Apparent malfunction of GPWS and resulting evasive action.

Attributes
ACN	268212
Time
Date	199404
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : sjc
State Reference	CA
Altitude	msl bound lower : 4500 msl bound upper : 5500
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : oak tower : bwi
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 170 flight time total : 10000 flight time type : 2700
ASRS Report	268212
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

While on vectors to land sjc runway 12 at 4500 ft MSL, heading 300 degrees radio altitude began winding down. At approximately 1250 ft on radio altitude GPWS sounded `terrain, terrain.' I disconnected autoplt and automatic throttle and pulled up sharply. Peak altitude approximately 5500 ft MSL. Returned to 4500 ft MSL, assigned, and informed bay approach. Bay approach said minimum vector altitude was 4500 ft MSL. Altimeter settings were checked correct. End of event.

Original NASA ASRS Text

Title: APPARENT MALFUNCTION OF GPWS AND RESULTING EVASIVE ACTION.

Narrative: WHILE ON VECTORS TO LAND SJC RWY 12 AT 4500 FT MSL, HDG 300 DEGS RADIO ALT BEGAN WINDING DOWN. AT APPROX 1250 FT ON RADIO ALT GPWS SOUNDED `TERRAIN, TERRAIN.' I DISCONNECTED AUTOPLT AND AUTO THROTTLE AND PULLED UP SHARPLY. PEAK ALT APPROX 5500 FT MSL. RETURNED TO 4500 FT MSL, ASSIGNED, AND INFORMED BAY APCH. BAY APCH SAID MINIMUM VECTOR ALT WAS 4500 FT MSL. ALTIMETER SETTINGS WERE CHKED CORRECT. END OF EVENT.

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.