Narrative:

An air taxi to SF34 departed the airport heading 280 degrees. About 5 mi west of the airport, I turned the aircraft to 315 degrees to gain the required in-trail separation with a preceding departure. 2 departures later, an md-80 departed the same runway heading 260 degrees, as required for noise abatement. When the md-80 was out of 3600 ft MSL, I turned to him to 320 degrees, which was about on-course. When the md-80 was about 5-6 mi behind the SF34, with both climbing out, I turned the SF34 left to 245 degrees to intercept his on-course, expecting this to provide diverging-course separation from the md-80, which was overtaking the SF34 by about 100 KTS. When the aircraft were about 4 mi apart, I issued traffic to the md-80, and he responded insight. 2 xmissions later, I issued traffic to the SF34 as passing behind and to your left. He also responded in sight and that he had received an RA from his TCASII. At this point, the md-80 questioned the operation advising the SF34 had been right in front of him and he responded to a descent RA from his TCASII in order to avoid a conflict. All the while, I felt that while the aircraft did get closer than I anticipated, I had legally separated them with course divergence. After being advised by the md-80's company of the captain's desire to file a near midair collision report, we generated a computer plot of the 2 aircraft's relative position during the operation. It was at this time I found that, when I thought the 2 aircraft were directly in-trail and I was turning the SF34 out of the way of the md-80, the SF34 was, in reality, slightly to the right of the md-80, such that when I turned him left, I had actually turned him into the md-80's path instead of away from it. The nearest proximity prior to divergence was about 500 ft and 1.8 mi.

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Original NASA ASRS Text

Title: MD-80 TCASII RA HAD LTSS FROM ACR X. SYS ERROR. EVASIVE ACTION TAKEN.

Narrative: AN AIR TAXI TO SF34 DEPARTED THE ARPT HDG 280 DEGS. ABOUT 5 MI W OF THE ARPT, I TURNED THE ACFT TO 315 DEGS TO GAIN THE REQUIRED IN-TRAIL SEPARATION WITH A PRECEDING DEP. 2 DEPS LATER, AN MD-80 DEPARTED THE SAME RWY HDG 260 DEGS, AS REQUIRED FOR NOISE ABATEMENT. WHEN THE MD-80 WAS OUT OF 3600 FT MSL, I TURNED TO HIM TO 320 DEGS, WHICH WAS ABOUT ON-COURSE. WHEN THE MD-80 WAS ABOUT 5-6 MI BEHIND THE SF34, WITH BOTH CLBING OUT, I TURNED THE SF34 L TO 245 DEGS TO INTERCEPT HIS ON-COURSE, EXPECTING THIS TO PROVIDE DIVERGING-COURSE SEPARATION FROM THE MD-80, WHICH WAS OVERTAKING THE SF34 BY ABOUT 100 KTS. WHEN THE ACFT WERE ABOUT 4 MI APART, I ISSUED TFC TO THE MD-80, AND HE RESPONDED INSIGHT. 2 XMISSIONS LATER, I ISSUED TFC TO THE SF34 AS PASSING BEHIND AND TO YOUR L. HE ALSO RESPONDED IN SIGHT AND THAT HE HAD RECEIVED AN RA FROM HIS TCASII. AT THIS POINT, THE MD-80 QUESTIONED THE OP ADVISING THE SF34 HAD BEEN RIGHT IN FRONT OF HIM AND HE RESPONDED TO A DSCNT RA FROM HIS TCASII IN ORDER TO AVOID A CONFLICT. ALL THE WHILE, I FELT THAT WHILE THE ACFT DID GET CLOSER THAN I ANTICIPATED, I HAD LEGALLY SEPARATED THEM WITH COURSE DIVERGENCE. AFTER BEING ADVISED BY THE MD-80'S COMPANY OF THE CAPT'S DESIRE TO FILE A NMAC RPT, WE GENERATED A COMPUTER PLOT OF THE 2 ACFT'S RELATIVE POS DURING THE OP. IT WAS AT THIS TIME I FOUND THAT, WHEN I THOUGHT THE 2 ACFT WERE DIRECTLY IN-TRAIL AND I WAS TURNING THE SF34 OUT OF THE WAY OF THE MD-80, THE SF34 WAS, IN REALITY, SLIGHTLY TO THE R OF THE MD-80, SUCH THAT WHEN I TURNED HIM L, I HAD ACTUALLY TURNED HIM INTO THE MD-80'S PATH INSTEAD OF AWAY FROM IT. THE NEAREST PROX PRIOR TO DIVERGENCE WAS ABOUT 500 FT AND 1.8 MI.

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.