Narrative:

I was working sector 28 radar associate position for approximately 15 mins. There was light to moderate traffic and light chop occasionally being reported. The radar controller issued a descent clearance to FL270 on an air carrier X arrival at FL360. As the radar controller was giving the clearance; I pointed to an air carrier Y overflt at FL350 on the scope. In my opinion there was insufficient room for air carrier X to descend below air carrier Y. The radar controller then instructed air carrier X flight to maintain at least 2000 FPM in the descent. After 3 radar hits; air carrier X flight still showed level at FL360. The radar controller asked air carrier X if he had started descending yet and the pilot replied affirmative. The radar controller issued a 30 degree left turn to air carrier X flight and a 50 degree left turn to air carrier Y. In addition; air carrier X flight was instructed to climb back to FL360 and air carrier Y to descend to FL340. Separation was lost. I feel that there were no out of the ordinary distrs in the area that day. In my opinion this error could have been avoided if the radar controller had used better judgement and not issued the descent clearance; or had instructed air carrier X flight to climb back to FL360 sooner. I also feel that a more expeditious descent from air carrier X would have been possible and would have avoided this loss of separation.

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Original NASA ASRS Text

Title: ZDV CTLR EXPERIENCED OPERROR AT FL350 DURING DSCNT OF ACFT THROUGH OCCUPIED ALT.

Narrative: I WAS WORKING SECTOR 28 RADAR ASSOCIATE POS FOR APPROX 15 MINS. THERE WAS LIGHT TO MODERATE TFC AND LIGHT CHOP OCCASIONALLY BEING RPTED. THE RADAR CTLR ISSUED A DSCNT CLRNC TO FL270 ON AN ACR X ARR AT FL360. AS THE RADAR CTLR WAS GIVING THE CLRNC; I POINTED TO AN ACR Y OVERFLT AT FL350 ON THE SCOPE. IN MY OPINION THERE WAS INSUFFICIENT ROOM FOR ACR X TO DSND BELOW ACR Y. THE RADAR CTLR THEN INSTRUCTED ACR X FLT TO MAINTAIN AT LEAST 2000 FPM IN THE DSCNT. AFTER 3 RADAR HITS; ACR X FLT STILL SHOWED LEVEL AT FL360. THE RADAR CTLR ASKED ACR X IF HE HAD STARTED DSNDING YET AND THE PLT REPLIED AFFIRMATIVE. THE RADAR CTLR ISSUED A 30 DEG L TURN TO ACR X FLT AND A 50 DEG L TURN TO ACR Y. IN ADDITION; ACR X FLT WAS INSTRUCTED TO CLB BACK TO FL360 AND ACR Y TO DSND TO FL340. SEPARATION WAS LOST. I FEEL THAT THERE WERE NO OUT OF THE ORDINARY DISTRS IN THE AREA THAT DAY. IN MY OPINION THIS ERROR COULD HAVE BEEN AVOIDED IF THE RADAR CTLR HAD USED BETTER JUDGEMENT AND NOT ISSUED THE DSCNT CLRNC; OR HAD INSTRUCTED ACR X FLT TO CLB BACK TO FL360 SOONER. I ALSO FEEL THAT A MORE EXPEDITIOUS DSCNT FROM ACR X WOULD HAVE BEEN POSSIBLE AND WOULD HAVE AVOIDED THIS LOSS OF SEPARATION.

Data retrieved from NASA's ASRS site as of January 2009 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.