Flight crew of B737 received TCASII RA due to VFR traffic during descent to oak.

Attributes
ACN	578276
Time
Date	200304
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : oak.airport
State Reference	CA
Altitude	msl single value : 5200
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : nct.tracon
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : nct.tracon
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 140 flight time total : 6500 flight time type : 3000
ASRS Report	578276
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	conflict : nmac
Independent Detector	aircraft equipment : tcas
Resolutory Action	flight crew : took evasive action flight crew : returned to assigned altitude
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 200
Supplementary
Problem Areas	Weather ATC Human Performance Airspace Structure Environmental Factor
Primary Problem	Airspace Structure

Narrative:

We were on a vector to the oak airport and were IMC and told to descend to 5000 ft. Norcal approach informed us of VFR traffic at 4500 ft at 12 O'clock position. We acknowledged, and we heard the VFR traffic acknowledge us. Passing 5200 ft, we received a TCASII RA to descend. I was a bit confused, because of our altitude and what norcal had called the VFR traffic altitude at. The first officer punched off the autoplt, and began to descend and immediately received a TCASII RA to climb, climb now! He started to climb, and we topped out at about 5500 ft. We were IFR, so I checked the TCASII and noted at one time, the VFR traffic was 200 ft below us. I don't believe our aircraft went below 5000 ft during the TCASII maneuver, and the VFR traffic passed within 200 ft of altitude from us. We continued and landed at oak. I called norcal approach, explained the situation, and he suggested I submit a NASA report. This is submitted, not because I feel our aircraft did anything incorrectly, but because it will generate a NASA report.

Original NASA ASRS Text

Title: FLC OF B737 RECEIVED TCASII RA DUE TO VFR TFC DURING DSCNT TO OAK.

Narrative: WE WERE ON A VECTOR TO THE OAK ARPT AND WERE IMC AND TOLD TO DSND TO 5000 FT. NORCAL APCH INFORMED US OF VFR TFC AT 4500 FT AT 12 O'CLOCK POS. WE ACKNOWLEDGED, AND WE HEARD THE VFR TFC ACKNOWLEDGE US. PASSING 5200 FT, WE RECEIVED A TCASII RA TO DSND. I WAS A BIT CONFUSED, BECAUSE OF OUR ALT AND WHAT NORCAL HAD CALLED THE VFR TFC ALT AT. THE FO PUNCHED OFF THE AUTOPLT, AND BEGAN TO DSND AND IMMEDIATELY RECEIVED A TCASII RA TO CLB, CLB NOW! HE STARTED TO CLB, AND WE TOPPED OUT AT ABOUT 5500 FT. WE WERE IFR, SO I CHKED THE TCASII AND NOTED AT ONE TIME, THE VFR TFC WAS 200 FT BELOW US. I DON'T BELIEVE OUR ACFT WENT BELOW 5000 FT DURING THE TCASII MANEUVER, AND THE VFR TFC PASSED WITHIN 200 FT OF ALT FROM US. WE CONTINUED AND LANDED AT OAK. I CALLED NORCAL APCH, EXPLAINED THE SIT, AND HE SUGGESTED I SUBMIT A NASA RPT. THIS IS SUBMITTED, NOT BECAUSE I FEEL OUR ACFT DID ANYTHING INCORRECTLY, BUT BECAUSE IT WILL GENERATE A NASA RPT.

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.