The hidden world of aircraft wiring

[Bob Weber]

I've started this one in an attempt to bring more awareness and understanding about arguably the most critical component of an aircraft. Your wiring.

Also to minimize my hijack of another thread.

This was a project I took on earlier this year, an autotrim issue causing a pretty good porpoise on autopilot.

During a ground check over the phone, we detected and located this in less than an hour.

My client was aware of the symptom, but had not recognized the severity of the situation.

In this case the avionics would intermittently not power up when the avionics master breaker switch was flipped on.

I told him we needed to begin there, I preach a simple rule, when you see a bug, stomp on it.

Here is the bug we found, I hope to have everyone show a picture of the wiring maladies they have spent time and money on.

Once we stomped on this bug, his autopilot problem was gone..

 

[kris_adams]

Hey Bob.  I see a lot of wiring zip tied.  What's the worst offense we are seeing?  Looks better than the back of some panels I've seen.  (just a private pilot...no wiring expertise claimed at all).  -KA

[Bob Weber]

Just now, Kris_Adams said:

Hey Bob.  I see a lot of wiring zip tied.  What's the worst offense we are seeing?  Looks better than the back of some panels I've seen.  (just a private pilot...no wiring expertise claimed at all).  -KA

Just above and to the left of that big black tyrap is a loose ring terminal carrying the power to the avionics buss, or sort of carrying the power.

Notice the discolored terminal and wire?

[rbridges]

I may be missing the obvious, but is that beige wire in the center of the pic connected properly?

[Oldguy]

6 minutes ago, Kris_Adams said:

Hey Bob.  I see a lot of wiring zip tied.  What's the worst offense we are seeing?  Looks better than the back of some panels I've seen.  (just a private pilot...no wiring expertise claimed at all).  -KA

 

1 minute ago, rbridges said:

I may be missing the obvious, but is that beige wire in the center of the pic connected properly?

I think this is what he is referring to as a problem.

 

[rbridges]

1 minute ago, Oldguy said:

 

I think this is what he is referring to as a problem.

 

yeah, that's the beige wire I was mentioning.

[Bob Weber]

11 minutes ago, rbridges said:

I may be missing the obvious, but is that beige wire in the center of the pic connected properly?

Funny you should notice the color, It has been baking for a while due to a loose connection. You are not missing anything, good eye!

We need to be watching for all forms of these issues with older aircraft.

[Bob Weber]

11 minutes ago, rbridges said:

yeah, that's the beige wire I was mentioning.

The last 3 or 4 inches of that wire got hot enough to anneal the copper as well as the terminal end, the breaker components, and even the terminal on the other connected wire.

I recommended they replace all of it.

 

[Bob Weber]

Who can spot the missing screw? Much of what is in this area will not react very well to a loose screw...

[afward]

The screw is in that picture?!  Wow...  I'm not seeing it, though.

[Skates97]

This is not behind the panel, but is the wire going to the coffee grinder beacon. After it died (still lit up but the motor burnt out) I found this connection back in the empennage, it was wrapped in electrical tape.

 

[KSMooniac]

Thanks sharing stuff like this, Bob!

Don Maxwell has a nice collection of maladies that he shares at Mooney events from time to time that are frightening. Sharing this stuff is a great educational tool for all of us.

Sent from my LG-US996 using Tapatalk

[Bob Weber]

4 minutes ago, Skates97 said:

This is not behind the panel, but is the wire going to the coffee grinder beacon. After it died (still lit up but the motor burnt out) I found this connection back in the empennage, it was wrapped in electrical tape.

 

Welcome to the Hall of Flame! I would wager that connection contributed, at least in a small part, to the demise of the motor.

A loose connection drops voltage just as a resistor, a motor draws more current when ran on lower voltage.

The bright side here is an LED replacement!(no pun intended)

 

 

 

 

 

 

[Volzalum]

56 minutes ago, Bob Weber said:

Who can spot the missing screw? Much of what is in this area will not react very well to a loose screw...

Is it just behind the terminal insulation (against the box) on the white wire adjacent to the beige wire that is loose?

[Bob Weber]

11 minutes ago, Volzalum said:

Is it just behind the terminal insulation (against the box) on the white wire adjacent to the beige wire that is loose?

Good Eye!

It took several pictures before I was able to spot it, that can be a pretty overwhelming area to inspect and make sense of.

I was able to help my Client spot it, from 9,200 miles away!

Look at the insulator on the terminal of the white wire, it is discolored from heat as well.

 

[steingar]

I'm just glad there are experienced professional people to look at these things.  Were it left up to me I think the wiring could easily catch fire before I'd notice anything amiss.

[Bob Weber]

20 hours ago, steingar said:

I'm just glad there are experienced professional people to look at these things.  Were it left up to me I think the wiring could easily catch fire before I'd notice anything amiss.

Imagine the cost of that if you just started sending boxes out for repair.

We were able to find this problem and correct it with minimal time and materials.

 

Edited November 22, 2019 by Bob Weber
grammar

[Yetti]

I saw three things.  The loose ring terminal thing.  The routing on the red capped crimps.   I hoping those are crimps and not wire nuts.  and some tywrap routing and such.

 

 

The bottom photo is how the com relay was "fixed".  The electrical tape had mostly fallen off.

 

Edited November 25, 2019 by Yetti

[Bob Weber]

The terminal and screw on that 15 amp breaker looks discolored as though it had gotten hot.

Was it the one that was loose?