M20P PLT ENTERED DC ADIZ WITHOUT CLRNC OR A DISCRETE XPONDER CODE.

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I WAS RETURNING FROM MIV TO EZF VFR. I HAVE A GPS IN MY PLANE WITH CURRENT CARD AND BEING LCL AM VERY CAREFUL WITH ALL OF THE VARIOUS RESTRS. IN PARTICULAR I MONITORED THE 30 MILE SEPARATION FROM WASHINGTON NATIONAL CLOSELY -- THE DME DOES NOT REGISTER AT LOW ALTS IN THAT SECTOR SO I USED GPS AND HAD GREATER THAN 30 MILES SEPARATION WHEN IT WAS ABEAM. KNOWING THAT OTHER PLTS HAD TROUBLE WITH THE ADIZ OVER THE WATER NEAR QUANTICO; I CONTINUED W AND S OF BRV VOR AND APCHED EZF FROM THE S OVER THE RAPAHANNOCK RIVER. UPON LNDG I WAS TOLD TO CALL CUSTOMS AND THEN THE PCT FAA WHO SAID I HAD BEEN FOUR OR FIVE MILES INSIDE THE ADIZ TO WHICH I POLITELY BUT FIRMLY EXPRESSED SHOCK AND DISBELIEF AND EXPLAINED THE ABOVE. I HAVE BEEN FLYING IFR TO THE MAXIMUM EXTENT FEASIBLE IN THE DC AREA INCLUDING FLTS INTO FME AND W29 (AND INCIDENTALLY THE 05/SUN/03 MORNING FLT FROM EZF TO MIV). I DID NOT DO SO THIS TIME AS THERE WERE SOME 20 PLUS DEPARTING AT MIV AND FELT COMFORTABLE WITH THE RTE. I WILL DO SO IN THE FUTURE.