Strange mag issue

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Magman

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Magman
C-150 with Slick 4301 mags that have about a 100 hrs since o/h.

In flight only ; when operating on RIGHT or BOTH mags the runway lights are turned ON.They may be at different settings but always ON. The aircraft radio will not function to Transmit also. Flying LEFT only all is fine. Remove radio and issue continues.

All plugs leads test fine with a Lead Tester. We may swap mag positions to help diagnose . I don’t think a harness swap would work. A flight with p- leads disconnected may be in the works.

Other thoughts?
 
Last edited:
Magman said:
C-150 with Slick 4301 mags that have about a 100 hrs since o/h.

In flight only ; when operating on RIGHT or BOTH mags the runway lights are turned ON.They may be at different settings but always ON. The aircraft radio will not function to Transmit also. Flying LEFT only all is fine. Remove radio and issue continues.

All plugs leads test fine with a Lead Tester. We may swap mag positions to help diagnose . I don’t think a harness swap would work. A flight with p- leads disconnected may be in the works.

Other thoughts?
Click to expand...
How does a magneto turn on runway lights?
 
Magman said:
A flight with p- leads disconnected may be in the works.

Other thoughts?
Click to expand...
My thought is that's a bad thought. I think I'd be figuring out what's going on before I flew this thing.
 
Sounds like an expensive hangar remote control, you can probably label it as such and sell it too.
 
Sounds like some serious EMI. Maybe you could try cooking a hotdog with it.
Wonder if it would persist with the VHF antenna removed.

Nauga,
goodbye A&M
 
1721313934714.png

Perhaps @Dan Thomas will chime in here with an answer. He's pretty clever with odd things like these ...
 
To clarify, as it seems some are misunderstanding, or I'm misunderstanding them. He's not saying his mags are turning on the lights that are on the runway. he's saying they are turning on the light in his aircraft that aims at the runway.

I think.

*edit* No, I'm wrong. I totally misread it. Yes, it's aliens.
 
Ok, I've got to know. How the heck did you even figure all of that out that flying on left didn't cause it? What would ever posses a person to turn off a mag and see if runway lights turn on or not?

I'm looking at the calendar for April 1.
 
Salty said:
I'm going to go sit at his airport with a handheld and turn the lights on and off every time he's in the cockpit.
Click to expand...
Haha. But the handheld radio is a good idea. Someone listening on the ARCAL frequency while the airplane does its runway light thing would give some answers, as long as the radio operator knew enough about such stuff to interpret the noise.

The strange thing is that it continues to befuddle the lights with the Com right out of the airplane. This implies that the ignition is talking directly to the ARCAL, which in turn implies a massive broadband RF leak from the ignition.
 
Dan Thomas said:
Haha. But the handheld radio is a good idea. Someone listening on the ARCAL frequency while the airplane does its runway light thing would give some answers, as long as the radio operator knew enough about such stuff to interpret the noise.

The strange thing is that it continues to befuddle the lights with the Com right out of the airplane. This implies that the ignition is talking directly to the ARCAL, which in turn implies a massive broadband RF leak from the ignition.
Click to expand...

Could the P-lead be wired to one of the comm antennas? Just kidding of course ... sort of ...
 
It is very hard to imagine how a conventional magneto could output short bursts of around 122 MHz to activate the ARCAL receiver, especially since it is presumably in normal operating condition. I would be inclined to write this off as a troll or joke, but Magman's posts have been straightforward and helpful in the past...
 
Pretty slick magneto you have there.

Swap out the right mag and see if the issue persists.
 
Nobody likes to replace ignition harnesses these days because they are so terribly over priced. The lead tester will not test for a spark plug wire that has a pin prick hole in the insulation. Here's https://www.championaerospace.com/sales-support-usa-canada#SalesandTechnicalSupport recommendation:

Q. WHAT IS THE LIFE EXPECTANCY OF MY SLICK BY CHAMPION HARNESS?​

A. Champion recommends 15 years or engine TBO hours replacement interval.
Click to expand...

We use to turn the AWOS and Runway lights with the old WWII vintage spark plug tester. When the air pressure was cranked up to 100 psi the leaking spark tester wire could do all kinds of weird stuff around the airport like make the AM/FM radio crackle even when it was unplugged.

