An A320 approaching las experienced an RA with TCAS detected VFR traffic that ATC had no transponder...

Attributes
ACN	689149
Time
Date	200603
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : bld.vortac
State Reference	NV
Altitude	msl bound lower : 10000 msl bound upper : 11000
Aircraft 1
Controlling Facilities	tracon : l30.tracon
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : l30.tracon
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 240 flight time total : 8000 flight time type : 3500
ASRS Report	689149
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : airborne critical conflict : nmac
Independent Detector	aircraft equipment : tcas
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	ATC Human Performance Airspace Structure Flight Crew Human Performance
Primary Problem	ATC Human Performance

Narrative:

This is an near midair collision. While being vectored into las vegas on frequency 125.6; we were on a descent to 10000 ft 30 mi west of the bld fix. TCAS indicated 'traffic; traffic' at 900 ft below us and approximately 3 mi left of aircraft. As we started to level off through 11000 ft to 10000 ft; TCAS indicated traffic was rapidly closing our altitude and position. This seem to all happen within 30 seconds. Autoplt was on until we leveled off at 10000 ft and TCAS converted into an RA and directed us to climb. Only then did we see traffic at our 11 O'clock position within 350 ft and closing of our altitude traveling southeast to northwest. I estimate we cleared traffic by 350 ft or less vertical separation as traffic passed underneath us. I informed ATC about the incident. They replied that they held no transponder on this aircraft and never saw him. In my opinion; since we never saw the aircraft until we were in an RA; TCAS was instrumental in reporting and helping prevent this midair. Please log this event as an near midair collision.

Original NASA ASRS Text

Title: AN A320 APCHING LAS EXPERIENCED AN RA WITH TCAS DETECTED VFR TFC THAT ATC HAD NO XPONDER FOR.

Narrative: THIS IS AN NMAC. WHILE BEING VECTORED INTO LAS VEGAS ON FREQ 125.6; WE WERE ON A DSCNT TO 10000 FT 30 MI W OF THE BLD FIX. TCAS INDICATED 'TFC; TFC' AT 900 FT BELOW US AND APPROX 3 MI L OF ACFT. AS WE STARTED TO LEVEL OFF THROUGH 11000 FT TO 10000 FT; TCAS INDICATED TFC WAS RAPIDLY CLOSING OUR ALT AND POS. THIS SEEM TO ALL HAPPEN WITHIN 30 SECONDS. AUTOPLT WAS ON UNTIL WE LEVELED OFF AT 10000 FT AND TCAS CONVERTED INTO AN RA AND DIRECTED US TO CLB. ONLY THEN DID WE SEE TFC AT OUR 11 O'CLOCK POS WITHIN 350 FT AND CLOSING OF OUR ALT TRAVELING SE TO NW. I ESTIMATE WE CLRED TFC BY 350 FT OR LESS VERT SEPARATION AS TFC PASSED UNDERNEATH US. I INFORMED ATC ABOUT THE INCIDENT. THEY REPLIED THAT THEY HELD NO XPONDER ON THIS ACFT AND NEVER SAW HIM. IN MY OPINION; SINCE WE NEVER SAW THE ACFT UNTIL WE WERE IN AN RA; TCAS WAS INSTRUMENTAL IN RPTING AND HELPING PREVENT THIS MIDAIR. PLEASE LOG THIS EVENT AS AN NMAC.

Data retrieved from NASA's ASRS site as of January 2009 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.

An A320 approaching las experienced an RA with TCAS detected VFR traffic that ATC had no transponder for.