Transponder Breakdown

It was a great day in Southern BC, and we did circuits. Halfway through something occurred. The tower controller directed me to recycle the transponder, saying that we’d stopped showing up. (This isn’t as bad as it seems, because I was still on radar – they had me on radar, so they were only missing my altitude, and since I was in the circuit they knew what that was). Anyway, I checked it and tested it and it was kaput. Tower asked that I get it looked into once I landed.

Fortunately, one of my partners repairs avionics. What I thought was going to be a big production actually turned out to be super easy.

It starts with is pulling the transponder. If you’re only experience is installing car stereos, a NARCO AT 150 is a treat.

The transponder is the unit at the bottom, and you’ll see there is a little hole on the bottom right of it right under the IDENT button. Guess what? There’s an Allan key in there.

It loosens a long screw that attaches the instrument to the plane. You can see how nicely it slides out. Not at all like my ’72 Toyota Celica with the AM/FM 8 track.

You can see the attachment point at the end of the mounting box, along with the connector.

No wire harness or plug. Instead, it connects just like a card in a computer.

Once it was out we threw it on a few testers. Surprise, surprise, it worked fine. We cleaned the connector with alcohol and re-installed it. I powered it up, waited a bit for the tube inside to warm up, but no good!

Of course, there’s an obvious thing I should have thought of in the first place, possibly while in the air – the fuse. I pulled it, inspected it and found nothing wrong. I replaced it and as I suspected, the transponder light blinked blue. Good to go!

What happened? Gremlins?

Of course not. Remember, I was flying circuits on my way to soloing. Take off, turn out, do the downwind check “Primer in and locked, masters on, mags both, fuses and circuit breakers in….”

And that’s when I screwed my own pooch. Running my fingers over the fuses must have been the cause. I won’t do that again, and if I have another non-critical electrical failure I’ll be sure to check the fuses right away.