Narrative:

I was working at the low altitude sector in the roanoke, va area. Took a handoff from roa approach on an air carrier medium large transport filed for FL240 from roa V260 rnl -- ord. On initial contact with medium large transport, I climbed medium large transport to FL230. About this time, I took a handoff from ZID on an small transport, flight plan rac -- roa. At FL230 descending to 11000, the aircraft are on opposite courses. Considering the performance of both aircraft, I decided to leave both aircraft on their opposite direction courses and monitor their progress so I could take an alternate course of action if it became necessary. At this time, I was moderately busy with other traffic in the sector. During the next few mins, my workload increased considerably and my attention was diverted from this climbing descending situation. About 4 or 6 mins later, I noticed that the 2 aircraft are about 10 or 12 mi apart, head-on, and the small transport is still too far above the medium large transport for them to pass with sufficient vertical or horizontal separation. In fact, it looked like they might collide if I didnþt take immediate action. According to mode C information, the small transport was still above FL180 and the medium large transport out of 16000 still climbing. I tell the small transport to maintain FL180 and turn left immediately to a heading of 090 degree. The small transport acknowledges the turn and says weþll climb back up to FL180. By this time, the conflict alert is flashing and the medium large transport shows through 17000. I figure by this time to stop the medium large transport climb wouldnþt help the situation and would only take more time in a clearance, so I tell the medium large transport to turn left heading 270 degrees immediately. The 2 aircraft pass 4.3 mi horizontally and 200 ft separation. As soon as both aircraft are clear of each other, I clear them back on course. As revealed by investigating the radar computer data, if I had taken no action, the aircraft would have passed with more than the required separation min. I hadnþt fully taken into account the lag in the mode C readout when high performance aircraft are climbing or descending. My first reaction to the situation as I saw it was that I had to do something quick to avert a possible disaster. As it turned out, my judgement was grievously in error. I should have monitored this situation closer so as to ensure separation from the very first clearance.

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Original NASA ASRS Text

Title: ATC RADAR CTLR BECAME DISTR AND ALLOWED LTSS IN A CLB AND DSCNT SITUATION. VECTOR TURNS PREVENTED A SERIOUS SITUATION TO DEVELOP FURTHER.

Narrative: I WAS WORKING AT THE LOW ALT SECTOR IN THE ROANOKE, VA AREA. TOOK A HDOF FROM ROA APCH ON AN ACR MLG FILED FOR FL240 FROM ROA V260 RNL -- ORD. ON INITIAL CONTACT WITH MLG, I CLBED MLG TO FL230. ABOUT THIS TIME, I TOOK A HDOF FROM ZID ON AN SMT, FLT PLAN RAC -- ROA. AT FL230 DSNDING TO 11000, THE ACFT ARE ON OPPOSITE COURSES. CONSIDERING THE PERFORMANCE OF BOTH ACFT, I DECIDED TO LEAVE BOTH ACFT ON THEIR OPPOSITE DIRECTION COURSES AND MONITOR THEIR PROGRESS SO I COULD TAKE AN ALTERNATE COURSE OF ACTION IF IT BECAME NECESSARY. AT THIS TIME, I WAS MODERATELY BUSY WITH OTHER TFC IN THE SECTOR. DURING THE NEXT FEW MINS, MY WORKLOAD INCREASED CONSIDERABLY AND MY ATTN WAS DIVERTED FROM THIS CLBING DSNDING SITUATION. ABOUT 4 OR 6 MINS LATER, I NOTICED THAT THE 2 ACFT ARE ABOUT 10 OR 12 MI APART, HEAD-ON, AND THE SMT IS STILL TOO FAR ABOVE THE MLG FOR THEM TO PASS WITH SUFFICIENT VERT OR HORIZ SEPARATION. IN FACT, IT LOOKED LIKE THEY MIGHT COLLIDE IF I DIDNþT TAKE IMMEDIATE ACTION. ACCORDING TO MODE C INFO, THE SMT WAS STILL ABOVE FL180 AND THE MLG OUT OF 16000 STILL CLBING. I TELL THE SMT TO MAINTAIN FL180 AND TURN L IMMEDIATELY TO A HDG OF 090 DEG. THE SMT ACKNOWLEDGES THE TURN AND SAYS WEþLL CLB BACK UP TO FL180. BY THIS TIME, THE CONFLICT ALERT IS FLASHING AND THE MLG SHOWS THROUGH 17000. I FIGURE BY THIS TIME TO STOP THE MLG CLB WOULDNþT HELP THE SITUATION AND WOULD ONLY TAKE MORE TIME IN A CLRNC, SO I TELL THE MLG TO TURN L HDG 270 DEGS IMMEDIATELY. THE 2 ACFT PASS 4.3 MI HORIZLY AND 200 FT SEPARATION. AS SOON AS BOTH ACFT ARE CLR OF EACH OTHER, I CLR THEM BACK ON COURSE. AS REVEALED BY INVESTIGATING THE RADAR COMPUTER DATA, IF I HAD TAKEN NO ACTION, THE ACFT WOULD HAVE PASSED WITH MORE THAN THE REQUIRED SEPARATION MIN. I HADNþT FULLY TAKEN INTO ACCOUNT THE LAG IN THE MODE C READOUT WHEN HIGH PERFORMANCE ACFT ARE CLBING OR DSNDING. MY FIRST REACTION TO THE SITUATION AS I SAW IT WAS THAT I HAD TO DO SOMETHING QUICK TO AVERT A POSSIBLE DISASTER. AS IT TURNED OUT, MY JUDGEMENT WAS GRIEVOUSLY IN ERROR. I SHOULD HAVE MONITORED THIS SITUATION CLOSER SO AS TO ENSURE SEPARATION FROM THE VERY FIRST CLRNC.

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.