Narrative:

Air carrier X was east southeast bound from the west at FL390. Aircraft Y was southeast bound from the northwest at FL390. I realized early on that both aircraft were converging; at least 10 minutes prior to the event; but at this time did not check the trajectories in the uret (user request evaluation tool) though I did notice I was showing no alerts. I issued aircraft X a clearance direct kelpp which turned him slightly right; thinking that would probably help with any conflict resolution in the future; planning on eventually taking him behind air carrier X if necessary as he was much slower. Now I probed aircraft Y in uret and he was red with air carrier X at about 10 miles inside the next sector (23). I asked each pilot in turn if they could accept FL410 but both said they were too heavy. I then determined I was going to vector and kept running the vectors out. It appeared they were almost tied at 8 minutes to go and air carrier X was much faster by at least 100 knots. All my experience and intuition was telling me I needed to turn the citation behind the air carrier X; and even so it was going to take a healthy turn of due south; but because of the angles; for some reason I wasn't comfortable turning the citation into the air carrier X and instead decided with about 5 minutes to go to turn the air carrier X instead. I issued a heading of 075 for traffic; about a 40 degree left turn. The pilot acknowledged but made a very slow turn. I pointed the air carrier X out to an adjacent sector to the east and as I was doing so the conflict alert activated. I realized the turn was not going to be enough and turned the air carrier X further left to 045. As they continued to turn; I knew it was going to be very close to a loss of separation and issued a descent to the air carrier X to FL380. The pilot acknowledged the clearance and after I got 3 updates still at FL390 I asked the pilot to descend to reach FL380 in 30 seconds or less and to report reaching; even though at this point I knew it probably wouldn't be enough to achieve vertical separation if I needed it. He stated something to the effect that company policy prohibited excessive maneuvers; blah; blah; and that he had the traffic in sight. I stated that yes the traffic was at 12 o'clock and about 5 miles. He said it looked like I had turned him right into it and I said he was going to pass behind him now. The supervisor was behind me at this point and asked me if I got a report and I said no. The qap did not activate. He went to the falcon and told me I had 5.07 miles lateral and 100 feet vertical at the closest point. I could have descended either aircraft a thousand feet temporarily and avoided the whole mess. Barring that; I should have gone with my initial instincts and turned the citation behind the air carrier X instead. Not only was he much slower but it would have turned him into a 100 knot west wind and slowed him even further. It's almost never a good idea to turn much faster traffic behind slower; and I know that.

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Original NASA ASRS Text

Title: ZHU Controller experienced a very close loss of separation event between two converging aircraft at FL390 when failing to issue timely corrective turns or altitude changes.

Narrative: Air Carrier X was east southeast bound from the west at FL390. Aircraft Y was southeast bound from the northwest at FL390. I realized early on that both aircraft were converging; at least 10 minutes prior to the event; but at this time did not check the trajectories in the URET (user request evaluation tool) though I did notice I was showing no alerts. I issued Aircraft X a clearance direct KELPP which turned him slightly right; thinking that would probably help with any conflict resolution in the future; planning on eventually taking him behind Air Carrier X if necessary as he was much slower. Now I probed Aircraft Y in URET and he was red with Air Carrier X at about 10 miles inside the next Sector (23). I asked each pilot in turn if they could accept FL410 but both said they were too heavy. I then determined I was going to vector and kept running the vectors out. It appeared they were almost tied at 8 minutes to go and Air Carrier X was much faster by at least 100 knots. All my experience and intuition was telling me I needed to turn the Citation behind the Air Carrier X; and even so it was going to take a healthy turn of due south; but because of the angles; for some reason I wasn't comfortable turning the Citation into the Air Carrier X and instead decided with about 5 minutes to go to turn the Air Carrier X instead. I issued a heading of 075 for traffic; about a 40 degree left turn. The pilot acknowledged but made a very slow turn. I pointed the Air Carrier X out to an adjacent sector to the East and as I was doing so the conflict alert activated. I realized the turn was not going to be enough and turned the Air Carrier X further left to 045. As they continued to turn; I knew it was going to be very close to a loss of separation and issued a descent to the Air Carrier X to FL380. The pilot acknowledged the clearance and after I got 3 updates still at FL390 I asked the pilot to descend to reach FL380 in 30 seconds or less and to report reaching; even though at this point I knew it probably wouldn't be enough to achieve vertical separation if I needed it. He stated something to the effect that company policy prohibited excessive maneuvers; blah; blah; and that he had the traffic in sight. I stated that yes the traffic was at 12 o'clock and about 5 miles. He said it looked like I had turned him right into it and I said he was going to pass behind him now. The supervisor was behind me at this point and asked me if I got a report and I said no. The QAP did not activate. He went to the Falcon and told me I had 5.07 miles lateral and 100 feet vertical at the closest point. I could have descended either aircraft a thousand feet temporarily and avoided the whole mess. Barring that; I should have gone with my initial instincts and turned the Citation behind the Air Carrier X instead. Not only was he much slower but it would have turned him into a 100 knot west wind and slowed him even further. It's almost never a good idea to turn much faster traffic behind slower; and I KNOW that.

Data retrieved from NASA's ASRS site as of April 2012 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.