Don't rule out an Ignition Switch with a carbon track inside either.
 
flyingbrit said:
It is very hard to imagine how a conventional magneto could output short bursts of around 122 MHz to activate the ARCAL receiver, especially since it is presumably in normal operating condition. I would be inclined to write this off as a troll or joke, but Magman's posts have been straightforward and helpful in the past...
Click to expand...
I would suspect a problem with the ARCAL receiver. It is supposed to detect a discrete, highly accurate carrier frequency, in bursts of 3, 5 or 7 within five seconds (depending on J or K type), so it should not be easily fooled by ignition noise of any sort. It would be interesting to know if any other airplanes are affecting this field. And apparently, it only happens when the airplane is in flight, throwing another factor into the problem.

The airport runway lighting system is, if it's like the one I used to maintain, a long string of transformers, one buried under each light abut 20" down, all wired in series in a 600-volt circuit. Each transformer drops that voltage to 4.5 volts for the bulb, a low voltage to try to avoid big sparks that might set fire to spilled fuel in an airplane splatters itself on the runway and breaks a bulb.

That big loop of wire all the way around the runway and taxiway and ramp could act as a huge antenna, picking up RF and feeding it into the electrical supply near the ACAL receiver/decoder box. But, again, that receiver and its decoder would have to be pooched somehow.

Electronics can be tricky. We ran into a problem with the alternator going offline in flight, right after we took off. It turned out to be a leaky Com antenna connection in the ceiling of the airplane, where moisture had corroded the bayonet nut's grounding. When we made the (uncontrolled field) call for takeoff, Com RF radiated out and was picked up by the airplane's wiring, creating sharp little voltage spikes that the ACU (electronic alternator regulator and overvolt sensor assembly) would interpret as overvoltage, and the ACU would shut the regulator and therefore the alternator off. Those electronic doodads work on tiny currents compared to the old electromechanical regulators and 50-year-old overvolt sensors, which needed much more current so that escaping RF wasn't enough to bother them.
 
Klaus M said:
We use to turn the AWOS and Runway lights with the old WWII vintage spark plug tester. When the air pressure was cranked up to 100 psi the leaking spark tester wire could do all kinds of weird stuff around the airport like make the AM/FM radio crackle even when it was unplugged.

Don't rule out an Ignition Switch with a carbon track inside either.
Click to expand...
Best input so far.

That mag switch, in a C150, depending on the year of the airplane, is probably an ACS switch, and they are affected by an AD that demands removal, cleaning and inspection every 2000 hours. Cessna used a lot of those switches. The contacts in them can burn when the starter is engaged/disengaged, and I think (never got into the tiny details) that the starter contact plate is also the right mag plate when in Run position. The AD demands a diode across the starter contactor coil to prevent switch contact arcing.

One of the dumber things I dealt with was annual log entries stating that the Bendix ignition switch AD inspection was done, sometimes for 30 years in a row. That was to check to see if the engine would keep running if the switch was forced past Off a bit, where the affected switches would unground one mag. I would get under the instrument panel to see what switch was in it, and way too often it was an ACS switch, way out of AD compliance, just because every mechanic had assumed it must be a Bendix. While under the panel I would also often find other neglected stuff, some of it dangerous. Horribly shoddy inspections, those airplanes were getting.

https://drs.faa.gov/browse/excelExternalWindow/B8ABD56539B4684886256A3E00759DBF.0001
 
I vote faulty ignition switch to start. Not sure how it's providing power to the landing lights, unless the wires are shorted behind the panel.
 
Mikey52 said:
I vote faulty ignition switch to start. Not sure how it's providing power to the landing lights, unless the wires are shorted behind the panel.
Click to expand...
Magman said it was turning on the airport's runway lights, not the airplane's landing or taxi lights. Big difference.

The ignition switch's only connection to the aircraft's electrical system is in the start circuit. The magnetos are totally independent of the electrical system. That switch has nothing to do whatever with the airplane's landing lights.
 
First I’d like to thank Gary and Flyingbrit for their kind comments.

Second I’ll thank Dan and Klaus for the technical input.

