Narrative:

The first officer was turning onto a visual approach for runway 28L at sfo when TCASII alerted us to a target at 12 O'clock, 50 ft above our altitude. We received an RA and descended and turned to avoid conflict. I questioned approach about other traffic in the area, and their radar nor our visual checks showed any traffic. Runway 28R was closed at the time and we were issued a visual approach to runway 28L -- not the approach. The airplane slightly crossed the final approach course during this event and 2 other similar events inbound. Again we questioned the tower and no traffic was observed on their radar. A strong 20 KT wind out of the south also contributed to the slight overshoot, but the main cause was our constant search and response to RA's which I now believe to have been false targets. Upon landing we notified maintenance and I called bay approach to southeast if we had caused any problems. The supervisor advised me that there was no problem. This is a very difficult decision as had there been runway 28R traffic and an RA which our company policy calls for immediate action a more serious situation could have occurred in the future if we had caused any problems. The supervisor advised me that there was no problem. This is a very difficult decision as had their been runway 28R traffic and an RA which our company policy calls for immediate action a more serious situation could have occurred in the future if I had time to analyze I would definitely turn left if the target was avoidable in that direction. This situation is very unusual as I have only had false TCASII RA's on one other occasion. Unfortunately, TCASII doesn't always work!

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Original NASA ASRS Text

Title: FALSE RA'S CAUSING PLT TO DEVIATE FROM APCH COURSE.

Narrative: THE FO WAS TURNING ONTO A VISUAL APCH FOR RWY 28L AT SFO WHEN TCASII ALERTED US TO A TARGET AT 12 O'CLOCK, 50 FT ABOVE OUR ALT. WE RECEIVED AN RA AND DSNDED AND TURNED TO AVOID CONFLICT. I QUESTIONED APCH ABOUT OTHER TFC IN THE AREA, AND THEIR RADAR NOR OUR VISUAL CHKS SHOWED ANY TFC. RWY 28R WAS CLOSED AT THE TIME AND WE WERE ISSUED A VISUAL APCH TO RWY 28L -- NOT THE APCH. THE AIRPLANE SLIGHTLY CROSSED THE FINAL APCH COURSE DURING THIS EVENT AND 2 OTHER SIMILAR EVENTS INBOUND. AGAIN WE QUESTIONED THE TWR AND NO TFC WAS OBSERVED ON THEIR RADAR. A STRONG 20 KT WIND OUT OF THE S ALSO CONTRIBUTED TO THE SLIGHT OVERSHOOT, BUT THE MAIN CAUSE WAS OUR CONSTANT SEARCH AND RESPONSE TO RA'S WHICH I NOW BELIEVE TO HAVE BEEN FALSE TARGETS. UPON LNDG WE NOTIFIED MAINT AND I CALLED BAY APCH TO SE IF WE HAD CAUSED ANY PROBS. THE SUPVR ADVISED ME THAT THERE WAS NO PROB. THIS IS A VERY DIFFICULT DECISION AS HAD THERE BEEN RWY 28R TFC AND AN RA WHICH OUR COMPANY POLICY CALLS FOR IMMEDIATE ACTION A MORE SERIOUS SIT COULD HAVE OCCURRED IN THE FUTURE IF WE HAD CAUSED ANY PROBS. THE SUPVR ADVISED ME THAT THERE WAS NO PROB. THIS IS A VERY DIFFICULT DECISION AS HAD THEIR BEEN RWY 28R TFC AND AN RA WHICH OUR COMPANY POLICY CALLS FOR IMMEDIATE ACTION A MORE SERIOUS SIT COULD HAVE OCCURRED IN THE FUTURE IF I HAD TIME TO ANALYZE I WOULD DEFINITELY TURN L IF THE TARGET WAS AVOIDABLE IN THAT DIRECTION. THIS SIT IS VERY UNUSUAL AS I HAVE ONLY HAD FALSE TCASII RA'S ON ONE OTHER OCCASION. UNFORTUNATELY, TCASII DOESN'T ALWAYS WORK!

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.