ACR-LGT VECOTRED AND CLIMBED INTO CONFLICT WITH ACR-LGT ARR RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative

WE WERE ON A RIGHT DOWNWIND FOR RWY 27; IAH; LEVEL AT AN ASSIGNED ALT OF 6000' AND ON AN ASSIGNED HDG OF 080 DEGS. THE APCH CTLR CALLED OUT TFC AT 2 O'CLOCK; CLBING FROM 4000 TO 5000'. WE CALLED HIM IN SIGHT. HE APPEARED TO BE ON A ROUGHLY PARALLEL COURSE WELL BELOW US. APPROX 1 MIN LATER WE LOOKED OUT THE RIGHT SIDE AND SAW LGT Y COMING DIRECTLY AT US; CLBING THROUGH OUR ALT. ANY MANEUVER ON MY PART OTHER THAN A DSCNT WOULD HAVE AGGRAVATED THE SITUATION. PRIOR TO COMMENCING A DSCNT TO AVOID THE OTHER ACFT; WE OBSERVED HIM COMMENCE A HARD LEFT TURN AND REALIZED HE WOULD PASS BEHIND US. I ESTIMATE THAT HE CAME WITHIN 1/2 MI AT THE CLOSEST POINT. I RPTED THE INCIDENT IMMEDIATELY TO THE APCH CTLR AND; WHEN ON THE GND; I CALLED THE AREA MGR; AND DISCUSSED THE INCIDENT. HE TOLD ME THAT THEY (DEP CTL) HAD CLBED HIM THROUGH MY ALT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: AS STATED IN NARRATIVE; RPTR CALLED THE TRACON BY TELEPHONE AND LEARNED THAT THE DEP CTLR HAD MISTAKENLY CLBED A DEP THROUGH THE ARR CORRIDOR. THE CLBING DEP PASSED APPROX 1/2 MI BEHIND RPTR'S ACFT AT THE SAME ALT.