CPR ACFT TAKES EVASIVE ACTION DURING INITIAL CLB AS SMT CLOSES INTO FLT PATH.

Narrative

FLYING AN SMT TWIN FROM CGX TO SPI WE COULD HAVE HAD A TFC CONFLICT WHILE DEPARTING CGX ON AN IFR FLT PLAN. THE WX WAS NOT A PROB. I REMEMBER FAIRLY HIGH CLOUD LAYERS OF AT LEAST 5000 TO 6000 FT; BROKEN WITH UNLIMITED VISIBILITY. WE CALLED FOR OUR CLRNC AND RECEIVED OUR IFR CLRNC ROUTING TO SPI. WE WERE CLRED TO TAXI TO RWY 36 FOR DEP. THERE WERE SEVERAL ACFT WAITING FOR DEP WHICH PUT US IN LINE FOR 5 TO 6 MINS BEFORE DEP. WE WERE LISTENING TO TWR FREQ THIS ENTIRE TIME. WE WERE RELEASED AND CLRED FOR DEP WITH A HDG OF 140 DEGS AND INITIAL ALT OF 2000 FT. WE TOOK OFF AND PASSING 1000 FT STARTED A TURN TO 140 (R TURN). TWR SWITCHED US TO DEP FREQ OF 118.4. CHKED IN WITH DEP AND THEY IMMEDIATELY GAVE US A CLRNC TO 6000 FT. I WAS SITTING IN THE R SEAT AND WAS LOOKING OUT THE WINDOW AND OBSERVED A TWIN ENG ACFT RAPIDLY FILLING THE WINDOW. I GRABBED THE CTLS AND INITIATED A DSCNT. WE HAD APEXED AT ABOUT 2200 FT. AFTER WE BOTH VISUALLY CLRED OURSELVES WE RESUMED A NORMAL CLB TO 6000 FT. ONCE WE WERE STABLE AND LEVEL AT 6000 FT I CALLED CGX TWR TO ASK IF THEY KNEW ABOUT THE OTHER ACFT. THEY REPLIED THAT THEY DID AND THAT HE WAS 500 FT HIGHER THAN US. I INFORMED THEM THAT WE HAD BEEN IMMEDIATELY CLRED TO 6000 FT BY DEP AND WERE SURPRISED TO SEE TFC SO CLOSE TO US. WE BOTH TALKED THIS OVER AND NEITHER ONE OF US CAN REMEMBER HEARING TWR TALK TO A NBOUND TWIN ENG ACFT WHILE WE WERE TAXIING OUT OR SITTING IN LINE. TWR GAVE US CLRNC FOR TKOF BUT DID NOT INFORM US OF THE OTHER TFC. IMMEDIATELY AFTER TKOF AND WHILE WE WERE WITHIN THE CGX ATA; THEY SWITCHED US OVER TO DEP. (THIS IS SOP FOR CGX.) ONLY DILIGENCE IN LOOKING OUTSIDE PREVENTED US FROM HAVING A REAL CLOSE ENCOUNTER. I WOULD ESTIMATE THAT WE WERE WITHIN 300 FT VERTICALLY AND ABOUT 1500 FT HORIZ WHEN I OBSERVED THE OTHER ACFT. TOO CLOSE. TWR SHOULD UNDERSTAND THAT WHEN THEY HAND ACFT OFF TO DEP THEY HAVE FORFEITED CTL AND ANY PREVIOUS ALT SEPARATION CAN BE NULLIFIED BY ADDITIONAL ALT CLRNC GIVEN BY DEP.