PLT OF SMA CONCERNED OVER PROC USED IN PROX OF 2 ARPTS AND TFC ARSA SEPARATION PROC USED.

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TWIN LAUNCHED FROM GMU FROM RWY 18 (RWY 27 WAS IN USE). WE WERE IN CONTACT WITH GMU TWR; ASKED FOR NDG 36 TRACK TO L DOWNWIND FOR 27. TWR GAVE US L BASE TO 27 OR WAIT AT JUDKE FOR TWIN TFC TO PASS. ELECTED TO HOLD AT JUDKE. TFC PASSED AT OUR ALT AS WE COMPLETED HOLDING OUTBOUND TURN (X MARK). WE HAD VISUAL CONTACT WITH HIM BUT HE WAS TALKING TO GREER APCH BY THAT TIME. SINCE WE WERE STILL ON TWR; A POSSIBLE CONFLICT COULD HAVE OCCURRED. WE SHOULD HAVE BEEN ON GREER APCH ALSO; SO BOTH CTLRS WOULD HAVE KNOWN ABOUT US; AND WE WOULD HAVE BEEN TAGGED. I THINK WE ALSO CLIPPED THE EDGE OF THE E HALF OF THE 5000/2100 ARSA SECTOR WHILE HOLDING. PREVENTION: WHEN COMING IN FROM THE S; SEQUENCE WITH GREER ARSA PRIOR TO CONTACTING GMU TWR; EVEN WHEN COMING IN UNDER THE ARSA. THE GMU HOLDING PATTERN IS TOO CLOSE TO THE E SECTOR OF ARSA TO GUARANTEE STAYING OUT OF ARSA SECTOR. (I CALLED GREER APCH SUPVR ON DUTY AND HE SUGGESTED THE ABOVE. NEXT TIME WE'LL CALL APCH CTL AND LET HIM SEQUENCE US TO TWR.)