightspeed failure was caused by rainwater getting into the box in flight (kind of hard to blame the box for that).

Bottom line for me:

any ignition can fail, there are only so many ways they can fail, have more than one, have a way to kill one that is misbehaving, and remember to check if the engine isn't running right.

Had a Slick fail in flight

In my old Grumman Tiger (O-360A4K) I had a left mag fail after about 20 minutes into flight. Passed ground checks fine, took off. First thing I noticed was the engine was starting to run slightly rough. At first it was subtle, but it was there. I had a non pilot passenger and he did not notice a thing, even when I mentioned it.

Over then next couple of minutes I did a number of things. I Looked at the EGT/CHT monitor and CHT was dropping (slowly so you had to know your temps for your plane and watch trends), EGT was rising - that was much more pronounced and immediate. First thing I did was adjust the mixture, while I could make it smoother - I could not make it smooth. Then I did a mag check. Turned from both to right and it ran EXACTLY the same. I said to my passenger that its likely to get quiet when I switched to left only and it did. I switched back to right only and flew to the nearest airport. It ran smoother on right only.

The reason the EGT was rising is without both plugs is was burning a small bit of the unburnt gasses in the exhaust header. The reason the CHT was dropping is the engine was not putting out as much power without both plugs working. Less power, less to cool.

Got on the ground and the mag was dead. When it cooled it would start (left is the impulse coupling side), but of course I would not fly it. It appeared to OK when cool, got unreliable when hot. New Slick and it was good to go.

I have a friend that had a Bendix fail recently. Similar indications. He did not kill the mag even after he confirmed it was bad (not a good idea) so he flew it home with it running rough. Best idea is to take the bad mag off line if you are sure whats going on.

Ron Lee said:

What are typical characteristics of possible failures of Bendix, Slick and Lightspeed systems?

Click to expand...

Back when I used to rent, I checked out a 172 at the local AP. I stopped at an airport about 25 miles away ran by the same FOB. As I got ready to leave, the plane wouldn't answer the mag check. I went back in and dropped the keys on the counter and said "It's broke."

"Fly it back and tell the maintenance guy," was the reply. "YOU fly it back! I not going anywhere in that. Give me another airplane." After some discussion, I won and they gave me their rental. The 172 made an emergency landing about half the way back. BOTH mags gone! Maybe we need three mags.

Bob Kelly

The parts that

wear are the tower and rotating contactor, and the points. Points erode and can effect how strong a spark is (mag drop). The rotating parts simply wear each other out and need to be replaced (misses at higher power settings). Bendix mags will typically go 500 hrs without trouble, then the tower and related parts should be replaced. The difference between a 500 hr inspection and overhaul is the attention given to the bearings. I personally don't care for Slicks, One A.D. at 250 hrs doesn't fit well with the 100 hr inspections I am doing on revenue aircraft, and my only failures have been Slicks. (one impulse coupling, other corroded points). As an A&P I can do the work but I send them to a shop that I trust. All he does is components, and the work I give him opens up all his experience to me if I need it. Magnetos are a sophisticated little workhorse. The internal timing needs to be spot on. For me, just because I can (and I have) doesn't mean I should.
I have invested in the manuals, and came to appreciate good regular maintenance from someone who sees a lot of them. For me, I won't let a Bendix mag go without a 500 hr inspection.

Andrew
-4 started and sold
flying 11AC Chief
A&P I.A. D.O.M.