Approach controller vectoring an LR55 for sequencing behind a B737 got the aircraft too close and legal separation was lost. WX was clear and the LR55 had his traffic in sight, but the B737 did get a TCASII alert and asked the approach controller about his traffic.

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Attributes
ACN	337663
Time
Date	199606
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : dsm
State Reference	IA
Altitude	msl bound lower : 4000 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dsm tower : stl
Operator	general aviation : corporate
Make Model Name	Learjet 55
Operating Under FAR Part	Part 91
Navigation In Use	Other
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 70 flight time total : 13500 flight time type : 6000
ASRS Report	337663
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error other

Narrative:

During approach we were given several vector headings including a 270 degree turn (the long way around) to put us in trail of an air carrier B737. On the turn to downwind abeam of the B737, approach got us too close to the B737 which was on 5-6 mi final. Approach also had us at too low of an altitude (4000 ft). Approach gave us a hard turn away from the B737 and a climb to 5000 ft but it was too late and separation standards were broken. The B737's TCASII went off and the captain asked for traffic. We did call the B737 in sight but, the approach controller continued to overctl us and the whole thing got messy. We had the B737 from 5-6 NM away and could have easily turned in trail of him.

Original NASA ASRS Text

Title: APCH CTLR VECTORING AN LR55 FOR SEQUENCING BEHIND A B737 GOT THE ACFT TOO CLOSE AND LEGAL SEPARATION WAS LOST. WX WAS CLR AND THE LR55 HAD HIS TFC IN SIGHT, BUT THE B737 DID GET A TCASII ALERT AND ASKED THE APCH CTLR ABOUT HIS TFC.

Narrative: DURING APCH WE WERE GIVEN SEVERAL VECTOR HDGS INCLUDING A 270 DEG TURN (THE LONG WAY AROUND) TO PUT US IN TRAIL OF AN ACR B737. ON THE TURN TO DOWNWIND ABEAM OF THE B737, APCH GOT US TOO CLOSE TO THE B737 WHICH WAS ON 5-6 MI FINAL. APCH ALSO HAD US AT TOO LOW OF AN ALT (4000 FT). APCH GAVE US A HARD TURN AWAY FROM THE B737 AND A CLB TO 5000 FT BUT IT WAS TOO LATE AND SEPARATION STANDARDS WERE BROKEN. THE B737'S TCASII WENT OFF AND THE CAPT ASKED FOR TFC. WE DID CALL THE B737 IN SIGHT BUT, THE APCH CTLR CONTINUED TO OVERCTL US AND THE WHOLE THING GOT MESSY. WE HAD THE B737 FROM 5-6 NM AWAY AND COULD HAVE EASILY TURNED IN TRAIL OF HIM.

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.