Narrative:

Air carrier Y was sbound at FL280. Air carrier X was nwbound at 290 requiring descent to FL190. I was busy monitoring 2 other sits involving separation and when it was time to descend X I did so -- never seeing Y at FL280. It was discovered when I started to issue communication change to X (about a min later) and saw the traffic. At that time the pilot asked about the traffic and I cleared him to maintain FL290 since his mode C indicated he had not started his descent. He had in fact begun his descent and was unable to stop it soon enough to avoid the incident. Contributing factors are that air carrier X was 20 mi east of course for no apparent reason and without coordination. Had he been on the route in the LOA there would not have been any traffic. 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 local to go home and get some rest.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.