INBOUND LGT OVERSHOT ALT AND CAME INTO CLOSE PROX WITH OUTBOUND MLG.

Narrative

LGT X INBOUND RWY 24/25 PROFILE OVER FILLMORE BUSTED HIS PROFILE ALT CLRNC OF 10000' AND PASSED DANGEROUSLY CLOSE TO A NBOUND DEP (MLG Y) CLBING TO 9000'. STANDARD SEP WAS DEFINITELY LOST. ALT SEP DETERIORATED TO AS LITTLE AS 300' AND LAT SEP 1-2 MI. THE DEP CTLR WAS THE FIRST TO CATCH THE DEVIATION AND CORRECTIVE ACTION BY BOTH THE ARR CTLR AND DEP CTLR SAVED WHAT COULD POSSIBLY HAVE BEEN A CATASTROPHIC SITUATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: THIS INCIDENT WAS PROCESSED AS A PLTDEV. THE LGT FLT CREW THOUGHT THEY WERE CLRED TO 7000'. THEY WERE ACTUALLY CLRED TO 10000'. THE OUTBND MLG WAS CLRED TO AND WAS LEVEL AT 9000' THE INBOUND LGT WENT THROUGH HIS ASSIGNED ALT TO 9200. C/A SOUNDED AND BOTH THE DEP CTLR AND APCH CTLR GAVE TFC INFO AND EVASIVE INSTRUCTIONS. THE INBOUND LGT SAID HE HAD THE MLG IN SIGHT. CLOSEST POINT OF PROX WAS 1 MI AND 200'. CTLR'S EXPERIENCE LEVEL WAS DETERMINED DURING CONVERSATION. APCH CTLR TRNING WAS IN PROGRESS WITH RPTR ACTING AS INSTR.