NMAC BTWN A C172 TURNING XWIND AFTER TKOF AND A C150 THAT HAD JUST TURNED DOWNWIND WHICH TOOK OFF AHEAD OF THE RPTR'S C172. THE C150 WAS OBSERVED IN A DIVING TURN TO AVOID A COLLISION WITH THE RPTR.

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WHEN I CALLED FOR TKOF CLRNC; I ADVISED TWR THAT I WAS EBOUND. I WAS CLRED FOR TKOF BEHIND A DEPARTING C150. ON TKOF; THE CTLR ASKED FOR MY DEP DIRECTION. I AGAIN TOLD HER 'EBOUND.' SHE REPLIED EITHER 'CLRED ON COURSE AT DEP END' OR 'TURN ON COURSE AT DEP END.' SHE DID NOT GIVE ANY TA'S. OVER THE DEP END OF THE RWY; I CHKED FOR AN AIRPLANE I KNEW TO BE DOWNWIND ON THE PARALLEL RWY; THEN TURNED R ON COURSE. ABOUT 30 SECONDS LATER; I SAW THE C150 TO MY L; DIVING AND TURNING BEHIND ME. I HAD NOT GOTTEN HIS DEP DIRECTION; BUT IT WAS APPARENTLY SOUTHERLY. HIS CLBOUT; XWIND; DOWNWIND COURSE PUT HIM ON A COLLISION COURSE WITH MY XWIND. PREOCCUPIED WITH THE KNOWN DOWNWIND TFC AND ASSUMING THAT THE TWR'S 'DEP END' CLRNC HAD TAKEN OTHER TFC INTO ACCOUNT; I HADN'T SCANNED EFFECTIVELY AND MISSED THE PLANE THAT HAD DEPARTED BEFORE ME. LESSONS LEARNED: 1) THIS CONFLICT WOULD NOT HAVE OCCURRED AT AN UNCTLED FIELD -- I WOULD NEVER HAVE TURNED WITHOUT KNOWING EXACTLY THE LOCATION OF THE PREVIOUS DEP. I WAS LULLED BY THE CTLR'S CLRNC TO TURN AT THE DEP END OF THE RWY. 2) A CTLR'S CLRNC TO TURN DOES NOT MEAN IT'S SAFE TO DO SO. CHK WITH YOUR OWN EYES! 3) A CTLR THAT MISSES SOMETHING (MY DEP DIRECTION) MAY BE OVERLOADED OR DISTR AND IS LIKELY TO MISS OTHER ACFT ON COLLISION COURSES.