Narrative:

While flying back from trenton-robbinsville (N87) on an ADIZ flight plan, I squawked 1200 inside the ADIZ. I had entered the dc ADIZ with an assigned squawk code and was communicating with potomac approach. With my destination, annapolis (anp), in sight, I informed potomac approach that I had the airport in sight as instructed. The usual communication from potomac is 'radar service terminated, frequency change approved, keep the squawk until on the ground.' I am not sure they made this radio call as above. I repeated this flight on sunday, and ATC did not say the part about keeping the squawk. I knew it was procedure to keep the squawk code. I can't recall exactly what happened but it may have been one of two things. 1) I changed the squawk without thinking, or 2) accidentally changed the squawk by bumping the transponder while changing frequencys. Either of these is easily done, as the transponder is a single button to push that changes the squawk code to 1200 (VFR). If the transponder had been of the type that requires twisting 4 knobs to set each digit of the code, I am sure this mistake would not have happened for either reason. After I landed and shut down the plane. At the tie-down spot, an airport employee approached me and informed me that potomac approach had called the airport and wanted me to call them. I called the number and, after getting my personal information, they informed me that I had changed squawk codes within the dc ADIZ and would be receiving a pilot deviation. After finishing the call, I turned on the transponder and saw that 1200 was the last code entered, although I did not remember putting it in. I have flown in and out of the dc area ADIZ on several occasions and I am aware of the correct procedures.

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Original NASA ASRS Text

Title: P-28A PLT RPTED THAT HE VIOLATED THE DC ADIZ.

Narrative: WHILE FLYING BACK FROM TRENTON-ROBBINSVILLE (N87) ON AN ADIZ FLT PLAN, I SQUAWKED 1200 INSIDE THE ADIZ. I HAD ENTERED THE DC ADIZ WITH AN ASSIGNED SQUAWK CODE AND WAS COMMUNICATING WITH POTOMAC APCH. WITH MY DEST, ANNAPOLIS (ANP), IN SIGHT, I INFORMED POTOMAC APCH THAT I HAD THE ARPT IN SIGHT AS INSTRUCTED. THE USUAL COMMUNICATION FROM POTOMAC IS 'RADAR SVC TERMINATED, FREQ CHANGE APPROVED, KEEP THE SQUAWK UNTIL ON THE GND.' I AM NOT SURE THEY MADE THIS RADIO CALL AS ABOVE. I REPEATED THIS FLT ON SUNDAY, AND ATC DID NOT SAY THE PART ABOUT KEEPING THE SQUAWK. I KNEW IT WAS PROC TO KEEP THE SQUAWK CODE. I CAN'T RECALL EXACTLY WHAT HAPPENED BUT IT MAY HAVE BEEN ONE OF TWO THINGS. 1) I CHANGED THE SQUAWK WITHOUT THINKING, OR 2) ACCIDENTALLY CHANGED THE SQUAWK BY BUMPING THE XPONDER WHILE CHANGING FREQS. EITHER OF THESE IS EASILY DONE, AS THE XPONDER IS A SINGLE BUTTON TO PUSH THAT CHANGES THE SQUAWK CODE TO 1200 (VFR). IF THE XPONDER HAD BEEN OF THE TYPE THAT REQUIRES TWISTING 4 KNOBS TO SET EACH DIGIT OF THE CODE, I AM SURE THIS MISTAKE WOULD NOT HAVE HAPPENED FOR EITHER REASON. AFTER I LANDED AND SHUT DOWN THE PLANE. AT THE TIE-DOWN SPOT, AN ARPT EMPLOYEE APCHED ME AND INFORMED ME THAT POTOMAC APCH HAD CALLED THE ARPT AND WANTED ME TO CALL THEM. I CALLED THE NUMBER AND, AFTER GETTING MY PERSONAL INFO, THEY INFORMED ME THAT I HAD CHANGED SQUAWK CODES WITHIN THE DC ADIZ AND WOULD BE RECEIVING A PLT DEV. AFTER FINISHING THE CALL, I TURNED ON THE XPONDER AND SAW THAT 1200 WAS THE LAST CODE ENTERED, ALTHOUGH I DID NOT REMEMBER PUTTING IT IN. I HAVE FLOWN IN AND OUT OF THE DC AREA ADIZ ON SEVERAL OCCASIONS AND I AM AWARE OF THE CORRECT PROCS.

Data retrieved from NASA's ASRS site as of July 2007 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.