C172 PLT; THROUGH HABIT PATTERN; HIT THE BUTTON THAT CHANGED THE XPONDER CODE TO VFR; 1200.

Narrative

APCHING THE DC ADIZ FROM THE N; I OBTAINED A XPONDER CODE AND CLRNC INTO THE ADIZ. JUST PRIOR TO ENTERING THE ADIZ SOME 15 TO 20 MINS LATER; I ASKED ATC TO CONFIRM MY ADIZ CLRNC. ATC SAID THAT CLRNC HAD ALREADY BEEN GIVEN BEFORE. ATC ALSO ADVISED THAT FREQUENCY CHANGE WAS APPROVED AND THAT I SHOULD MAINTAIN MY SQUAWK CODE UNTIL ON THE GND AT GAITHERSBURG. I REPEATED THE INSTRUCTIONS AND CHANGED FREQUENCY. BY FORCE OF HABIT; I ALSO PUSHED THE VFR BUTTON ON MY XPONDER AND STARTED SQUAWKING 1200 IN THE ADIZ. AFTER ANNOUNCING MY POS ON THE CTAF; I REALIZED MY MISTAKE AND IMMEDIATELY RESTORED THE ASSIGNED SQUAWK CODE. I THEN RETURNED TO THE BWI APCH FREQUENCY AND EXPLAINED MY ERROR. THE CTLR REMINDED ME THAT I WAS TO REMAIN ON THE SQUAWK CODE UNTIL ON THE GND. I REPEATED THE INSTRUCTION AND APOLOGIZED. THE CTLR SAID; 'NO PROBLEM.' THIS ERROR WAS CAUSED PURELY BY HABIT. CTLRS ARE CONSTANTLY TELLING YOU 'FREQUENCY CHANGE APPROVED; SQUAWK VFR.' I WAS NOT TOLD TO SQUAWK VFR IN THIS CASE; BUT I DID ANYWAY BECAUSE THAT'S WHAT I ALWAYS DO; OR DID BEFORE THE ADIZ. ALSO; I DID NOT EXPECT TO BE TOLD TO CHANGE FREQUENCY WHEN I ASKED FOR CONFIRMATION OF MY ADIZ CLRNC. THIS CAUGHT ME SLIGHTLY OFF GUARD. IT WAS CLR TO ME THAT THIS CTLR DID NOT WANT TO BE DEALING WITH ME SO I TRIED AS QUICKLY AS I COULD TO REPEAT HIS INSTRUCTIONS AND PROCEED TO THE CTAF. THAT HASTE ON MY PART ALSO CONTRIBUTED TO MY MISTAKE. I HOPE THAT MY QUICK RECOGNITION OF THIS MISTAKE AND MY CORRECTION OF IT HELPED TO LIMIT THE TROUBLE I CAUSED.