Air carrier X had less than standard separation from air carrier Y during descent through occupied altitude. System error. TCASII TA RA. Evasive action taken.

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Attributes
ACN	191741
Time
Date	199110
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ocn
State Reference	CA
Altitude	msl bound lower : 10700 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Route In Use	enroute : on vectors enroute airway : sna
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 70 flight time total : 15000 flight time type : 7000
ASRS Report	191741
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 180 flight time total : 12000 flight time type : 1350
ASRS Report	191711
Events
Anomaly	non adherence : published procedure non adherence : required legal separation
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance flight crew : took evasive action other
Consequence	faa : investigated faa : reviewed incident with flight crew
Miss Distance	horizontal : 6000 vertical : 300
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X vista 1 arrival and outbound from ocn on a radar vector we received a clearance to descend from 12000 to 10000. During the descent, while at 10700 MSL, our TCASII gave 'traffic at 1- 2 O'clock +300 ft' when I started a turn to the left when traffic went red on the radar. The controller gave a left heading change to air carrier Y at 11000 ft and we passed in close visual contact. I called coast and talked to supervisor who had already talked to the air carrier Y captain. Supervisor indicated that a system error had occurred on their part. Supplemental information from acn 191711: air carrier X on a northwest radar vector west of oceanside VOR descending for approach to lax. We were cleared to descend from 12000 ft to 10000 ft by coast approach. At 10700 ft the TCASII reported a traffic conflict 300 ft above our altitude. We continued descent and saw traffic pass off to our right at 11000 ft approximately 1 mi.

Original NASA ASRS Text

Title: ACR X HAD LTSS FROM ACR Y DURING DSCNT THROUGH OCCUPIED ALT. SYS ERROR. TCASII TA RA. EVASIVE ACTION TAKEN.

Narrative: ACR X VISTA 1 ARR AND OUTBOUND FROM OCN ON A RADAR VECTOR WE RECEIVED A CLRNC TO DSND FROM 12000 TO 10000. DURING THE DSCNT, WHILE AT 10700 MSL, OUR TCASII GAVE 'TFC AT 1- 2 O'CLOCK +300 FT' WHEN I STARTED A TURN TO THE L WHEN TFC WENT RED ON THE RADAR. THE CTLR GAVE A L HDG CHANGE TO ACR Y AT 11000 FT AND WE PASSED IN CLOSE VISUAL CONTACT. I CALLED COAST AND TALKED TO SUPVR WHO HAD ALREADY TALKED TO THE ACR Y CAPT. SUPVR INDICATED THAT A SYS ERROR HAD OCCURRED ON THEIR PART. SUPPLEMENTAL INFO FROM ACN 191711: ACR X ON A NW RADAR VECTOR W OF OCEANSIDE VOR DSNDING FOR APCH TO LAX. WE WERE CLRED TO DSND FROM 12000 FT TO 10000 FT BY COAST APCH. AT 10700 FT THE TCASII RPTED A TFC CONFLICT 300 FT ABOVE OUR ALT. WE CONTINUED DSCNT AND SAW TFC PASS OFF TO OUR R AT 11000 FT APPROX 1 MI.

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.