MIF stuck ptt + solution

[GeorgeC]

When picking up my plane from its annual yesterday, I flipped my avionics breaker on, and my gtr 225 helpfully informed me "stuck pilot ptt". Power cycle a few times, monkey with switch/wiring a bit, no joy.

Called over for a mx grownup's help. We looked under the panel and didn't find anything obvious. Shot some contact cleaner in the switch, still no joy. I was about ready to remove the ptt switch and cut the wires (I had a portable ptt) when the mx stayed my hand; she had an idea.

Apparently the lugs on the headset jacks stick out radially and are not insulated or heatshrunk or anything. They had removed part of the panel while troubleshooting another squawk, so, the hypothesis was that the jacks had been reinstalled in a different orientation than before, and were shorting to ground on a bracket or tray or something.

A half inch socket and a few minutes of fiddling later and I was good to go.

 

[Let'sgoflying!]

Had an airplane where if you installed the interior panel screws without consideration to where they came from, the long screws would contact the receptacle internals.
Needed the short screw in that location.

 

[asicer]

Had an airplane where if you installed the interior panel screws without consideration to where they came from, the long screws would contact the receptacle internals.
Needed the short screw in that location.

You couldn't use short screws all around? How about a different color for the short screw?

 

[Timbeck2]

Sounds like the phenolic washers weren’t reinstalled properly

 

[Gary Ward]

I spent quite a bit of time and a little money buying/putting all the right screws in the right places in my in interior plastics since I am the guy to remove them for annuals inspections. I am particular about where the screws go.
Now when I take it to the avionic shop I remove the interior before taking over. They love that and have told me so. They start working on it right away and I get it back fast because they appreciate that I do the interior disassembly and re assembly. Don't F with my screws! lol

 

[Dan Thomas]

We had a Cessna come in whose aileron controls were stiff. Someone had put a long screw into the plastic doorpost cover on the aft doorpost, and that screw had run up against the aileron pulley at the bottom of that post and jammed it. The cable was dragging over the pulley. Lots of friction.



I found at least one too-long screw gouging into the 1/2" aluminum fuel line running down inside that same doorpost. That could get real serious. Fuel running into the cabin.

The old 172s (and some others) didn't have the quick-release Southco fasteners in the cowling, between the top and bottom cowls. They used sheet-metal screws in the top cowl that ran into Tinnerman nuts in the bottom cowl. The screws were necessarily short. I found one that was up against a rocker cover, and engine vibration was trying to chew a hole in the cover. Didn't do the cowling any good, either, with the engine shaking it. Someone here on POA, I think it was, actually had an oil leak showing along the cowl, and that screw had poked right through the rocker cover. The vibration had made the hole pretty big and oil was getting out. Didn't do that cowling any good, either.

Some guys are afraid that screws will back out, so they overtighten everything. That means that the hole in the metal is torn out, and the next guy puts a larger screw in. That one gets torn out, so now we're up to a #12 screw and a huge hole. Next step would be a 1/4" lag wood screw. It's crazy.

Or the tinnerman nut is busted due to overtightening and now it's either remove the old nut and install a new nut, or just use a bigger screw. Guess what most mechanics do...

 

[GeorgeC]

@Dan Thomas, speaking of sheet metal screws and Tinnerman nuts... When are you supposed to use type A vs. type B? I've found a mixture of both. I assume the correct answer is not "if one doesn't fit, try the other"...

Bonus: Some have nylon washers, others don't.

Type A:

Type B: