Narrative:

Our flight sjc-sna, was on radar downwind, being vectored for ILS 19R approach. We were at 3000 MSL 210 kcas. Approach called converging traffic (light fixed wing) at our 2 O'clock position 3500 ft MSL. Traffic was VFR with approach control letting him pass through the arsa. TCAS showed a 'proximate target' at the position and altitude called by ATC. As we got closer, TCAS announced 'monitor vertical speed' one time followed by 'descend, descend' repeated twice. We descended to approximately 2500 ft MSL when TCAS announced 'clear of traffic.' we announced our reaction to the RA to coast approach. Coast approach seemed very surprised that an 'RA' occurred when there was 'legal separation.' as long as the TCAS software is programmed to keep a 1000 ft vertical safe distance between altitude encoded aircraft this event will occur over and over between VFR and IFR aircraft in an approach departure situation. ATC needs to understand that just because it's 'legal separation' in their book, doesn't mean TCAS won't react. Question: by our reaction (descending) to this resolution advisory, did we not endanger my aircraft and passengers and maybe some other aircraft below us? TCAS is great, don't get me wrong, but if the FAA is going to mandate all schedule air carriers to have it on their aircraft, ATC has to know how to handle TCAS equipped aircraft. Don't mix VFR and IFR in close proximity!

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Original NASA ASRS Text

Title: FLC OF MLG GIVEN VFR TFC 500 FT ABOVE PASSING IN CLOSE PROX. TCASII GAVE RA AND FLC DSNDED.

Narrative: OUR FLT SJC-SNA, WAS ON RADAR DOWNWIND, BEING VECTORED FOR ILS 19R APCH. WE WERE AT 3000 MSL 210 KCAS. APCH CALLED CONVERGING TFC (LIGHT FIXED WING) AT OUR 2 O'CLOCK POS 3500 FT MSL. TFC WAS VFR WITH APCH CTL LETTING HIM PASS THROUGH THE ARSA. TCAS SHOWED A 'PROXIMATE TARGET' AT THE POS AND ALT CALLED BY ATC. AS WE GOT CLOSER, TCAS ANNOUNCED 'MONITOR VERT SPD' ONE TIME FOLLOWED BY 'DSND, DSND' REPEATED TWICE. WE DSNDED TO APPROX 2500 FT MSL WHEN TCAS ANNOUNCED 'CLR OF TFC.' WE ANNOUNCED OUR REACTION TO THE RA TO COAST APCH. COAST APCH SEEMED VERY SURPRISED THAT AN 'RA' OCCURRED WHEN THERE WAS 'LEGAL SEPARATION.' AS LONG AS THE TCAS SOFTWARE IS PROGRAMMED TO KEEP A 1000 FT VERT SAFE DISTANCE BTWN ALT ENCODED ACFT THIS EVENT WILL OCCUR OVER AND OVER BTWN VFR AND IFR ACFT IN AN APCH DEP SITUATION. ATC NEEDS TO UNDERSTAND THAT JUST BECAUSE IT'S 'LEGAL SEPARATION' IN THEIR BOOK, DOESN'T MEAN TCAS WON'T REACT. QUESTION: BY OUR REACTION (DSNDING) TO THIS RESOLUTION ADVISORY, DID WE NOT ENDANGER MY ACFT AND PAXS AND MAYBE SOME OTHER ACFT BELOW US? TCAS IS GREAT, DON'T GET ME WRONG, BUT IF THE FAA IS GOING TO MANDATE ALL SCHEDULE AIR CARRIERS TO HAVE IT ON THEIR ACFT, ATC HAS TO KNOW HOW TO HANDLE TCAS EQUIPPED ACFT. DON'T MIX VFR AND IFR IN CLOSE PROX!

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.