Narrative:

I was working two sectors (sector 6 and sector 13), radar and radar associated combined. Aircraft X checked on sector 13 at FL240. This altitude was a wrong altitude for direction of flight and an approval request was not made. Aircraft Y checked on sector 13 at FL230. Aircraft Y was about 4 miles in trail. I thought I saw aircraft X at FL230 and aircraft Y at FL240. I issued a clearance to aircraft X to cross ramms at 15000 and issued the denver altimeter. Aircraft X acknowledged the clearance. Conflict alert activated shortly after aircraft X left FL240. At the time of the conflict alert, I was vectoring two denver departures and coordination with the high altitude sector for higher altitudes for both departures trying to miss an overflt at FL250. The departures were in sector 6. When I noticed aircraft Y's altitude it was FL232 and descending below aircraft Y. The aircraft were about 3.3 miles apart and not in any conflict. Twenty degrees to the right and I vectored aircraft X 20 degrees to the left. This was to try and get my sequence to denver approach by moving aircraft X to the tomsn STAR. I then cleared aircraft X to intercept the falcon 306 radial tomsn three arrival. I cleared aircraft X to cross tomsn at 17000 ft and issued the denver altimeter. I then cleared aircraft Y to a lower altitude stepping him down reference aircraft X. My misreading of the altitudes was the problem. If the approval request on aircraft X at wrong altitude for direction of flight was made this may have helped to prevent the problem. Also, not working two sectors at once and/or another controller on the sector may have helped.

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Original NASA ASRS Text

Title: LOSS OF SEPARATION OCCURRED WHEN A ZDV ARTCC RADAR CTLR DID NOT ENSURE TRAILING B190 ACR DID NOT OVERTAKE DESCENDING SAME TYPE ACFT AHEAD.

Narrative: I WAS WORKING TWO SECTORS (SECTOR 6 AND SECTOR 13), RADAR AND RADAR ASSOCIATED COMBINED. ACFT X CHKED ON SECTOR 13 AT FL240. THIS ALT WAS A WRONG ALT FOR DIRECTION OF FLT AND AN APPROVAL REQUEST WAS NOT MADE. ACFT Y CHKED ON SECTOR 13 AT FL230. ACFT Y WAS ABOUT 4 MILES IN TRAIL. I THOUGHT I SAW ACFT X AT FL230 AND ACFT Y AT FL240. I ISSUED A CLRNC TO ACFT X TO CROSS RAMMS AT 15000 AND ISSUED THE DENVER ALTIMETER. ACFT X ACKNOWLEDGED THE CLRNC. CONFLICT ALERT ACTIVATED SHORTLY AFTER ACFT X LEFT FL240. AT THE TIME OF THE CONFLICT ALERT, I WAS VECTORING TWO DENVER DEPS AND COORD WITH THE HIGH ALT SECTOR FOR HIGHER ALTS FOR BOTH DEPS TRYING TO MISS AN OVERFLT AT FL250. THE DEPS WERE IN SECTOR 6. WHEN I NOTICED ACFT Y'S ALT IT WAS FL232 AND DESCENDING BELOW ACFT Y. THE ACFT WERE ABOUT 3.3 MILES APART AND NOT IN ANY CONFLICT. TWENTY DEGS TO THE R AND I VECTORED ACFT X 20 DEGS TO THE L. THIS WAS TO TRY AND GET MY SEQUENCE TO DENVER APCH BY MOVING ACFT X TO THE TOMSN STAR. I THEN CLRED ACFT X TO INTERCEPT THE FALCON 306 RADIAL TOMSN THREE ARR. I CLRED ACFT X TO CROSS TOMSN AT 17000 FT AND ISSUED THE DENVER ALTIMETER. I THEN CLRED ACFT Y TO A LOWER ALT STEPPING HIM DOWN REF ACFT X. MY MISREADING OF THE ALTS WAS THE PROB. IF THE APPROVAL REQUEST ON ACFT X AT WRONG ALT FOR DIRECTION OF FLT WAS MADE THIS MAY HAVE HELPED TO PREVENT THE PROB. ALSO, NOT WORKING TWO SECTORS AT ONCE AND/OR ANOTHER CTLR ON THE SECTOR MAY HAVE HELPED.

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.