Wednesday, June 15, 2005


A Visit to the Transpondoctor

The Gremlin strikes!Yellowbird has always had a bit of an identity problem. Specifically, her transponder has been intermittently intermittent at least since I bought her. Even the pilot who delivered her had problems. At times it would read correctly, but sometimes ATC would report the mode C as being either dramatically off or missing altogether. I've had a few times where ATC reported an incorrect squawk code, and even once where they told me that they were picking up two different squawks, one digit apart. Like any good pilot, I assumed that if I ignored the problem, it would eventually go away. Gremlins really only want attention, and if they don't get it, they will usually move to someone else airplane. Unfortunately, my transponder gremlin decided that if I wasn't going to pay attention, it would appeal to a higher authority.

For the past month or so, Faithful Instructor George has been enduring my attempts to master the intricacies of instrument flying. The last two instrument lessons were filed as IFR so that we could do some approaches at KBAF. We had been with Bradley approach for only a few minutes on the first lesson last week when they asked us to confirm our altitude. We had been cleared to 4,000 feet, but had overshot by about 500 feet and was wandering up and down as I tried to get trimmed for level flight amongst the thermals of a warm humid afternoon. I sheepishly reported that I was returning to 4,000, but the tower replied that they had our mode C indicating 1,100.

The mode C issue of last week's lesson was only the beginning of troubles. We reset the transponder to no avail, and then turned off the mode C. From then on, ATC frequently asked us to confirm our squawk code, and finally asked us to change to a similar code of one digit's difference. We had both copied the same code when we got our clearance, so we wondered if maybe ground had given us the wrong code, but our next lesson was to dispel that suspicion.

This time, Bradley immediately started to question our squawk. They didn't report any mode C issues, but they told us that they were getting multiple hits off our transponder, with different codes, and that we were setting off all sorts of alarms in their system. We had planned on three approaches, and while vectoring us for the third, they got sufficiently fed up to tell us to make it a full stop and don't come back up until we got the transponder fixed. We were going for a full stop anyway, so we landed and concluded the lesson.

Yellowbird has been to Worcester to see the transpondoctor twice in the last 12 months to have this issue looked at, and both times, the transponder and its fittings checked out perfectly on the ground. Still, he cleaned the connections and re-racked the transponder just to make sure that it wasn't a case of dusty electrical connections. If that didn't clear things up, his next trick would be to temporarily replace the transponder with a fresh unit of the same model. After being scolded out of the sky by the Bradley controller, we didn't have a choice.

In the examining roomYesterday Yellowbird and I braved the bumpy skies for the short trip over to Worcester for a third visit. The afternoon thunderstorms had moved east, leaving low ceilings and plenty of turbulence, but we still had decent VFR conditions. At Worcester, the transpondectomy involved nothing more complicated than sliding the old unit out of its rack and sliding a replacement in to take its place. I'll fly for a few weeks with the replacement. If I still have problems, we'll know to look for another solution. If not, then Yellowbird will be getting a new transponder.

We went up for another instrument lesson this evening. We had no apparent problems with the transponder's squawk, but the mode C, which checked out fine on the way back from Worcester, was now reading about 1,000 ft low. The weather is supposed to be nicely IFR for a few days, so I may not get the chance to have this checked out for a while. Dang. At least I got in 20 minutes of actual, as well as my first ILS approach in IMC.


Posted by Anonymous Anonymous at 11:09 PM, June 16, 2005  

I didn't see an email address on here, or I would have emailed this. Do you by any chance have an Atom feed of your site available? I believe that Blogger provides these, though I'm not sure if they are on by default. If you do, could you please send the information to: ?

Thank you,

Posted by Blogger Yellowbird at 9:50 AM, June 17, 2005  


I just added a link to the Atom feed below the archive list. I'll probably play around with this to see if I can come up with a better presentation, but for now, the link is there.

Many thanks for the suggestion!

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