Narrative:

Air carrier X checked on frequency. He was eastbound on J106. I cleared him to FL330. Later I got the handoff on air carrier Y, heavy wbound on J106 at FL310. I reclred air carrier X to FL290. A little while later, air carrier X called asking if I had called him. I said no, thinking I had already gotten the acknowledgement on the altitude change. When the 2 got closer together, I called traffic for both. When they were side by side, I put air carrier X on sector 14's frequency, and saw him leave FL290 right at the end of my transmission. After listening to the tape, it was obvious I did not get the acknowledgement from air carrier X, because aircraft called asking which chicago frequency he was supposed to be on. Callback conversation with reporter revealed the following: air carrier X type aircraft: 3 engine large transport. Reporter's experience: 1 yr radar, 4 yrs non radar. Flight conditions: VMC. Time of occurrence: 2. Place: eau 20 mi east. EST miss: 700' vertical, 21000' horizontal. Reporter stated the facility processed this as a system error. Computer detected error.

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Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM ACR Y. SYSTEM ERROR.

Narrative: ACR X CHKED ON FREQ. HE WAS EBND ON J106. I CLRED HIM TO FL330. LATER I GOT THE HDOF ON ACR Y, HVY WBOUND ON J106 AT FL310. I RECLRED ACR X TO FL290. A LITTLE WHILE LATER, ACR X CALLED ASKING IF I HAD CALLED HIM. I SAID NO, THINKING I HAD ALREADY GOTTEN THE ACKNOWLEDGEMENT ON THE ALT CHANGE. WHEN THE 2 GOT CLOSER TOGETHER, I CALLED TFC FOR BOTH. WHEN THEY WERE SIDE BY SIDE, I PUT ACR X ON SECTOR 14'S FREQ, AND SAW HIM LEAVE FL290 RIGHT AT THE END OF MY XMISSION. AFTER LISTENING TO THE TAPE, IT WAS OBVIOUS I DID NOT GET THE ACKNOWLEDGEMENT FROM ACR X, BECAUSE ACFT CALLED ASKING WHICH CHICAGO FREQ HE WAS SUPPOSED TO BE ON. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: ACR X TYPE ACFT: 3 ENG LGT. RPTR'S EXPERIENCE: 1 YR RADAR, 4 YRS NON RADAR. FLT CONDITIONS: VMC. TIME OF OCCURRENCE: 2. PLACE: EAU 20 MI E. EST MISS: 700' VERT, 21000' HORIZ. RPTR STATED THE FAC PROCESSED THIS AS A SYS ERROR. COMPUTER DETECTED ERROR.

Data retrieved from NASA's ASRS site as of August 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.