Narrative:

I was vectoring an small aircraft to follow an small transport under the control of the south arrival controller. Believing that the small transport was at a speed of about 170 KTS. I discontinued vertical situation and prepared to turn the small aircraft in behind the small transport. After I ascertained the small transport airspeed (140 KTS), I turned the small aircraft (160 KTS) onto downwind leg to follow. By the time the turn was completed the small aircraft passed within 2 mi of the small transport. I think an automated radar system, with airspds, would have prevented this occurrence. Tpx 42 does not give airspds and the south controller was somewhat too busy to ask. In the future I will be somewhat more reluctant as far as descending to the minimum vectoring altitude is concerned. Had I waited for the small aircraft to pass the projected path of the small transport. Prior to final descent, this incident would not have happened.

Google
 

Original NASA ASRS Text

Title: LOSS OF SEPARATION BETWEEN GA-SMA AND UNK-SMT. OPERATIONAL ERROR.

Narrative: I WAS VECTORING AN SMA TO FOLLOW AN SMT UNDER THE CONTROL OF THE S ARR CTLR. BELIEVING THAT THE SMT WAS AT A SPD OF ABOUT 170 KTS. I DISCONTINUED VERT SITUATION AND PREPARED TO TURN THE SMA IN BEHIND THE SMT. AFTER I ASCERTAINED THE SMT AIRSPD (140 KTS), I TURNED THE SMA (160 KTS) ONTO DOWNWIND LEG TO FOLLOW. BY THE TIME THE TURN WAS COMPLETED THE SMA PASSED WITHIN 2 MI OF THE SMT. I THINK AN AUTOMATED RADAR SYS, WITH AIRSPDS, WOULD HAVE PREVENTED THIS OCCURRENCE. TPX 42 DOES NOT GIVE AIRSPDS AND THE S CTLR WAS SOMEWHAT TOO BUSY TO ASK. IN THE FUTURE I WILL BE SOMEWHAT MORE RELUCTANT AS FAR AS DSNDING TO THE MINIMUM VECTORING ALT IS CONCERNED. HAD I WAITED FOR THE SMA TO PASS THE PROJECTED PATH OF THE SMT. PRIOR TO FINAL DSCNT, THIS INCIDENT WOULD NOT HAVE HAPPENED.

Data retrieved from NASA's ASRS site as of August 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.