MEM APCH CTLR DESCRIBED CONFLICT WHILE WORKING FINAL MONITOR POS WHEN ACFT MISSED LOC INTERCEPT AND CONFLICTED WITH PARALLEL TFC.

Narrative

I WAS WORKING FINAL MONITOR W AT MEM; I DID THE FREQ OVER RIDE CHK. I NOTIFIED LCL THAT FINAL MONITORING WAS IN PROGRESS AND DETERMINED HOW FAR OUT TFC WAS VISIBLE. LCL SAID 2 - 2 1/2 MI. LCL ASKED ABOUT CALLING THE APCH FIXES BECAUSE THE DME ON THE RWY 36L LOC WAS OTS. FINAL MONITOR E COMMENTED THAT THE WX SEQUENCE ON THE IDS SCREEN WAS NOT CURRENT. HE/SHE MOVED DOWN TO THE NEXT POS (ABOUT 3 FT) TO CHK THE CURRENT WX AND I MONITORED THE ATIS; TO DETERMINE THE CURRENT WX AND TO VERIFY THAT THE DME OTS WAS BROADCAST CORRECTLY. ACFT X WAS ESTABLISHED ON THE RWY 36L LOC XING THE STEP-DOWN FIX AT 4000 FT WHILE ACFT Y WAS ON THE BASE FOR THE E PARALLEL ABOUT 2 MI BEHIND ACFT X AT 3000 FT. ALL IS WELL. I MOVE ON WITH MY SCAN. A FEW SECONDS LATER; FME POINTS TO ACFT X AND TELLS ME TO STOP THEM AT 4000 FT. I LOOK AT ACFT X AND HE IS DSNDING OUT OF 3700 FT STILL ON THE LOC AND ACFT Y IS ABOUT 2 MI BEHIND ON A NE HDG. ACFT Y APPARENTLY WENT THROUGH THE LOC AND WAS CORRECTING. I TOLD FME THAT THEY HAD DIVERGING COURSES. PROCS REQUIRE THAT ACFT ARE ESTABLISHED ON THE FINAL AND ON TWR FREQ OUTSIDE OF THE W STEP-DOWN FIX; W RWY AT 4000 FT; E RWY AT 3000 FT. ACFT Y WENT THROUGH THE LOC AND JOINED 2 MI INSIDE THE E STEP-DOWN FIX. THE E STEP-DOWN FIX IS APPROX 1 MI INSIDE THE W STEP-DOWN FIX. I DON'T SEE HOW I COULD HAVE PREVENTED THIS ERROR AND I CERTAINLY DID NOTHING TO CAUSE IT.