A BE58'S XPONDER FAILED IN DCA ADIZ PRIOR TO LNDG.

Narrative

I WAS OPERATING ON AN IFR FLT PLAN UNDER FAR PART 135. IT WAS A NORMAL FLT AND ARR INTO THE MANASSAS AREA WITH AN IFR HDOF TO THE CTL TWR FOR A VISUAL APCH. AFTER ARRIVING AT THE LCL FBO; I HAD A CALL FROM GND CTL ABOUT A RPT FROM APCH THAT MY XPONDER DROPPED OFF THEIR SCOPE. I WAS INSTRUCTED TO CALL THE UNITED STATES DEPT OF HOMELAND SECURITY; AND I DID. I WAS INFORMED AT THAT TIME THAT MY XPONDER HAD DROPPED OFF RADAR DURING THE APCH AND THEY WERE CONDUCTING A ROUTINE INVESTIGATION. THE MOOD WAS ONE OF FORMALITY; AND THERE DID NOT SEEM TO BE ANY GREAT CONCERN AS NO ONE CAME TO THE ARPT TO PERSONALLY INTERVIEW ME. AT NO TIME INFLT DID APCH OR TWR INFORM ME OF ANY PROB WITH MY XPONDER. THUS; I NEVER HAD ANY KNOWLEDGE OF; OR OPPORTUNITY TO RECTIFY THE MALFUNCTION. AFTER SPEAKING WITH HOMELAND SECURITY; I IMMEDIATELY WROTE UP THE XPONDER ON THIS ACFT FOR MAINT. I AM THOROUGHLY KNOWLEDGEABLE IN THE PROCS FOR FLYING THE ADIZ; AS I DO SO EVERY WKDAY ON A STRICT SCHEDULE. I STARTED FLYING INTO THE ADIZ IN MID JUL/04 AND DID NOT HAVE ANY RPTED PROBS UNTIL AUG/MON/04 AND HAVE NOT HAD ANY SINCE. I MAINTAIN THE HIGHEST OF PROFESSIONALISM IN ALL OPS. AT NO TIME DID I TOUCH THE XPONDER DURING FLT; THEREFORE; THE ONLY POSSIBLE EXPLANATION IS A XPONDER FAILURE; EITHER TOTAL OR INTERMITTENT; OR A FAILURE IN ATC RADAR PERFORMANCE.