Air carrier flight crew experienced a seemingly false GPWS warning due to mechanical malfunction.

Attributes
ACN	1337825
Time
Date	201603
Local Time Of Day	1801-2400
Place
Locale Reference	BUR.Airport
State Reference	CA
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Make Model Name	Medium Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	GPWS
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 250 Flight Crew Total 12000 Flight Crew Type 2000
Person 2
Function	First Officer Pilot Not Flying
Experience	Flight Crew Last 90 Days 251 Flight Crew Total 2310 Flight Crew Type 1000
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance

Narrative:

We were being vectored for the ILS 8 to bur. About 20 miles northwest of the field. We were assigned and were descending to 5;000. About 5;300 feet; our GPWS announced 'terrain; terrain; pull up.' I kicked off the autopilot and climbed aggressively in response. By the time the alert was silenced; we were at about 6;500 feet.we notified ATC; who didn't seem too perturbed; and responded by saying 'minimum vectoring altitude in your area is xx feet' (don't remember the number but it was well below us.) we realized with certainty what I had initially suspected - we were never near terrain and were at a safe altitude at all times. In trying to figure out the issue; and determine why our gear horn was also sounding at the same time; I realized that my radar altimeter showed 0 feet. It had obviously malfunctioned and given the false GPWS warning. We were able to continue our approach and land without incident.we deviated from our ATC clearance; and as it turned out it was unnecessary to do so; but when you're in IMC and know that you're in high terrain; when that GPWS tells you to pull up; you don't hesitate; you hit the gas and get out of there. We did what we had to do; what we are trained to do. It was just good that it was only a malfunction and not a real safety hazard; and good that no conflict was created with other aircraft.

Original NASA ASRS Text

Title: Air carrier flight crew experienced a seemingly false GPWS warning due to mechanical malfunction.

Narrative: We were being vectored for the ILS 8 to BUR. About 20 miles northwest of the field. We were assigned and were descending to 5;000. About 5;300 feet; our GPWS announced 'Terrain; Terrain; Pull UP.' I kicked off the autopilot and climbed aggressively in response. By the time the alert was silenced; we were at about 6;500 feet.We notified ATC; who didn't seem too perturbed; and responded by saying 'minimum vectoring altitude in your area is XX feet' (don't remember the number but it was well below us.) We realized with certainty what I had initially suspected - we were never near terrain and were at a safe altitude at all times. In trying to figure out the issue; and determine why our gear horn was also sounding at the same time; I realized that my radar altimeter showed 0 feet. It had obviously malfunctioned and given the false GPWS warning. We were able to continue our approach and land without incident.We deviated from our ATC clearance; and as it turned out it was unnecessary to do so; but when you're in IMC and know that you're in high terrain; when that GPWS tells you to pull up; you don't hesitate; you hit the gas and get out of there. We did what we had to do; what we are trained to do. It was just good that it was only a malfunction and not a real safety hazard; and good that no conflict was created with other aircraft.

Data retrieved from NASA's ASRS site 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.