ACR X DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR.

Narrative

ACR Y WAS SBOUND AT FL280. ACR X WAS NWBOUND AT 290 REQUIRING DSCNT TO FL190. I WAS BUSY MONITORING 2 OTHER SITS INVOLVING SEPARATION AND WHEN IT WAS TIME TO DSND X I DID SO -- NEVER SEEING Y AT FL280. IT WAS DISCOVERED WHEN I STARTED TO ISSUE COM CHANGE TO X (ABOUT A MIN LATER) AND SAW THE TFC. AT THAT TIME THE PLT ASKED ABOUT THE TFC AND I CLRED HIM TO MAINTAIN FL290 SINCE HIS MODE C INDICATED HE HAD NOT STARTED HIS DSCNT. HE HAD IN FACT BEGUN HIS DSCNT AND WAS UNABLE TO STOP IT SOON ENOUGH TO AVOID THE INCIDENT. CONTRIBUTING FACTORS ARE THAT ACR X WAS 20 MI E OF COURSE FOR NO APPARENT REASON AND WITHOUT COORD. HAD HE BEEN ON THE RTE IN THE LOA THERE WOULD NOT HAVE BEEN ANY TFC. HOWEVER I WAS AWARE HE WAS OFF COURSE AND ALTHOUGH IT WAS A FACTOR IT CERTAINLY DID NOT CAUSE THE INCIDENT. 1 FACTOR AFFECTING QUALITY OF PERFORMANCE IS THAT MY SHIFT CHANGES EVERY DAY SO I HAVE VERY POOR SLEEP PATTERNS AND OFTEN AM VERY TIRED AT WORK. IN FACT; I HAD ALREADY REQUESTED TO TAKE ANNUAL LEAVE AT XX30 LCL TO GO HOME AND GET SOME REST.