GA ACFT LNDG IN THE WASHINGTON ADIZ AREA; CANCELS IFR; CHANGES XPONDER TO 1200; THEN CONDUCTS 2 GAR'S BEFORE LNDG.

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PRIOR TO DEP FROM ST LOUIS FOR CARROLL COUNTY ARPT; I PURCHASED APCH PLATES FOR ARPTS IN MARYLAND AND SECTIONAL CHARTS FOR THE RTE AS WELL. THE SECTIONALS INCLUDED THE VFR TERMINAL AREA CHART BALTIMORE-WASHINGTON. IN ADDITION; I VISITED THE FAA WEB SITE FOR THE WASHINGTON TRI-AREA CLASS B AIRSPACE. I PRINTED A DRAWING OF THE WASHINGTON; DC; ADIZ AVAILABLE FROM THE WEB SITE AS WELL AS THE LIST OF PHONE NUMBERS AND FREQS FOR POTOMAC APCH/DEP CTL. I ALSO PRINTED THE PROCS FOR PATTERN AND DEP OPS FOR ARPTS IN THE ADIZ. THESE INCLUDED MARYLAND ARPT; MY DEST AFTER DEP FROM CARROLL COUNTY REGIONAL. AFTER COMPLETING OUR FLT TO CARROLL COUNTY REGIONAL; I PLANNED A FLT TO MARYLAND ARPT. MY CONCERN ABOUT FLYING IN THE ADIZ; AND THE POSSIBILITY OF MAKING AN ERROR; PROMPTED ME TO FILE A FLT PLAN THAT AVOIDED FLYING IN MUCH OF THE ADIZ. THUS; I FILED AN IFR FLT PLAN FOR A RTE FROM CARROLL COUNTY REGIONAL VIA WESTMINSTER (EMI); MARTINSBURG (MRG); LINDEN (LDN) AND CASANOVA (CSN); ALL OF WHICH ARE OUTSIDE THE ADIZ. FROM CASANOVA; I PLANNED TO ENTER THE ADIZ AND FLY DIRECT TO THE DEST (MARYLAND ARPT). THE LEG FROM CASANOVA TO MARYLAND ARPT INCLUDED A SMALL BEND IN THE COURSE TO AVOID RESTR AREA R6608A. WHEN I RECEIVED THE CLRNC AT CARROLL COUNTY REGIONAL; IT WAS TOTALLY DIFFERENT FROM THE FLT PLAN I FILED. IT WAS MUCH SHORTER; ONLY 76 NM; WHICH I APPRECIATED; BUT ABOUT 90% OF THE NEW RTE ASSIGNED TO ME WAS INSIDE THE ADIZ; AN OPPORTUNITY FOR A PROB IN MY VIEW. THIS NEW FLT PLAN SPECIFIED THAT I 'ENTER CTLED AIRSPACE AT WESTMINSTER VOR; FLY DIRECT BAL; DIRECT OTT; DIRECT 2W5. MAINTAIN 3000 FT; EXPECT 5000 FT AFTER 10 MINS. CONTACT POTOMAC APCH ON 125.2; SQUAWK XXXX.' SHORTLY AFTER PASSING EMI; I WAS CLRED TO 6000 FT. WE CONTINUED TO BALTIMORE. AFTER PASSING NOTTINGHAM; WE WERE CLRED TO 4000 FT; THEN 3000 FT; THEN 2000 FT; THEN 1500 FT. FINALLY; I WAS CLRED TO 1200 FT. WHEN I RPTED MARYLAND ARPT IN SIGHT; I WAS TOLD TO CONTACT THE ARPT FOR LNDG INFO AND TO CANCEL THE FLT PLAN EITHER IN THE AIR OR ON THE GND AT A SPECIFIC TELEPHONE NUMBER. WITH THE ARPT IN SIGHT; I CANCELED IMMEDIATELY. NEXT; I DID WHAT I WAS ALWAYS TOLD TO DO; 'SQUAWK 1200' (VFR). UNFORTUNATELY; TFC CONGESTION AT MARYLAND ARPT CAUSED ME TO ABORT 2 ATTEMPTS TO LAND. CONSEQUENTLY; AFTER ABORTING; I FLEW CIRCULARLY TWICE TO RE-ENTER FINAL. THIS RESULTED IN FLYING IN THE AREA LONGER THAN ORDINARILY WOULD BE NECESSARY TO LAND AFTER I CANCELED THE FLT PLAN. IT OCCURS TO ME THAT A SLIGHT CHANGE IN THE CTLRS' PROC MIGHT BE A WELCOME BENEFICIAL ADJUSTMENT. THIS IS IN CONSIDERATION OF THE FACT THAT CTLRS THROUGHOUT THE US; ON RECEIVING A FLT PLAN CANCELLATION; ADVISE THE PLT; 'CANCELLATION RECEIVED; SQUAWK 1200.