SUBSEQUENT TO FAILURE OF HIS GPS; SINGLE PLT OF SMA ENTERED DC ADIZ.

Narrative

ON A SHORT RETURN FLT TO HOME BASE AT WARRENTON; VA; ARPT (MIDLAND; VA) W66 FROM CULPEPPER; VA; ARPT; MY GPS FAILED. FROM THE TIME OF DEP AT CULPEPPER ARPT MY XPONDER WAS ON AND RPTING THE VFR 1200 CODE. THE GPS HAVING FAILED; I REVERTED TO VOR AND DME. DECIDING TO INTERCEPT THE 115 DEG RADIAL OF CAS VOR 116.3 AT ABOUT 7-10 MI I SET THE OBS FOR 115 DEGS AND WATCHED NEEDLE INDICATIONS FOR A RADIAL XING. NOT SEEING WHAT I EXPECTED; WHEN I THOUGHT I SHOULD; I SET THE DME TO 116.3 AND NOTICED A DISTANCE OF 11+ MI. REALIZING THAT I WAS PAST THE ARPT AND APCHING THE QUANTICO RESTR AREA; I TURNED RIGHT TOWARD THE ARPT AND SAW THE WARRENTON RWY. I LANDED ON RWY 32 AS PLANNED. UPON LNDG AND TAXIING TO MY HANGAR; THE LINE PERSON MET ME AND SAID THAT POTOMAC TRACON WOULD LIKE ME TO CALL THEM. AFTER PROVIDING MY PLT CERTIFICATE AND PHONE NUMBER; TRACON STATED THAT I HAD ENTERED THE 30 MI ADIZ RING FROM DCA WITHOUT PERMISSION AND WOULD BE CITED FOR AN INCURSION. THEY ALSO SAID THAT THEY LOST TRACK ON ME (PERHAPS REFERRING TO SKIN PAINTING) BUT THAT THEY (OR SOMEONE ELSE) SAW MY XPONDER SQUAWKING 1200 ALL THE WAY TO THE ARPT. THEY ALSO SAID THAT THEY HAD TO SUBMIT A PRELIMINARY RPT AND THAT I WOULD BE CONTACTED BY THE FSDO IN 3-5 DAYS FOR FURTHER ACTION. DURING THE FLT WHEN I NOTICED THAT I WAS SOMEWHAT OFF MY EXPECTED TRACK; I CORRECTED THE SIT AND HEADED DIRECTLY FOR THE WARRENTON ARPT AND AT NO TIME TOOK ANY EVASIVE ACTION. I DIDN'T THINK I HAD DONE ANYTHING WRONG; AND I'M NOT SURE I DID NOW. IT IS INTERESTING TO NOTE THAT TRACON ASKED ME SEVERAL TIMES IF I WAS SQUAWKING 1200 AND I SAID THAT I WAS. I ENCOUNTERED ANOTHER SMALL GA ACFT AT JUST ABOUT THE SAME TIME THAT I MADE A R TURN TO THE WARRENTON ARPT WHEN I WAS ABOUT ON THE 110 DEG CAS RADIAL. THE OTHER ACFT WAS ABOVE ME ABOUT 500-800 FT. TRACON SAID THAT ANOTHER ACFT HAD BEEN CONTACTED BY MANASSAS TWR AND THAT THEY HAD SEEN ANOTHER ACFT IN THIS GENERAL AREA BUT DID NOT IDENT IT; AS THERE WERE NUMEROUS ACFT IN THE VICINITY OF THE WARRENTON ARPT AT THE TIME. I'M STILL NOT SURE TRACON CORRECTLY IDENTED MY ACFT OR WHICH 1200 ACFT THEY WERE TRACKING.