The International Cessna^® 170 Association

I'm getting ready to install the headset and mic jacks for my new radio and noticed something different about the mic jacks. They have a little "tang" on them that doesn't allow the step washer to sit flat. I know the jacks need to be insulated from the airframe using the washers. Am I missing something simple here?

I believe the "tang" is designed to fit into a hole in the mounting panel to keep the jack from turning. My suggestion is to cut or grind it off. See what others suggest before doing so.

I figured the tab was for some kind of index so it doesn't turn when mounted. I think I will just need to file it off.

The body of the jack has to be earthed and thus through the airframe and the tang stops rotation when being tighten by the the nut.

The jacks I put in 81D had an insulating washer on both sides as well as a thin collar to completely isolate the jack from the airframe.
Ground was managed via the intercom. This was to eliminate any outside noise.

The jack you show isn't doing that. it's simply grounding to the airframe and the tank is to keep it from rotating in the hole.
I'd file a slot in the hole and make use of the tang.

The jacks need to be isolated from the airframe by using the insulated washers. The com and mic is grounded via a wire to the audio panel. I think I must have ordered the wrong jacks. Letting the jack touch the panel would create a ground loop. I'll either file it down or get the right jacks.

It might allow generator or magneto noise to be introduced into the audio system.
Not really a ground loop but, that's another topic.

If your audio panel/intercom calls for the jacks to be isolated from aircraft ground then, yes you need to either file of the tab or get new jacks.
I just assumed those were the jacks that came with the the intercom.

Do you have the right isolation washers? They should have a very pronounced shoulder and require bigger holes in the panel to mount. There should also be one of these washers on BOTH sides of the panel to completely isolate the jack.

I also found it helpful to use a multi meter to check for a short (washer slipped) after tightening everything down.

I think Page 2 of the Sigtronics manual addresses these issues:
https://www.sigtronics.com/_pdf/air_pdf ... S_INST.pdf