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.