Narrative:

The king air (aircraft X) was eastbound toward lft at FL230. Air carrier Y was descending to FL240. When air carrier Y checked on, I used the range lines to check distance in 2-4 mins. I thought air carrier Y was descending at a rate which would clear the king air. I gave him further descent to 17000 ft. I went on to other control functions. When I looked back, I realized he would not clear the king air. I turned the king air 15 degrees left and turned air carrier Y 30 degrees and told him to expedite through FL220. I felt this was enough to maintain separation. When the air carrier reported out of FL220, he was 4 mi from the king air. The king air reported the air carrier in sight, but visual separation cannot be used above FL180. The error detection patch logged the closest point at 4 mi and 600 ft.

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Original NASA ASRS Text

Title: ZHU CTLR PROJECTS 'RANGE LINE' TO ANTICIPATE PROPOSED SEPARATION. SEPARATION DID NOT MATERIALIZE AND LAST MIN VECTOR ATTEMPTS CANNOT MAINTAIN REQUIRED SEPARATION.

Narrative: THE KING AIR (ACFT X) WAS EBOUND TOWARD LFT AT FL230. ACR Y WAS DSNDING TO FL240. WHEN ACR Y CHKED ON, I USED THE RANGE LINES TO CHK DISTANCE IN 2-4 MINS. I THOUGHT ACR Y WAS DSNDING AT A RATE WHICH WOULD CLR THE KING AIR. I GAVE HIM FURTHER DSCNT TO 17000 FT. I WENT ON TO OTHER CTL FUNCTIONS. WHEN I LOOKED BACK, I REALIZED HE WOULD NOT CLR THE KING AIR. I TURNED THE KING AIR 15 DEGS L AND TURNED ACR Y 30 DEGS AND TOLD HIM TO EXPEDITE THROUGH FL220. I FELT THIS WAS ENOUGH TO MAINTAIN SEPARATION. WHEN THE ACR RPTED OUT OF FL220, HE WAS 4 MI FROM THE KING AIR. THE KING AIR RPTED THE ACR IN SIGHT, BUT VISUAL SEPARATION CANNOT BE USED ABOVE FL180. THE ERROR DETECTION PATCH LOGGED THE CLOSEST POINT AT 4 MI AND 600 FT.

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.