ATC / Transponder Question

[JGoodish]

While I am still attempting to evaluate my encoder issue, I requested an altitude check from the local TRACON shortly after departure. Mode C was actually within 100 feet, but the controller complained that he was seeing two secondary returns in my location, same position, same altitude, and same direction of flight. It became apparent that my aircraft was likely responsible for both returns, even though i only have a single transponder.

Does anyone know what could cause this type of problem?


Thanks,
JKG

 

[denverpilot]

Transponder replying twice to interrogation. Very broken.

 

[JGoodish]

Transponder replying twice to interrogation. Very broken.

That's what I assumed, but why? And are there any other potential causes?

In my case, if it's doing this, it's intermittent. This is the first time that I've had such a report.

With this and the encoder issue, I'm really wondering what the heck my avionics shop did when they did the biennial altimeter/transponder test earlier this month. They supposedly checked the transponder and encoder twice in the aircraft, and everything was fine. They pulled the encoder to the bench, and it was fine there. But I fly the airplane and I have problems. Of course, I get billed for all of this test time at the avionics shop for equipment that still appears to be broken, but... they're the only game in town.


JKG

 

[roncachamp]

While I am still attempting to evaluate my encoder issue, I requested an altitude check from the local TRACON shortly after departure. Mode C was actually within 100 feet, but the controller complained that he was seeing two secondary returns in my location, same position, same altitude, and same direction of flight. It became apparent that my aircraft was likely responsible for both returns, even though i only have a single transponder.

Does anyone know what could cause this type of problem?

It could be caused by the TRACON. If the code block you were using is selected by a backup system that the controller didn't know was selected it could produce the effect you describe. Before doing anything expensive check it on another flight. If it happens again ask for a different code block, try it with a different TRACON if you can.

 

[JGoodish]

Thanks guys. I will have to do some additional evaluation to determine whether I am able to observe a repeat occurrence.


JKG