TCASII RA dictate descent to avoid traffic.

Attributes
ACN	187074
Time
Date	199108
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : oak
State Reference	CA
Altitude	msl bound lower : 3800 msl bound upper : 4000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : oak
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach descent other landing other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : instrument pilot : atp
Experience	flight time last 90 days : 120 flight time total : 5000 flight time type : 35
ASRS Report	187074
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were being vectored for oak ILS runway 29. We were at 4000 ft, IFR, over the oakland hills, in an unusual summertime rainshower. ATC gave us a 90 degree left turn to avoid VFR traffic, 12 O'clock, at our altitude. As we started the turn the TCASII sounded 'descend'. We initiated descent and advised ATC, which immediately answered with 'your min vectoring altitude' is 3200 ft. At about 3800 ft TCASII sounded 'clear of conflict', we climbed back to 4000. The other aircraft was not sighted at any time. It may have been operating VFR outside the rainshower and outside the san francisco TCA. The TCASII and ATC performed perfectly. Special thanks to the controller who so quickly advised us of our potential terrain problem.

Original NASA ASRS Text

Title: TCASII RA DICTATE DSCNT TO AVOID TFC.

Narrative: WE WERE BEING VECTORED FOR OAK ILS RWY 29. WE WERE AT 4000 FT, IFR, OVER THE OAKLAND HILLS, IN AN UNUSUAL SUMMERTIME RAINSHOWER. ATC GAVE US A 90 DEG L TURN TO AVOID VFR TFC, 12 O'CLOCK, AT OUR ALT. AS WE STARTED THE TURN THE TCASII SOUNDED 'DSND'. WE INITIATED DSCNT AND ADVISED ATC, WHICH IMMEDIATELY ANSWERED WITH 'YOUR MIN VECTORING ALT' IS 3200 FT. AT ABOUT 3800 FT TCASII SOUNDED 'CLR OF CONFLICT', WE CLBED BACK TO 4000. THE OTHER ACFT WAS NOT SIGHTED AT ANY TIME. IT MAY HAVE BEEN OPERATING VFR OUTSIDE THE RAINSHOWER AND OUTSIDE THE SAN FRANCISCO TCA. THE TCASII AND ATC PERFORMED PERFECTLY. SPECIAL THANKS TO THE CTLR WHO SO QUICKLY ADVISED US OF OUR POTENTIAL TERRAIN PROBLEM.

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.