AFTER LEAVING THE DC ADIZ A PA28 PLT DEVIATES SLIGHTLY FROM HIS COURSE AND DRIFTS BACK INTO THE ADIZ WITHOUT CLRNC.

Narrative

DEPARTING HEF ON A VFR/ADIZ FLT PLAN; I CONTACTED PCT APCH WHEN INSTRUCTED BY HEF TWR. I WAS RADAR IDENTIFIED AND PROCEEDED ON-COURSE; BEING REMINDED TO NOT ENTER THE CLASS B AIRSPACE. MY COURSE WAS FILED WITH ELKINS FSS AS CSN VOR; MRB VOR; AND THENCE TO MRB ARPT. I HAD FILED THE ENTIRE RTE AS THE PATH FROM CSN TO MRB IN RIGHT ON THE EDGE OF THE DC ADIZ. AS I APCHED CSN; PCT INFORMED ME THAT I WAS EXITING THE ADIZ; AND TO SQUAWK 1200 (WITH) FREQUENCY CHANGE APPROVED. THE PCT CTLR SEEMED VERY BUSY; I DIDN'T COMPLAIN AND WENT ON MY WAY. WINDS WERE LIGHT; BUT I WAS APPROX 1 NM E OF MY COURSE; AS I CROSSED UPPERVILLE ARPT ON ITS EASTERN EDGE AS OPPOSED TO ITS WESTERN. MY MISTAKE WAS TO ASSUME THAT MY PLAN WAS STILL ACTIVE AT THIS POINT. MY ASSUMPTION WAS THAT; AKIN TO AN IFR FLT; ONLY RADAR SERVICES WERE TERMINATED; BUT MY PLAN WAS STILL ACTIVE. APCHING UPPERVILLE; I HEARD A CALL TO 'ACFT S OF UPPERVILLE' NOTIFYING ME (THERE WERE NO OTHER ACFT NEAR) THAT I WAS IN THE DC ADIZ AND SUGGESTING THAT I EXIT THE AREA IMMEDIATELY. I TUNED DIRECTLY W AND MAINTAINED MY ALT; THEN RESPONDED ON 121.5 THAT 'CHEROKEE WAS ON A FLT PLAN AND WOULD CONTACT PCT APCH.' CONTACTING PCT APCH; THEY RECOGNIZED THE SIT AND ASKED FOR MY REQUEST. I REQUESTED MY SQUAWK; BUT THEY INDICATED THAT FROM MY (THEN) PRESENT POS TO MRB WAS OUTSIDE THE ADIZ. THE CTLR THEN SUGGESTED A NEW FREQ OF PCT IN THAT AREA FOR FURTHER ASSISTANCE. BY THE TIME I HAD TURNED THAT FREQUENCY AND WAITED FOR CLR FREQUENCY; PCT WAS CALLING ME UP WITH A NOTIFICATION OF A POSSIBLE 'PLT DEVIATION' AND GIVING ME A NUMBER (PCT APCH) TO CALL UPON LNDG. I CONTINUED TO MRB ARPT AND LANDED WITHOUT INCIDENT. THE EVENT COULD HAVE BEEN AVOIDED HAD I INSISTED UPON KEEPING A SQUAWK CODE; OR FAILING THAT VERIFYING WITH APCH THAT MY RTE OF FLT WOULD MISS THE ADIZ AS I PROCEEDED N. AS WELL; THOUGH ATC IS OVERLOADED WITH VFR FLTS DUE TO THE ADIZ; ATC NEEDS TO PAY MORE ATTENTION TO THE FLT PLANS; NOT ASSUMING THAT ALL VFR FLTS ARE ACHING TO EXIT THE ADIZ.