Here’s the update after Mx Check Flights:

Note : Lights ON = radio bad Lights OFF = radio good

P- leads disconnected = No lights

Connect LEFT p-lead only = No lights

Connect RIGHT p-lead only = Lights

Next step will be to swap p-leads at mags if long enough.


/////;////////////////////////////;////////////////////////////(


The aircraft is a 1966 with pull start.

Slick has stated that the 4301 produces less EMI than the previous 4000
and 4200 Series.


The goal here is to diagnose the issue and not just replace parts.


I’ve been involved with many avionics installs but always with an avionics tech. Avionics troubleshooting is not my forte.

I have seen some strange problems:

Original Cessna ELT would pick up local AM 1520 and introduce it where it
would overwhelm Comm . Cure was putting in a Narco ELT.

Approach Certified UPS- GPS would not meet test parameters until the
ELT antenna was relocated extremely aft.

Avionics that malfunction can be discouraging and dangerous.
 
Magman said:
The goal here is to diagnose the issue and not just replace parts.
Click to expand...
Don't you have another available mag to swap in temporarily to rule out the right mag being the source of the issue? If the issue is resolved by a right mag swap, then the right mag was the cause.
 
If we had another 4301 I would consider doing the swap.However; we don’t. Swapping mags, harness or p- leads in place would be an alternative if they would reach.

Per #23 the problem seems to be with the p-lead/switch system. Klaus, Dan and Mikey may have nailed it. Shielding , carbon tracking in switch, maybe cracked p- lead insulation allowing arcing to shielding which then becomes an antenna? Input IS appreciated!

If the RIGHT mag is ON the runway lights will go on when about
1 mile from the airport.
 
Magman said:
If we had another 4301 I would consider doing the swap.However; we don’t. Swapping mags, harness or p- leads in place would be an alternative if they would reach.

Per #23 the problem seems to be with the p-lead/switch system. Klaus, Dan and Mikey may have nailed it. Shielding , carbon tracking in switch, maybe cracked p- lead insulation allowing arcing to shielding which then becomes an antenna? Input IS appreciated!

If the RIGHT mag is ON the runway lights will go on when about
1 mile from the airport.
Click to expand...

You might patent that to the airline guys that forget how to turn them on.
 
Magman said:
The aircraft is a 1966 with pull start.
Click to expand...
That means that any ACS switch in it is not affected by the AD. Only the switches with the Start function are affected.
nrpetersen said:
Bet that ground receiver for the runway light control has surplus sensitivity.
Click to expand...
They're adjustable. We turned the sensitivity down on ours. South/central Alberta has many uncontrolled rural fields with ARCAL lighting, all at the same frequency, and if some pilot fired the lights at one of them, the lights at others 25 miles away would come on. A lot of big electrical bills for no good reason. Someone told us that bored airline pilots would click the ARCAL frequency at night just to see the lightshow.
 
We’ll do a few more tests before replacing anything.

Not much left other than switch and p- leads.

I’m not wise in the ways of shielding which my belief is that if done wrong

will make things worse. Ground one or both ends on p-leads? I’ve seen ratty

with no issues.


Considering the year it is likely a Bendix switch. New is $$$ and Repair Kits

are rare. The ACS switch w/o “ Start” is not a PMA part and they say 337

for Certified aircraft. One option might be the ACS switch with Start and

not enable Starter feature. It’s only a few dollars more than Exp.

Would be set if you wanted to upgrade the Starter too.
 
Dan Thomas said:
That means that any ACS switch in it is not affected by the AD. Only the switches with the Start function are affected.
Click to expand...
If a switch with the start function is installed but the starter isn't connected to it, does the AD still apply?
 
IIRC a diode must be installed on the Starter Contactor and there is none

used with Pull Start .

Recurrent portion of of AD is at 2000 hr intervals so it’s not a major issue.
 
It's simply an odd coincidence. Somebody else is turning the runway lights ON, just happened to be they went OFF at the exact moment you switched to left mag. The universe is weird like that, happens all the time. Your radio is a different issue, not related whatsoever.
 
Once is a coincidence; twice a miracle.

It’s likely 70-80 times though.

Radio sent out twice and deemed fine.

It does work fine too; as long as the RIGHT mag is OFF..

It will get solved.
 
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