Controller descended an aircraft so that they had less than legal separation.

Attributes
ACN	421212
Time
Date	199811
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : las
State Reference	NV
Altitude	msl bound lower : 6000 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Experience	controller military : 4 controller radar : 16 controller supervisory : 7
ASRS Report	421212
Person 2
Function	flight crew : single pilot
Qualification	pilot : instrument
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : far non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact other
Consequence	faa : investigated
Miss Distance	horizontal : 11040 vertical : 400
Supplementary
Air Traffic Incident	Operational Error

Narrative:

I was working west arrival and canyon sector combined. During the time of the event, I had 6 aircraft on frequency (4 IFR and 2 VFR). I had also taken pointouts on 2 aircraft. I was vectoring xa and xb from the south for a visual approach to runway 19R. Approximately 5 mi in trail and faster, I was vectoring xc and xd for a visual approach to runway 25L. I was also working opposite direction traffic outbound climbing to 13000 ft, and traffic from the west, a B737 that I was sequencing to runway 25L downwind behind xc. I descended xa to 6000 ft. When I observed xa leave 7000 ft, I instructed xc to descend and maintain 6000 ft. My intentions were to descend xc to 8000 ft. In my mind I had descended xc to 8000 ft and didn't realize I had actually descended xc to 6000 ft until listening to tape after incident. I then focused on B737 traffic from the west. Made a turn and traffic call. I terminated a navajo outside of class B. I observed xc descending through 6700 ft. I turned xc right to heading 080 degrees to regain standard IFR separation. I reported to supervisor.

Original NASA ASRS Text

Title: CTLR DSNDED AN ACFT SO THAT THEY HAD LESS THAN LEGAL SEPARATION.

Narrative: I WAS WORKING W ARR AND CANYON SECTOR COMBINED. DURING THE TIME OF THE EVENT, I HAD 6 ACFT ON FREQ (4 IFR AND 2 VFR). I HAD ALSO TAKEN POINTOUTS ON 2 ACFT. I WAS VECTORING XA AND XB FROM THE S FOR A VISUAL APCH TO RWY 19R. APPROX 5 MI IN TRAIL AND FASTER, I WAS VECTORING XC AND XD FOR A VISUAL APCH TO RWY 25L. I WAS ALSO WORKING OPPOSITE DIRECTION TFC OUTBOUND CLBING TO 13000 FT, AND TFC FROM THE W, A B737 THAT I WAS SEQUENCING TO RWY 25L DOWNWIND BEHIND XC. I DSNDED XA TO 6000 FT. WHEN I OBSERVED XA LEAVE 7000 FT, I INSTRUCTED XC TO DSND AND MAINTAIN 6000 FT. MY INTENTIONS WERE TO DSND XC TO 8000 FT. IN MY MIND I HAD DSNDED XC TO 8000 FT AND DIDN'T REALIZE I HAD ACTUALLY DSNDED XC TO 6000 FT UNTIL LISTENING TO TAPE AFTER INCIDENT. I THEN FOCUSED ON B737 TFC FROM THE W. MADE A TURN AND TFC CALL. I TERMINATED A NAVAJO OUTSIDE OF CLASS B. I OBSERVED XC DSNDING THROUGH 6700 FT. I TURNED XC R TO HDG 080 DEGS TO REGAIN STANDARD IFR SEPARATION. I RPTED TO SUPVR.

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.