Transponder Challenges

It was a lovely day in Southern BC, and I so did some circuits for a while. Halfway through something funny occurred. Tower asked me to reset my transponder, advising that I'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).

I recycled it like they requested, and asked them if it was working. It was gone. The tower told me to get it looked at once I was down.

Good thing for me, one of my partners is an avionics guy. What I thought was going to be a hassle turned into something fun.

The first step is taking the transponder out. 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? An Allan key fits right inside that little hole.

You stick in the Allan key, and that unscrews a long retaining screw that attaches the transponder to the back of the instrument panel. You can see how nicely it slides out. Not at all like my ’72 Toyota Celica.

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

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. It was easy as can be. We cleaned the connector with alcohol and re-installed it. I powered it up, waited a minutefor the tube inside to warm up, but no go!

Of course, there was something simple I should have checked in the first place, possibly while in the air – the fuse. I pulled it, inspected it and found nothing wrong. I replaced it and you know it, the transponder light blinked blue. Good to go!

What caused it?

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 caused my own dilemma. Brushing my fingers across the fuses must have been the cause. I won’t do that twice, and if I have another non-critical electrical malfunction I’ll be sure to check the fuses right away.
Live and learn….

By: Rob Chipman

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Rob Chipman maintains several blogs, including Bush Pilot in Training, and Bush Pilot Properties