Air carrier X had less than standard separation from air carrier Y. System error.

Attributes
ACN	155223
Time
Date	199008
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : aqn
State Reference	TX
Altitude	msl bound lower : 5000 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dfw
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 15
ASRS Report	155223
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	other other : unspecified atc
Resolutory Action	none taken : detected after the fact
Consequence	Other
Miss Distance	horizontal : 50000
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Arrival air carrier X at 9000'. Arrival air carrier Y at 6000'. I descended air carrier Y to 5000'. I then gave air carrier Y traffic, an light transport at 12 O'clock out of 6000 for 5000'. I then descended air carrier X to 5000'. While I was doing this I was giving a position relief briefing to a trnee and instrument. I thought I gave air carrier X 7000' because that is what the developmental asked me. I thought I had and got up from position. My assumption that there would be diverging, lateral or longitudinal sep was not correct in this situation. The incident occurred 3 mins after position relief. There was no evasive action.

Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM ACR Y. SYSTEM ERROR.

Narrative: ARR ACR X AT 9000'. ARR ACR Y AT 6000'. I DSNDED ACR Y TO 5000'. I THEN GAVE ACR Y TFC, AN LTT AT 12 O'CLOCK OUT OF 6000 FOR 5000'. I THEN DSNDED ACR X TO 5000'. WHILE I WAS DOING THIS I WAS GIVING A POS RELIEF BRIEFING TO A TRNEE AND INSTR. I THOUGHT I GAVE ACR X 7000' BECAUSE THAT IS WHAT THE DEVELOPMENTAL ASKED ME. I THOUGHT I HAD AND GOT UP FROM POS. MY ASSUMPTION THAT THERE WOULD BE DIVERGING, LATERAL OR LONGITUDINAL SEP WAS NOT CORRECT IN THIS SITUATION. THE INCIDENT OCCURRED 3 MINS AFTER POS RELIEF. THERE WAS NO EVASIVE ACTION.

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.