FLC OF WDB HAD TCASII RA DSND AND STARTED DSCNT ADVISING APCH CTLR WHO INSTRUCTED TO MAINTAIN ALT ACCOUNT TFC 1000 FT BELOW OPPOSITE DIRECTION. INTRUDER WAS HIGH DSCNT MLG TO 1000 FT ABOVE THE WDB FLT.

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OAKLAND CENTER HAD JUST GIVEN US CLRNC TO DSND TO 11000 FT SLOW TO 250 KTS. AFTER SLOWING WE DSNDED AND LEVELED AT 11000. TCASII ALERT TFC TFC FOLLOWED BY DSND DSND. A QUICK GLANCE AT THE CRT SHOWED AN ACFT SUPERIMPOSING ITSELF ON US. A FLICK OF THE AUTOPLT AND A PUSH ON THE YOKE STARTED OUR DSCNT. THE COPLT CALLED APCH AND TOLD THEM WE WERE DSNDING ON A TCASII RA. APCH SAID MAINTAIN 11000. ACFT 12 O'CLOCK 3 MI OPPOSITE DIRECTION. APCH ALSO TOLD US OF AN ACFT PASSING 1000 FT ABOVE US ON THE SAME ARR GOING TO SJC; AN MLG. THE ACFT SPOTTED AT THIS TIME PASSING US 1000 FT ABOVE AT ABOUT 300 PLUS KTS AN EASE BACK TO 11000 FT WAS SIMULTANEOUSLY MADE. WHILE ALL OF THIS WAS TRANSPIRING TOTAL LOSS OF ALT 60-100 FT ESTIMATED. IT APPEARS THAT THE TCASII DID ITS JOB BUT NOT IN THE MANNER IT IS PROGRAMMED TO DO. THE MLG WAS FAST DSNDING FROM ALT TO 12000 IN ACCORDANCE WITH HIS CLRNC. HIS SPD WAS NOT SLOWED AS OURS WAS IN VIEW OF THE FACT THAT HE WAS GOING TO AN ARPT 30 MI FURTHER AWAY. HIS RATE OF DSCNT AND SPD TRIGGERED OUR TCASII TO INTERPRET A THREAT TO US. COMPANY WRITTEN POLICY IS TO OBEY THE TCASII THIS COULD HAVE CAUSED A MID AIR IF WX HAD BEEN IFR. THE ACFT AT 12 O'CLOCK 3 MI WOULD HAVE BEEN THE UNSUSPECTING RECIPIENT OF A WIND SCREEN FULL OF WDB. TCASII IS A STEP IN THE RIGHT DIRECTION BUT NOT RELIABLE ENOUGH TO BE BLINDLY OBEYED. SITUATIONAL AWARENESS IS A MUST. THE MARK 8 MODE 1 EYEBALL/BRAIN IS STILL THE BEST MID AIR PREVENTION.