FLC OF A BRITISH BA3200 DID NOT RESPOND TO THE TWR CTLR'S REQUEST TO TURN R DURING INITIAL IFR CLB DUE TO DEP PROC INSTRUCTING TO MAINTAIN RWY HDG TO ASSURE OBSTRUCTION CLRNC UNTIL REACHING A SPECIFIED ALT OF WHICH THEY HAD NOT YET REACHED.

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DEPARTED RWY 21. WE WERE ADVISED TO EXPEDITE DEP DUE TO INBOUND ACFT 16 MI OUT. TKOF CLRNC WAS 'CLRED FOR TKOF; TURN R ON COURSE.' THE OBSTACLE CLRNC DEP PROC SPECIFIES: CLB ON RWY HDG TO 4000 FT BEFORE PROCEEDING ON COURSE. WE FOLLOWED THE PROC AND PLANNED TO TURN ON COURSE AFTER PASSING 4000 FT. HOWEVER; THE ARR ACFT WAS INBOUND ON THE ILS RWY 3 APCH INTENDING TO CIRCLE TO LAND ON RWY 21. AFTER TKOF; THE TWR TOLD US TO TURN R ON COURSE. WE ADVISED HIM THAT WE WERE UNABLE TO MAKE AN IMMEDIATE TURN DUE TO THE DEP PROC. HE THEN TOLD US TO TURN R; ENTER A R DOWNWIND AND LAND. WE TOLD HIM WE WERE UNABLE. HE THEN TURNED THE ARR ACFT OFF THE APCH. WE RECEIVED A TFC ALERT DURING THE DEP. WE ESTIMATE THAT THE CLOSEST THE 2 ACFT CAME HORIZLY WAS 3 NM; AND THE CLOSEST VERTLY WAS 300 FT. WE MOMENTARILY STOPPED OUR CLB AND TURNED SLIGHTLY R TO AVOID THE TFC. PASSING 4000 FT WE TURNED ON COURSE. CONTRIBUTING FACTORS TO THIS CONFLICT WERE THE FACT THAT WE DIDN'T KNOW WHAT APCH THE INBOUND ACFT WAS ON. ALSO; THERE IS A COMMUTER AIRLINE BASED AT CHO WHICH ROUTINELY DISREGARDS THIS DEP PROC AND THE TWR HAS THEREFORE BECOME ACCUSTOMED TO THIS AND HAS AN EXPECTATION THAT OTHER ACFT WILL MAKE AN IMMEDIATE TURN AFTER TKOF. FURTHERMORE; THE CHO CTL TWR HAS AN LOA ON FILE WITH THE CHIEF PLT OF MY COMPANY WHICH SPECIFIES THAT 'IF YOUR TKOF CLRNC IN VISUAL CONDITIONS INCLUDES THE PHRASE 'CLRED ON COURSE;' YOU ARE NOT REQUIRED NOR EXPECTED TO FOLLOW THE PUBLISHED IFR DEP PROC. YOU MAY TURN ON COURSE WHEN ALT AND OBSTRUCTION CLRNC PERMIT.' THIS INSTRUCTION APPEARS IN MY AIRLINE'S FOM; HOWEVER; IT APPEARS A LITTLE VAGUE WHAT EXACTLY IS MEANT BY 'VISUAL CONDITIONS.' THIS MAY HAVE CAUSED THE CONFUSION BTWN THE CTLR'S AND MY EXPECTATION OF OUR FLT PATH AFTER DEP.