FLC OF BAE800A EXTENDS DOWNWIND AFTER CANCELING IFR FLT PLAN TO ASSURE SEPARATION FROM ACFT THEY ARE FOLLOWING ON APCH. THEY PROBABLY ENTERED CLASS B AIRSPACE WITHOUT CLRNC.

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WE WERE ON AN IFR FLT INTO THE ROCK HILL ARPT; APCHING FROM THE E; AND CLRED FOR THE VISUAL APCH BY CHARLOTTE ATC. ACTIVE RWY AT ROCK HILL WAS RWY 20 WITH L TFC. AS ATC SWITCHED US OVER TO ADVISORY FREQ; WE CANCELED OUR IFR FLT PLAN. THIS IS OUR USUAL PROC IN GOOD VMC; DEVELOPED FROM OPERATING OUT OF A BUSY UNCTLED HOME ARPT TO ACCOMMODATE OTHER IFR TFC WAITING ON THE GND OR FOR THE APCH BEHIND US. UPON ENTERING THE DOWNWIND AT 1500 FT AGL TO MAINTAIN SEPARATION FROM SLOW TFC IN THE PATTERN AND ANNOUNCING OUR POS; WE HEARD BUT DID NOT SEE A LIGHT ACFT CALL 'DOWNWIND ABOUT TO TURN BASE LEG.' WHILE ATTEMPTING TO VISUALLY LOCATE THIS ACFT IN FRONT OF US; TO MAINTAIN PROPER SEPARATION; WE EXTENDED OUR DOWNWIND LEG AND DELAYED OUR DSCNT OUT OF PATTERN ALT. UPON HEARING THE OTHER ACFT RPT SHORT FINAL; WE TURNED BASE AND COMPLETED OUR APCH AND LNDG. AFTER LNDG AND SEEING A LARGE SCALE VFR CHART ON THE WALL IN THE FBO FLT PLANNING ROOM; WE DISCOVERED THAT BY EXTENDING OUR DOWNWIND AND DELAYING OUR DSCNT; WE MAY HAVE INADVERTENTLY PENETRATED THE EDGE OF THE CHARLOTTE CLASS B AIRSPACE. WHILE IT IS TRUE THAT IF WE HAD WAITED TO CANCEL OUR IFR FLT PLAN ON THE GND; WE WOULD NOT BE CONCERNED WITH THIS ISSUE; I BELIEVE HAVING 'B' CLASS AIRSPACE SO CLOSE TO A SECONDARY ARPT TFC PATTERN IS A SET-UP FOR HIGH PERFORMANCE ACFT. THERE SHOULD BE A 4-5 MI RING AROUND SUCH ARPTS CLRING THE TFC PATTERN AREA FOR ALL LEVELS OF PERFORMANCE ACFT AND ALLOWING THE NECESSARY MANEUVERING ROOM FOR VARIOUS SITS.