Approach controller vectored an aircraft behind another aircraft and lost lateral radar separation.

Attributes
ACN	154256
Time
Date	199008
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : gpt
State Reference	MS
Altitude	msl bound lower : 1000 msl bound upper : 1700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : gpt tower : bdr
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach descent other
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Fighter
Flight Phase	other
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller military : 7 controller radar : 9
ASRS Report	154256
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	none taken : anomaly accepted
Consequence	faa : investigated
Miss Distance	horizontal : 16800 vertical : 700
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

The problem arose while I was working the west radar sector in 8/90. Traffic consisted of numerous aircraft (IFR) on vectors to the 360 degree overhead pattern and an small transport aircraft (IFR) making multiple practice approachs. Reference the fgt being vectored to the 360 degree overhead pattern and the small transport inbound on the ILS runway 13 approach, I vectored the fgt to follow the small transport on final. Applying course divergence procedures, I vectored the fgt toward a point behind the small transport. At the point where the fgt was turned toward the small transport. I had at least 5 mi latitude sep and the fgt on a course which crossed behind the small transport. The fgt was level at 1700' and the small transport was descending out of 1000' on the approach. The fgt's flight came within 2-3 mi latitude and behind (5 O'clock) the small transport on a diverging course away from the small transport. After observing that the sequence to the runway would not work due to aircraft characteristics, the fgt would overtake the small transport if turned inbound, I turned the fgt away from the airport in order to achieve the desired sequence to the runway. My perception and judgement consisted of the fact that the small transport had already crossed the projected flight path of the fgt, the fgt would pass 2-3 mi behind the small transport on a diverging course away from the small transport. The small transport was descending on the ILS approach and the fgt was in level flight, and there was no way the 2 aircraft could conflict with each other. Based on these perceptions and my interpretation of the diverging course sep rule, no action was taken to increase the sep to 3 mi behind the small transport. The above situation was reported to the air traffic manager by the local controller as 2 aircraft converging on each other at the same altitude with less than 3 mi latitude sep. ARTS 11 magnetic data extraction definitely supports the fact the 2 aircraft were on diverging courses at all times and the fact the aircraft had less than 3 mi latitude sep and less than 1000'.

Original NASA ASRS Text

Title: APCH CTLR VECTORED AN ACFT BEHIND ANOTHER ACFT AND LOST LATERAL RADAR SEPARATION.

Narrative: THE PROB AROSE WHILE I WAS WORKING THE W RADAR SECTOR IN 8/90. TFC CONSISTED OF NUMEROUS ACFT (IFR) ON VECTORS TO THE 360 DEG OVERHEAD PATTERN AND AN SMT ACFT (IFR) MAKING MULTIPLE PRACTICE APCHS. REF THE FGT BEING VECTORED TO THE 360 DEG OVERHEAD PATTERN AND THE SMT INBND ON THE ILS RWY 13 APCH, I VECTORED THE FGT TO FOLLOW THE SMT ON FINAL. APPLYING COURSE DIVERGENCE PROCS, I VECTORED THE FGT TOWARD A POINT BEHIND THE SMT. AT THE POINT WHERE THE FGT WAS TURNED TOWARD THE SMT. I HAD AT LEAST 5 MI LAT SEP AND THE FGT ON A COURSE WHICH CROSSED BEHIND THE SMT. THE FGT WAS LEVEL AT 1700' AND THE SMT WAS DSNDING OUT OF 1000' ON THE APCH. THE FGT'S FLT CAME WITHIN 2-3 MI LAT AND BEHIND (5 O'CLOCK) THE SMT ON A DIVERGING COURSE AWAY FROM THE SMT. AFTER OBSERVING THAT THE SEQUENCE TO THE RWY WOULD NOT WORK DUE TO ACFT CHARACTERISTICS, THE FGT WOULD OVERTAKE THE SMT IF TURNED INBND, I TURNED THE FGT AWAY FROM THE ARPT IN ORDER TO ACHIEVE THE DESIRED SEQUENCE TO THE RWY. MY PERCEPTION AND JUDGEMENT CONSISTED OF THE FACT THAT THE SMT HAD ALREADY CROSSED THE PROJECTED FLT PATH OF THE FGT, THE FGT WOULD PASS 2-3 MI BEHIND THE SMT ON A DIVERGING COURSE AWAY FROM THE SMT. THE SMT WAS DSNDING ON THE ILS APCH AND THE FGT WAS IN LEVEL FLT, AND THERE WAS NO WAY THE 2 ACFT COULD CONFLICT WITH EACH OTHER. BASED ON THESE PERCEPTIONS AND MY INTERP OF THE DIVERGING COURSE SEP RULE, NO ACTION WAS TAKEN TO INCREASE THE SEP TO 3 MI BEHIND THE SMT. THE ABOVE SITUATION WAS RPTED TO THE AIR TFC MGR BY THE LCL CTLR AS 2 ACFT CONVERGING ON EACH OTHER AT THE SAME ALT WITH LESS THAN 3 MI LAT SEP. ARTS 11 MAGNETIC DATA EXTRACTION DEFINITELY SUPPORTS THE FACT THE 2 ACFT WERE ON DIVERGING COURSES AT ALL TIMES AND THE FACT THE ACFT HAD LESS THAN 3 MI LAT SEP AND LESS THAN 1000'.

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.