RPTR'S ACFT X WAS RETURNING TO ATL BECAUSE OF A GEAR PROB. WHILE BEING VECTORED TO THE RWY; ACFT X CAME WITHIN CLOSE PROX OF ACFT Y ON APCH TO THE ADJACENT RWY. STANDARD SEPARATION WAS LOST.

Narrative

MECHANICAL FAILURE: AFTER COMPLETING A NORMAL TKOF AND ASSOCIATED PROCS; THE L MAIN GEAR FAILED TO RESTART. INDICATIONS WERE: RED 'DOORS' LIGHT; RED 'IN-TRANSIT' LIGHT; AND AMBER 'L-HAND GEAR OR DOOR' LIGHT ILLUMINATED. ACFT WAS STABILIZED IN A CLB AT 200 KIAS AND FLAPS 4 DEGS AND A CLB TO 10000 FT MSL WAS COMPLETED. WHILE BEING VECTORED BY DEP CTL IN THE RADAR PATTERN; THE CAPT AND SO PERFORMED THE 'IN TRANSIT GEAR OR DOOR LIGHT ON AFTER RETRACTION' CHKLIST. THESE PROCS DID NOT CORRECT THE PROB AND THE PROCS DIRECTED A LNDG AT THE NEAREST SUITABLE ARPT. THE DECISION WAS MADE TO RETURN TO ATL. AFTER COMPLETING ALL OF THE MALFUNCTION CHKLISTS; THE END RESULT WAS GEAR DOWN AND LOCKED; WITH A SAFE 'GREEN' INDICATION. EMER EQUIP WAS REQUESTED TO BE AVAILABLE ON LNDG. A NORMAL APCH AND LNDG TO RWY 27R WAS ACCOMPLISHED WITH NO DIFFICULTIES (LNDG WT 355000 LBS). THE ACFT WAS RETURNED TO THE GATE. ATC CONFLICT: WHILE BEING RADAR VECTORED IN THE RADAR PATTERN; OUR POS WAS APPROX 22 DME E OF ATL. WE HAD INFORMED ATC THAT WE HAD COMPLETED OUR ANALYSIS AND TROUBLESHOOTING OF THE GEAR PROB AND WE WERE READY TO RETURN TO ATL. UP UNTIL THIS TIME; WE WERE BEING VECTORED BY DEP CTL AND THEY HAD ASSIGNED US A 330 DEG HDG TO POS US FOR A L BASE TO RWY 27R. IT WAS AT THIS TIME WE WERE HANDED OFF TO ATL APCH AND WERE UNABLE TO CHK IN DUE TO FREQ CONGESTION. THIS LAST 330 DEG HDG ASSIGNED BY DEP; APPEARED TO PUT US IN CONFLICT WITH ACFT Y ON A R BASE TO RWY 26R ON THE N COMPLEX. WE DID RECEIVE A TA ON TCASII FOLLOWED BY AN URGENT DIRECTIVE BY APCH CTL TO MAKE AN IMMEDIATE R TURN TO 090 DEGS; AT THE SAME TIME THEY DIRECTED ACFT Y TO MAKE AN IMMEDIATE TURN TO 270 DEGS. SEPARATION APPEARED TO BE MINIMAL WITH 1 - 1 1/2 MI SEPARATION -- BOTH AT 4000 FT. THE TURNS WERE COMPLETED AND LATER APCH AND LNDG WERE COMPLETED UNEVENTFULLY.