Loss of separation between GA-small aircraft and unk-small transport. Operational error.

Attributes
ACN	103801
Time
Date	198902
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : lan
State Reference	MI
Altitude	msl bound lower : 2800 msl bound upper : 2800
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : lan
Operator	general aviation : corporate
Make Model Name	Small Aircraft, Low Wing, 2 Eng, Retractable Gear
Flight Phase	descent : approach descent other
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent : approach
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	103801
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	conflict : airborne less severe non adherence : far non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

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.

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.