Winding if there is a software readout of the transponder serial number somewhere in the setup dialogues. I need it for registration and it’s going to be two hours work to get at it under the seat to read the label. Yes, I should have recorded it. 
Sadly, I’ve lost that box. The S/n may be on the invoice, otherwise it’s get out the spanner. I’ve already checked my build log. Yes, registration people here want serials, model numbers of everything![]()
you need it when you do 91.413 IFR transponder check----if it isn't in software (don't think it is), it should be----kind of tough of IFR guy if he doesn't have it when filling out paperwork
The first time I had mine checked, during Phase I, they asked for it and I didn't have it. Went dumpster diving behind the baggage compartment to pull the transponder to read the serial, and the tech had a sharpie in his hand already - wrote it on top where it can be seen without having to do the dive. Now why didn't I think of that?It's not in the menus, and I've had four or five XPDR checks done since finishing the plane 8 years ago, and we never pulled the baggage bulkhead to get back in and look at the serial number. I *have* it, as I have a list of every serialized item on the entire airplane, but I don't recall the technician ever asking for this info.