A PA28 CFI DID NOT CANCEL IFR FLT PLAN IN A TIMELY FASHION WHEN OPERATING WITHIN THE DC ADIZ; AND IN A NON TWRED ARPT.

Narrative

IFR FILED PLAN FROM ESN TO GAI (EASTERN; MD TO GAITHERSBURG; MD) WHICH HAS GAI IN WASHINGTON ADIZ. CTLR WAS BUSY. I HAD VFR PLT CHKING OUT IN HIGH PERFORMANCE ACFT. CTLR ASKED IF I WAS 'FAMILIAR.' I ASKED; 'WITH WHAT?' CTLR SAID 'CANCELLATION PROC.' I SAID; 'YES.' WHEN GAI WAS IN SIGHT; WE REQUESTED LOWER ALT. ATC GRANTED AND GAVE US VISUAL AND I SAID WE WOULD MAINTAIN 'SQUAWK TO GND.' I GOT BUSY WITH THE 'SLAM DUNK' APCH (VISUAL) BY TRAINEE. LANDED WITHOUT EVENT BUT DIDN'T CANCEL IFR UNTIL WE HAD PUSHED ACFT BACK INTO ITS TIE-DOWN (LESS THAN 10 MINS). I CANCELED WITH POTOMAC CLRNC ON GND REMOTE WHICH IS STANDARD AND THEY ACKNOWLEDGED. WE USUALLY CANCEL ON THE TXWY. I DROPPED THE BALL; PROBABLY; BECAUSE I HAD FLOWN INTO THIS ARPT ABOUT 4 TIMES IN THE PAST WEEK VFR WITH AN ADIZ XPONDER CODE WHICH IS MAINTAINED TO THE GND. BUT; VFR; THERE IS NOTHING TO CANCEL. I BELIEVE IT IS WORTH ATC COM TIME TO REITERATE 'CANCEL IN THE AIR OR ON THE GND' ON PARTING COM TO ACFT. NO DAMAGE OR DELAYS DONE HERE; BUT THE AREA IS BUSY AND 10 MIN CANCELING DELAYS WOULD BE A PROB.