UNAUTH PENETRATION OF AIRSPACE WHEN THE PVT PLT OF BE24 IS DISTR WITH A WX ENCOUNTER AND INADVERTENTLY AND PREMATURELY ENTERS THE SPECIAL USE AIRSPACE OF DC ADIZ.

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I DEPARTED FROM HEF; WHICH IS WITHIN THE WASHINGTON DC ADIZ; AT XA30 UNDER A VFR ADIZ FLT PLAN FILED WITH FSS LEESBURG. THE FLT PLAN WAS DIRECT TO THE CASANOVA VOR (CSN); WHICH LIES OUTSIDE OF THE WASHINGTON DC ADIZ. A RETURN FLT PLAN WAS FILED AT THE SAME TIME FOR REENTRY INTO THE ADIZ APPROX 1 1/2 HRS LATER FROM THE VICINITY OF THE CASANOVA VOR. THIS PROC IS ADVOCATED BY FAA PERSONNEL AT FAA SAFETY SEMINARS AND USED BY ME ON DOZENS OF OCCASIONS IN THE PAST; ALL WITHOUT INCIDENT. THE PURPOSE OF THIS FLT WAS TO PRACTICE ILS APCHS (STRICTLY VFR WITHOUT VISION LIMITING DEVICES) INTO WINCHESTER REGIONAL ARPT (OKV). THE CASANOVA VOR IS AN IAF FOR THIS PROC; THENCE ALONG THE 355 DEG RADIAL INTERCEPTING THE WINCHESTER LOC (I-TZX) AT THE CLADD INTXN. I MADE 2 APCHS; ENDING EACH WITH A MISSED APCH AS PUBLISHED. IT WAS MY INTENT; UPON REACHING THE CLADD INTXN ON THE COMPLETION OF THE SECOND MISSED APCH; TO INTERCEPT THE CASANOVA 355 DEG RADIAL FOR A RETURN TO CASANOVA. AT CASANOVA I WOULD REQUEST REENTRY INTO THE WASHINGTON ADIZ FROM ATC AS PER FILED FLT PLAN. AT 1-2 MI FROM THE CLADD INTXN AS PER DME; I WAS CONFRONTED WITH APCHING DARK CLOUDS CONSIDERABLY BELOW MY ALT OF ABOUT 3500 FT MSL; APPROX 2 MI DISTANT. I IMMEDIATELY REDUCED PWR AND COMMENCED A DSCNT TO REMAIN CLR OF CLOUDS. UPON ATTAINING A SAFE ALT BENEATH THE CLOUDS I NOTICED THAT I HAD GONE PAST THE CLADD INTXN; WHICH IS 2-3 MI OUTSIDE THE ADIZ AND I IMMEDIATELY TURNED S TO INTERCEPT THE CASANOVA 355 DEG RADIAL INBOUND TO CASANOVA. I CONTACTED ATC NEAR CASANOVA AND REQUESTED REENTRY INTO THE ADIZ; WHICH WAS GRANTED; AND PARENTHETICALLY; TOLD TO CONTACT POTOMAC APCH AFTER LNDG. POTOMAC APCH ALLEGED THAT I HAD PENETRATED THE ADIZ IN THE VICINITY OF UPPERVILLE; A PVT AIRSTRIP LOCATED JUST INSIDE THE ADIZ.