Narrative:

Air carrier X was being handled by the san approach (ATC) control and was at 6000' MSL on the downwind leg and being vectored for the approach by ATC. Abeam the airport, a clearance was given to descend to 5000' MSL, followed shortly thereafter by an additional clearance to continue the descent to 4000' MSL. The aircraft at this time while descending is on base leg for the runway and flying in the clouds with no forward visibility. The flight is then given a heading to intercept the localizer outside the final approach fix, and to continue the descent to 2100'. The crew questioned this latest clearance and was told by the controller that the altitude, heading and approach clearance was correct. One reason the crew was so skeptical was the fact that they have made repeated approachs to this runway (runway 27) over the past yr and were aware of the terrain and obstructions in the area. The aircraft was configured with the gear down, flaps 15, and descending (approximately 1000-1500 FPM). While on approach, the ground proximity warning went off and the words 'terrain, terrain' were heard. A quick scan of the flight instruments indicated all was normal, with the exception of the radar altimeter--it was fluctuating and showing a loss of altitude (from 1500-900' AGL). Upon first indication of the ground proximity going off, power was added, descent was discontinued and preparations were being made for a missed approach. During all of this, ATC was again asked to verify the altitude that the flight was cleared to. Again this was verified as 2100' MSL. At this pint in time, the aircraft started a climb. During this entire sequence of events, the crew was extremely concerned that an error was made by the controller because air carrier X was the first aircraft on approach and others (air carrier's) were to follow. Another indication and/or cause for concern was that neither of the crew members had ever received a clearance to go that low on the approach that far from the airport. Approach control gave the flight a new heading to intercept the localizer from the other side (south), track it inbound, and again cleared for the approach. The flight continued inbound, broke out of the clouds, and landed uneventfully. After landing and securing the aircraft, the captain contacted the san tower and explained the reason for the climb and the non-standard type of flying during the approach--ground proximity going off and radar altimeter readings.

Related reports:

Google
 

Original NASA ASRS Text

Title: GPWS ACTIVATED WHILE ON RADAR VECTOR AND DESCENDING FOR APCH.

Narrative: ACR X WAS BEING HANDLED BY THE SAN APCH (ATC) CTL AND WAS AT 6000' MSL ON THE DOWNWIND LEG AND BEING VECTORED FOR THE APCH BY ATC. ABEAM THE ARPT, A CLRNC WAS GIVEN TO DSND TO 5000' MSL, FOLLOWED SHORTLY THEREAFTER BY AN ADDITIONAL CLRNC TO CONTINUE THE DSCNT TO 4000' MSL. THE ACFT AT THIS TIME WHILE DSNDING IS ON BASE LEG FOR THE RWY AND FLYING IN THE CLOUDS WITH NO FORWARD VISIBILITY. THE FLT IS THEN GIVEN A HDG TO INTERCEPT THE LOC OUTSIDE THE FINAL APCH FIX, AND TO CONTINUE THE DSCNT TO 2100'. THE CREW QUESTIONED THIS LATEST CLRNC AND WAS TOLD BY THE CTLR THAT THE ALT, HDG AND APCH CLRNC WAS CORRECT. ONE REASON THE CREW WAS SO SKEPTICAL WAS THE FACT THAT THEY HAVE MADE REPEATED APCHS TO THIS RWY (RWY 27) OVER THE PAST YR AND WERE AWARE OF THE TERRAIN AND OBSTRUCTIONS IN THE AREA. THE ACFT WAS CONFIGURED WITH THE GEAR DOWN, FLAPS 15, AND DSNDING (APPROX 1000-1500 FPM). WHILE ON APCH, THE GND PROX WARNING WENT OFF AND THE WORDS 'TERRAIN, TERRAIN' WERE HEARD. A QUICK SCAN OF THE FLT INSTRUMENTS INDICATED ALL WAS NORMAL, WITH THE EXCEPTION OF THE RADAR ALTIMETER--IT WAS FLUCTUATING AND SHOWING A LOSS OF ALT (FROM 1500-900' AGL). UPON FIRST INDICATION OF THE GND PROX GOING OFF, PWR WAS ADDED, DSCNT WAS DISCONTINUED AND PREPARATIONS WERE BEING MADE FOR A MISSED APCH. DURING ALL OF THIS, ATC WAS AGAIN ASKED TO VERIFY THE ALT THAT THE FLT WAS CLRED TO. AGAIN THIS WAS VERIFIED AS 2100' MSL. AT THIS PINT IN TIME, THE ACFT STARTED A CLB. DURING THIS ENTIRE SEQUENCE OF EVENTS, THE CREW WAS EXTREMELY CONCERNED THAT AN ERROR WAS MADE BY THE CTLR BECAUSE ACR X WAS THE FIRST ACFT ON APCH AND OTHERS (ACR'S) WERE TO FOLLOW. ANOTHER INDICATION AND/OR CAUSE FOR CONCERN WAS THAT NEITHER OF THE CREW MEMBERS HAD EVER RECEIVED A CLRNC TO GO THAT LOW ON THE APCH THAT FAR FROM THE ARPT. APCH CTL GAVE THE FLT A NEW HDG TO INTERCEPT THE LOC FROM THE OTHER SIDE (S), TRACK IT INBND, AND AGAIN CLRED FOR THE APCH. THE FLT CONTINUED INBND, BROKE OUT OF THE CLOUDS, AND LANDED UNEVENTFULLY. AFTER LNDG AND SECURING THE ACFT, THE CAPT CONTACTED THE SAN TWR AND EXPLAINED THE REASON FOR THE CLB AND THE NON-STANDARD TYPE OF FLYING DURING THE APCH--GND PROX GOING OFF AND RADAR ALTIMETER READINGS.

Data retrieved from NASA's ASRS site as of August 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.