Narrative:

Air carrier X was FL390 nwbound. Air carrier Y was FL370 sebound, X was issued a descent to FL310. When the conflict was noticed, X was at FL389 and descending. X was told to climb and maintain FL390 expeditiously and to report level. X did not respond to the first call. The call was repeated and X acknowledged and reported traffic in sight. X passed behind Y by 3.8 mi and 1100 ft. There were approximately 15 aircraft on frequency and there was an assistant controller, radar controller instructor, and a handoff controller on the position in addition to myself. Supplemental information from acn 285382: I had just plugged in on the handoff position at bae high sector and was reviewing the flight data when the radar trainee descended air carrier X to FL310 with FL370 crossing traffic. I immediately called this to his attention and he reissued an altitude of FL390 to the aircraft that he just descended. The aircraft climbed back to FL390, but not before we lost separation with air carrier Y crossing traffic. Supplemental information from acn 285372: on-the-job-training was being conducted. I was distracted briefing handoff controller who had just plugged in. Trainee did not realize aircraft were in conflict. Instructor did not catch descent clearance until too late. Corrective action was initiated too late to avoid loss of separation. Supplemental information from acn 285366: air carrier X at cruise at FL390, ZAU gave X a clearance to descend to FL310. X called out of altitude and began descent. At FL380 got a TA on TCASII 12 O'clock 1000 ft below. At same time ZAU told us to climb back to FL390, conflicting traffic. Other aircraft asked about our altitude and ATC again stated his fault. Supplemental information from acn 285811: started descent from FL390 to FL310 as assigned by center. Passing FL385, center called back and told us to climb to FL390 for traffic. I looked out the window and saw traffic below and at 1 O'clock position. Almost immediately a TCASII TA was announced 'traffic.' I pointed out traffic to other crew members as climb was initiated back to FL390.

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Original NASA ASRS Text

Title: ACR X TCASII TA DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: ACR X WAS FL390 NWBOUND. ACR Y WAS FL370 SEBOUND, X WAS ISSUED A DSCNT TO FL310. WHEN THE CONFLICT WAS NOTICED, X WAS AT FL389 AND DSNDING. X WAS TOLD TO CLB AND MAINTAIN FL390 EXPEDITIOUSLY AND TO RPT LEVEL. X DID NOT RESPOND TO THE FIRST CALL. THE CALL WAS REPEATED AND X ACKNOWLEDGED AND RPTED TFC IN SIGHT. X PASSED BEHIND Y BY 3.8 MI AND 1100 FT. THERE WERE APPROX 15 ACFT ON FREQ AND THERE WAS AN ASSISTANT CTLR, RADAR CTLR INSTRUCTOR, AND A HDOF CTLR ON THE POS IN ADDITION TO MYSELF. SUPPLEMENTAL INFO FROM ACN 285382: I HAD JUST PLUGGED IN ON THE HDOF POS AT BAE HIGH SECTOR AND WAS REVIEWING THE FLT DATA WHEN THE RADAR TRAINEE DSNDED ACR X TO FL310 WITH FL370 XING TFC. I IMMEDIATELY CALLED THIS TO HIS ATTN AND HE REISSUED AN ALT OF FL390 TO THE ACFT THAT HE JUST DSNDED. THE ACFT CLBED BACK TO FL390, BUT NOT BEFORE WE LOST SEPARATION WITH ACR Y XING TFC. SUPPLEMENTAL INFO FROM ACN 285372: ON-THE-JOB-TRAINING WAS BEING CONDUCTED. I WAS DISTRACTED BRIEFING HDOF CTLR WHO HAD JUST PLUGGED IN. TRAINEE DID NOT REALIZE ACFT WERE IN CONFLICT. INSTRUCTOR DID NOT CATCH DSCNT CLRNC UNTIL TOO LATE. CORRECTIVE ACTION WAS INITIATED TOO LATE TO AVOID LOSS OF SEPARATION. SUPPLEMENTAL INFO FROM ACN 285366: ACR X AT CRUISE AT FL390, ZAU GAVE X A CLRNC TO DSND TO FL310. X CALLED OUT OF ALT AND BEGAN DSCNT. AT FL380 GOT A TA ON TCASII 12 O'CLOCK 1000 FT BELOW. AT SAME TIME ZAU TOLD US TO CLB BACK TO FL390, CONFLICTING TFC. OTHER ACFT ASKED ABOUT OUR ALT AND ATC AGAIN STATED HIS FAULT. SUPPLEMENTAL INFO FROM ACN 285811: STARTED DSCNT FROM FL390 TO FL310 AS ASSIGNED BY CTR. PASSING FL385, CTR CALLED BACK AND TOLD US TO CLB TO FL390 FOR TFC. I LOOKED OUT THE WINDOW AND SAW TFC BELOW AND AT 1 O'CLOCK POS. ALMOST IMMEDIATELY A TCASII TA WAS ANNOUNCED 'TFC.' I POINTED OUT TFC TO OTHER CREW MEMBERS AS CLB WAS INITIATED BACK TO FL390.

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.