Narrative:

I was departing our tower controled field; squawking our discrete code of XXXX. This is used only by aircraft wishing to depart (to the north or southeast) VFR. We do this several times a day. On this occasion I was following another company malibu which had just taken off ahead of me; and as I was climbing through about 1200 ft MSL; the mtn tower inquires if I had my transponder on. I advised yes and they said they did not see me; on their 'scope.' (this tower has a BRITE screen that feeds off of potomac's radar.) then they advised that they were not sure if it was my aircraft or the company malibu ahead. I reiterated that my transponder was on XXXX and that I was showing normal (with the response indicator clearly operating). They advised that they would call potomac landline and 'see what they say.' after about 30 seconds; the tower said '(call sign) they don't have you either.' then at this point the malibu ahead calls tower and says; 'I've had him on my traffic display (a transponder-based 'skywatch' system) since he took off.' I then switched to my other transponder and the tower says 'still negative.' I advised I could talk to potomac approach myself; as I was outside of class D at this point. Tower advised 'frequency change approved.' note: I was in communication with the other company malibu on our company frequency the entire time; and that pilot confirmed he saw my transponder target and altitude the entire time. I called potomac and the controller seemed to not know of any problem. I briefly explained that mtn tower's screen did not show my target. (I was still in the ADIZ; but nearing the exit point at that time). The controller had me go to a different squawk code (similar to 'yyxx' or something) and verified it was working and he 'idented' me. Then he had me switch back to XXXX code again; and verified he had me on that code! Seconds later; I exited the ADIZ; he had me switch to an xxzz code; said 'I wouldn't be concerned; there shouldn't be any problem; it's working.' then said 'frequency change approved.'

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Original NASA ASRS Text

Title: PA46 PLT IS ALERTED BY ATC TO POSSIBLE XPONDER PROBS AFTER DEPARTING MTN; INSIDE THE DC ADIZ.

Narrative: I WAS DEPARTING OUR TWR CTLED FIELD; SQUAWKING OUR DISCRETE CODE OF XXXX. THIS IS USED ONLY BY ACFT WISHING TO DEPART (TO THE N OR SE) VFR. WE DO THIS SEVERAL TIMES A DAY. ON THIS OCCASION I WAS FOLLOWING ANOTHER COMPANY MALIBU WHICH HAD JUST TAKEN OFF AHEAD OF ME; AND AS I WAS CLBING THROUGH ABOUT 1200 FT MSL; THE MTN TWR INQUIRES IF I HAD MY XPONDER ON. I ADVISED YES AND THEY SAID THEY DID NOT SEE ME; ON THEIR 'SCOPE.' (THIS TWR HAS A BRITE SCREEN THAT FEEDS OFF OF POTOMAC'S RADAR.) THEN THEY ADVISED THAT THEY WERE NOT SURE IF IT WAS MY ACFT OR THE COMPANY MALIBU AHEAD. I REITERATED THAT MY XPONDER WAS ON XXXX AND THAT I WAS SHOWING NORMAL (WITH THE RESPONSE INDICATOR CLRLY OPERATING). THEY ADVISED THAT THEY WOULD CALL POTOMAC LANDLINE AND 'SEE WHAT THEY SAY.' AFTER ABOUT 30 SECONDS; THE TWR SAID '(CALL SIGN) THEY DON'T HAVE YOU EITHER.' THEN AT THIS POINT THE MALIBU AHEAD CALLS TOWER AND SAYS; 'I'VE HAD HIM ON MY TFC DISPLAY (A XPONDER-BASED 'SKYWATCH' SYS) SINCE HE TOOK OFF.' I THEN SWITCHED TO MY OTHER XPONDER AND THE TWR SAYS 'STILL NEGATIVE.' I ADVISED I COULD TALK TO POTOMAC APCH MYSELF; AS I WAS OUTSIDE OF CLASS D AT THIS POINT. TWR ADVISED 'FREQ CHANGE APPROVED.' NOTE: I WAS IN COM WITH THE OTHER COMPANY MALIBU ON OUR COMPANY FREQ THE ENTIRE TIME; AND THAT PLT CONFIRMED HE SAW MY XPONDER TARGET AND ALT THE ENTIRE TIME. I CALLED POTOMAC AND THE CTLR SEEMED TO NOT KNOW OF ANY PROB. I BRIEFLY EXPLAINED THAT MTN TWR'S SCREEN DID NOT SHOW MY TARGET. (I WAS STILL IN THE ADIZ; BUT NEARING THE EXIT POINT AT THAT TIME). THE CTLR HAD ME GO TO A DIFFERENT SQUAWK CODE (SIMILAR TO 'YYXX' OR SOMETHING) AND VERIFIED IT WAS WORKING AND HE 'IDENTED' ME. THEN HE HAD ME SWITCH BACK TO XXXX CODE AGAIN; AND VERIFIED HE HAD ME ON THAT CODE! SECONDS LATER; I EXITED THE ADIZ; HE HAD ME SWITCH TO AN XXZZ CODE; SAID 'I WOULDN'T BE CONCERNED; THERE SHOULDN'T BE ANY PROB; IT'S WORKING.' THEN SAID 'FREQ CHANGE APPROVED.'

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.