Wiring issue?

[Michael Rath]

My cousin was flying my Comanche today and when he was on approach he turned on both wing mounted landing lights. Thirty seconds later he noticed a burning wire smell and a little smoke comming from under the breaker panel. He immediately turned off the lights and the smoke stopped. No breakers were popped. He landed, smoke and smell dissipated and had no more issues.


Obviously the airplane is grounded! I am out of town until Monday so not sure how bad it is. I am pretty sure it is related to the landing lights.


Anyone heard of this issue with the landing lights before? Bad wiring? Bad breakers? I will get with my A&P on Monday but any advice on where to start would be appreciated.

Thanks

Michael

[Zach Grant L1011jock]

Yep, all of the above....Lost my entire electrical system in a similar way, night, localizer app. to minimums....needless to say, the next day I started rewiring the entire airplane, including new more sensible circuits and all new klixon breakers in the panel so you can actually see what is going on, instead of trusing circuit breaker brail....
-Zach

[Michael Rath]

Zach,

Just curious, how big of job was that, 20 hours, 40? Did you move all the breakers to the right side of the panel?

[Zach Grant L1011jock]

It was a big job (hrs didn't get counted...)! Yes I mounted all of the new breakers on the right side of the panel. I basically started with cutting EVERYTHING out of the airplane, and starting over, how I thought it should be done. I now have almost 50 breakers, honest to God main, essential and avionics buses, and all new wiring throughout. An interesting note, when I tested the old breakers, only 2 passed the mil spec test criteria. I really don't need to tell you, that is not a great deal when combined with faulty wiring!

[Michael Rath]

Wow! Any chance of you posting a picture of your breaker layout? I would like to see how it looks.

Do the switches also go bad or is it mostly the wiring and the breakers?

[Zach Grant L1011jock]

Yes switches go bad too. I installed all new switches as well, including 4 zone solid state dimmers for lighting.
-Zach

[JIMICS2452]

How did you document the changes? Log book entry or 337? Did you include schematics in the flight manual or maintenance records for future reference? I am about hto to a similar job.

Jim Hiatt

[Zach Grant L1011jock]

The answer to your question is yes. Some parts of the job are under the panel mod 337, some is a logbook entry and any substantive change has an amended schematic attached to it or notes ammending the drawing as in the case of splitting the fuel pump from the nav light circuit and installing a breaker for each. I didnt add schematics that did not exist originally in the flight manual or in the mx manual. As far as the changes that are not substantially different than original such as using a solid bus bar as opposed to daisy chaining the breakers, they are simply minor deviations and not documented as their function and their purpose are the same as original design.
Zach

[Michael Rath]

I got back to town today and had a chance to look at the breaker panel. I had a bad breaker that caused a short.

MR

[Zach Grant L1011jock]

Mike, check out viewtopic.php?f=93&t=4939 for pictures of my panel previously posted here. The breakers are visible on the right side, somewhat obscured by the yoke.
-Zach

[md11flyer]

Michael, Yes thats how it is supposed to be wired. The circuit breaker from the Alternator feed wire to the circuit breaker panel bus bar is supposed to protect the alternator and wire from to much current flow. In your case the main circuit breaker did not do its job when the amperage exceeded the feed wire capacity.
There are several reasons this could happen, Bad connection from the feed wire to the circuit breaker. ( example if a few strands of the feed wire were broken or not properly crimped at the connector the connector would overheat at the breaker breaker when a high load was placed on it, effectively the wire is a smaller capacity wire at the point of broken strands.
Or simply a loose fastener screw holding the wire to the circuit breaker.
Another, less likely reason is the aircraft was upgraded to a higher amperage alternator and main feed circuit breaker, but the feed wire was not upgraded to a higher capacity wire. If this is the case then you must either change the circuit breaker back the original amp breaker or upgrade the wire.
But that does mot address the main problem you have and that is the excessive current draw from your landing light(s).
You can test this out yourself in the hangar. First manually exercise the landing light circuit breakers to make sure they are not melted internally from a short. Then with battery master on and all other electrics off, switch one light on at a time and take note of the the amp gauge if the gauge shows less than 10 amps per light then your light circuits are fine. If the gauge jumps full discharge quickly turn off switch and master switch as you have now found your problem circuit.
If this is the case your landing light circuit breaker must be replaced and the cause of the short traced down.
I really can't see any other reason for the landing lights putting your electrical load so high as to cause melting of a main feed line. Except if you had the pitot heat on, the radar on, gear going down, flaps going down and if you have the really old narco tube radios.... then maybe.
Good luck, and let us know what you find
BTW , I might be wrong, but your A&P can fix your electrical wiring you don't need an avionics shop.

[JIMICS2452]

Thanks for the reply, Zach. I thought that it might be a multiple path installation, with the C.B. panel move covered under the new panel 337 and minor circuit changes
documented with a log book entry.

Jim

[Michael Rath]

Nice panel Zach!!

Below is a picture of the melt down.

md11flyer,

Thanks for the great hints. I will check those landing lights. I was planning on replacing the landing lights with LED lights and now is a good time to do it. I think it was a corroded wire from the alternator but those lights will get a good check out.

Thanks for all the input and I will keep you updated on my progress.

MR

[Kristin Winter]

It looks like the ring terminal may have been too large for the circuit breaker connection.

An A&P can do the repairs, the problem is that most do not have the terminals for heavy gauge wire, nor the crimping tool to crimp them. I am not close to SD, but I can fabricate heavier gauge wire with terminals if your local A&P isn't so equipped. I redid my electric panel last year and the stuff came in handy.

[Michael Rath]

That hole in the terminal did not start out that size. It melted out to that size! The rest of it is welded around the screw on the breaker!!

Michael