A GPWS SOFTWARE PROB CAUSES AN ACR MLG TO REVERSE ITS DSCNT.

Narrative

ON AN APPROX 10 MI DOWNWIND RADAR VECTOR INTO SJC; WE WERE DSNDING FROM 5000 FT TO A CLRNC OF 4000 FT. DSCNT RATE WAS APPROX 1500 FPM WITH 250 KTS AND PWR TO IDLE. THE GPWS WENT OFF SAYING 'TERRAIN' AT LEAST 4 TIMES. WE DID COMPLY WITH GA PWR AND CLB. TERRAIN WARNING STOPPED THROUGH ABOUT 5300 FT OR 5500 FT. LEVEL OFF DUE TO HIGH RATE OF CLB WAS AT 6500 FT. NO CONFLICT OCCURRED. I CALLED THE CTLR ON A LAND LINE. HE INFORMED ME THAT THIS HAPPENS EVERY ONCE IN A WHILE. SEEMS TO ME THAT THIS NEEDS TO BE CORRECTED. AS WE WERE IN THE CLOUDS; THERE IS NO TIME TO ANALYZE THE SIT. FOR ALL I KNOW; THERE WAS TERRAIN! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS FLYING THE JAWWS 1 STAR INTO SJC; SETTING UP FOR A L TURN IN FOR A VISUAL APCH TO RWY 12R. HIS ACR HAS RPTED BACK THAT THERE IS A PROB WITH THE GPWS SOFTWARE AND THE MANUFACTURER IS WORKING ON IT. THE RPTR BELIEVES THAT BAY TRACON LETS ACFT DOWN TO A MARGINAL ALT OVER HIGH TERRAIN IN THE EFFORT TO SEPARATE TFC INTO OAK AND SFO. HIS ACR HAS PUBLISHED SPECIAL PAGES FOR ITS MANUALS DEALING WITH GPWS PROBS FOR RNO AND BUR; BUT NOT SJC. THIS OCCURRED IN MID-AFTERNOON. THE RPTR WAS IMC AT THE TIME OF THE ALERT; BUT SJC WX WAS ABOUT 2000 FT OVCST WITH LIGHT RAIN. THE RPTR WISHES THAT HE HAD INSISTED ON AN ILS APCH RATHER THAN VECTORS FOR A VISUAL APCH. HIS 'ESCAPE MANEUVER' PRODUCED NO TFC CONFLICTS.