A B757 crew had less than standard separation with a VFR PA28 in ZLA class east airspace.

Attributes
ACN	578411
Time
Date	200304
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : ipl.vortac
State Reference	CA
Altitude	msl bound lower : 10000 msl bound upper : 10300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla.artcc
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	climbout : intermediate altitude
Route In Use	arrival star : baret
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zla.artcc
Operator	general aviation : personal
Make Model Name	PA-28 Cherokee/Archer II/Dakota/Pillan/Warrior
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 13535 flight time type : 1116
ASRS Report	578411
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne critical non adherence : far non adherence : published procedure
Independent Detector	aircraft equipment : tcas other flight crewa other flight crewb
Resolutory Action	controller : issued advisory flight crew : took evasive action other
Miss Distance	horizontal : 100 vertical : 500
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

While descending for arrival into san, we experienced a potential altitude conflict with opposite direction VFR traffic while under ZLA control. We were given clearance to cross pillo intersection at 10000 ft. Just past pillo, center advised us of opposite direction traffic at 9500 ft. WX conditions were VFR on top, with tops at 8500 ft. Traffic was piper cherokee opposite direction at 20 mi west. We observed traffic on TCASII initially, indicating -200 ft from our current assigned altitude of 10000 ft. I queried ATC to verify altitude of approaching traffic. ZLA controller informed cherokee his display showed him at 9800 ft. Cherokee responded that he was at 9600 ft. At 5 mi, we deviated to 10300 ft with a subsequent TCASII RA indicating not to descend, and informed center of TCASII climb. We had visual observation of traffic approaching head on 5 mi range. TCASII now indicating traffic at -500 ft while we were at 10300 ft. We passed overhead traffic at 10300 ft with 500 ft altitude difference indicated on TCASII. Without TCASII and deviation on our part, we would have had a near miss and potential conflict.

Original NASA ASRS Text

Title: A B757 CREW HAD LTSS WITH A VFR PA28 IN ZLA CLASS E AIRSPACE.

Narrative: WHILE DSNDING FOR ARR INTO SAN, WE EXPERIENCED A POTENTIAL ALT CONFLICT WITH OPPOSITE DIRECTION VFR TFC WHILE UNDER ZLA CTL. WE WERE GIVEN CLRNC TO CROSS PILLO INTXN AT 10000 FT. JUST PAST PILLO, CTR ADVISED US OF OPPOSITE DIRECTION TFC AT 9500 FT. WX CONDITIONS WERE VFR ON TOP, WITH TOPS AT 8500 FT. TFC WAS PIPER CHEROKEE OPPOSITE DIRECTION AT 20 MI W. WE OBSERVED TFC ON TCASII INITIALLY, INDICATING -200 FT FROM OUR CURRENT ASSIGNED ALT OF 10000 FT. I QUERIED ATC TO VERIFY ALT OF APCHING TFC. ZLA CTLR INFORMED CHEROKEE HIS DISPLAY SHOWED HIM AT 9800 FT. CHEROKEE RESPONDED THAT HE WAS AT 9600 FT. AT 5 MI, WE DEVIATED TO 10300 FT WITH A SUBSEQUENT TCASII RA INDICATING NOT TO DSND, AND INFORMED CTR OF TCASII CLB. WE HAD VISUAL OBSERVATION OF TFC APCHING HEAD ON 5 MI RANGE. TCASII NOW INDICATING TFC AT -500 FT WHILE WE WERE AT 10300 FT. WE PASSED OVERHEAD TFC AT 10300 FT WITH 500 FT ALT DIFFERENCE INDICATED ON TCASII. WITHOUT TCASII AND DEV ON OUR PART, WE WOULD HAVE HAD A NEAR MISS AND POTENTIAL CONFLICT.

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.