CLOSE PROX 2 COMMUTER LTT ACFT. 1 ON APCH TO RWY 18 THE OTHER ON CLB OUT FROM RWY 36.

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AUG; 1991; DEPARTING FROM THE GOLDEN TRIANGLE ARPT IN COLUMBUS; MS; 2 COMMUTER ACFT CAME WITHIN LESS THAN A MI OF ONE ANOTHER. FLT XXX REQUESTED CLRNC FROM GTR ON THE GND AS WE HELD SHORT OF RWY 36 AT GTR. WE WERE ASKED IF WE COULD ACCEPT AN IMMEDIATE RELEASE WITH A 2 MIN VOID TIME; 'TURN NOW 36; VOID IF NOT OFF BY 38'. WE ACCEPTED THE RELEASE; COMPLETED A BRIEF BEFORE TKOF CHKLIST AND TOOK OFF WELL INSIDE THE CLRNC WINDOW. IN FACT; ONLY 1 MIN ELAPSED BEFORE WE WERE DEPARTING RWY 36 (WE DEPARTED 36 AS THE WINDS WERE CALM AND OUR FLT PATH ON COURSE WOULD HAVE BEEN 030). AFTER AIRBORNE; DEP CTL ANSWERED US ON OUR THIRD CALL OUT OF GTR WITH A 'FLT XXX MAINTAIN VFR'. I LOOKED OUT THE WINDOW TO OUR R; AND SAW ANOTHER COMMUTER ACFT DEVIATING L OF THE APCH COURSE (FOR RWY 18) UPON DIRECTION TO DO SO IMMEDIATELY BY THE DEP CTLR. FLT VISIBILITY WAS ABOUT A MI AND I TOLD THE CTLR WE WERE UNABLE TO MAINTAIN VFR AND THAT I SAW THE OTHER ACFT VERY CLOSE TO US. THERE WAS NO RESPONSE FROM THE CTLING FACILITY ABOUT MY SEEING THE OTHER ACFT. THE CAPT ASKED 'WHAT HAPPENED BACK THERE; WE ARE ON AN INST FLT PLAN?' THE CTLING FACILITY TOLD US WE HAD MISSED OUR VOID TIME. WHAT I BELIEVE HAPPENED WAS THE CTLR CLRED THE OTHER COMMUTER ACFT FOR THE 18 APCH INTO GTR IMMEDIATELY UPON EXPIRATION OF OUR VOID TIME ASSUMING WE WERE NOT AIRBORNE; EVEN THOUGH WE ACCEPTED THE VOID TIME AND HAD NOT SUBSEQUENTLY INFORMED THEM OTHERWISE. WE MAY NOT HAVE HAD CONTACT WITH THE CTLR BY XA38 BUT WE CERTAINLY WERE AIRBORNE PRIOR TO THAT TIME. THE WX AT THE TIME WAS SKY OBSCURED AND 1 MI VISIBILITY ON THE SURFACE. THE CTLR NEVER ASKED US WHICH RWY WE WOULD BE DEPARTING; NOR DID CTLR INFORM US CTLR HAD AN INBOUND FOR THE INST APCH TO RWY 18. THERE WAS AT LEAST 1 OTHER ACFT THAT IDENTED THEMSELVES AS A WITNESS TO OUR TRYING TO CONTACT DEP CTL WITHIN THE CLRNC WINDOW.