Narrative:

While level at 10000 ft, ATC advised us of traffic at 12 O'clock 6 mi. I did not see the traffic at this time, but noted that the TCASII showed traffic in that location at our altitude. Moments later TCASII gave an aural TA and a yellow circle visual alert. I then saw the traffic approaching head on at approximately 3 mi. As I was considering the best plan of action, ATC called with a more urgent TA (now 1-2 mi distant) and a clearance to turn left to a specific heading. During the ATC xmissions I told the first officer I had the traffic in sight, the TCASII gave an aural 'descend, descend,' I disengaged the autoplt and started a gentle descent followed by a left turn. TCASII then announced 'monitor vertical speed' as I maneuvered the aircraft so as to remain outside the red boundaries on the attitude indicator. I told the first officer to 'tell him we are deviating for an RA,' referring to ATC. ATC immediately gave us a clearance to 7000 ft. I estimate our altitude at 9800 ft when we received the clearance. The traffic passed off our right at approximately 200-300 ft. At about 300 ft above us and TCASII announced 'clear of conflict!! The aircraft was a mostly white C421 which I was able to spot more easily because the left wingtip landing light was on. Our speed reached 255 KIAS. So I reduced the pitch down to bleed the speed below 250 before continuing the descent to 7000 ft. We later asked for and received a telephone number for bay approach. I talked with an approach control supervisor when we arrived in oakland and was told the 421 had leveled at 9800 ft then started a very shallow climb when the controller first called it as traffic for us. The 421 was squawking 1200, not talking to ATC, and continued a climb very slowly to 11700 ft out a heavily travelled arrival route to the bay area. The supervisor also stated the 421 affected 2 other acrs following us. The supervisor also stated that our descent in response to the TCASII RA resulted in no effect on traffic separation. A later debrief of the flight attendants revealed they were not aware of any unusual maneuvering on our arrival to oakland, and could not remember hearing the TCASII aural warnings blaring through the cockpit door. I feel this is a textbook example of how TCASII and ATC are supposed to function in conflicts like this.

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Original NASA ASRS Text

Title: NMAC BTWN AN ACR MLG AND A C421 ON A HEAVILY TRAVELLED ARR RTE.

Narrative: WHILE LEVEL AT 10000 FT, ATC ADVISED US OF TFC AT 12 O'CLOCK 6 MI. I DID NOT SEE THE TFC AT THIS TIME, BUT NOTED THAT THE TCASII SHOWED TFC IN THAT LOCATION AT OUR ALT. MOMENTS LATER TCASII GAVE AN AURAL TA AND A YELLOW CIRCLE VISUAL ALERT. I THEN SAW THE TFC APCHING HEAD ON AT APPROX 3 MI. AS I WAS CONSIDERING THE BEST PLAN OF ACTION, ATC CALLED WITH A MORE URGENT TA (NOW 1-2 MI DISTANT) AND A CLRNC TO TURN L TO A SPECIFIC HDG. DURING THE ATC XMISSIONS I TOLD THE FO I HAD THE TFC IN SIGHT, THE TCASII GAVE AN AURAL 'DSND, DSND,' I DISENGAGED THE AUTOPLT AND STARTED A GENTLE DSCNT FOLLOWED BY A L TURN. TCASII THEN ANNOUNCED 'MONITOR VERT SPD' AS I MANEUVERED THE ACFT SO AS TO REMAIN OUTSIDE THE RED BOUNDARIES ON THE ATTITUDE INDICATOR. I TOLD THE FO TO 'TELL HIM WE ARE DEVIATING FOR AN RA,' REFERRING TO ATC. ATC IMMEDIATELY GAVE US A CLRNC TO 7000 FT. I ESTIMATE OUR ALT AT 9800 FT WHEN WE RECEIVED THE CLRNC. THE TFC PASSED OFF OUR R AT APPROX 200-300 FT. AT ABOUT 300 FT ABOVE US AND TCASII ANNOUNCED 'CLR OF CONFLICT!! THE ACFT WAS A MOSTLY WHITE C421 WHICH I WAS ABLE TO SPOT MORE EASILY BECAUSE THE L WINGTIP LNDG LIGHT WAS ON. OUR SPD REACHED 255 KIAS. SO I REDUCED THE PITCH DOWN TO BLEED THE SPD BELOW 250 BEFORE CONTINUING THE DSCNT TO 7000 FT. WE LATER ASKED FOR AND RECEIVED A TELEPHONE NUMBER FOR BAY APCH. I TALKED WITH AN APCH CTL SUPVR WHEN WE ARRIVED IN OAKLAND AND WAS TOLD THE 421 HAD LEVELED AT 9800 FT THEN STARTED A VERY SHALLOW CLB WHEN THE CTLR FIRST CALLED IT AS TFC FOR US. THE 421 WAS SQUAWKING 1200, NOT TALKING TO ATC, AND CONTINUED A CLB VERY SLOWLY TO 11700 FT OUT A HEAVILY TRAVELLED ARR RTE TO THE BAY AREA. THE SUPVR ALSO STATED THE 421 AFFECTED 2 OTHER ACRS FOLLOWING US. THE SUPVR ALSO STATED THAT OUR DSCNT IN RESPONSE TO THE TCASII RA RESULTED IN NO EFFECT ON TFC SEPARATION. A LATER DEBRIEF OF THE FLT ATTENDANTS REVEALED THEY WERE NOT AWARE OF ANY UNUSUAL MANEUVERING ON OUR ARR TO OAKLAND, AND COULD NOT REMEMBER HEARING THE TCASII AURAL WARNINGS BLARING THROUGH THE COCKPIT DOOR. I FEEL THIS IS A TEXTBOOK EXAMPLE OF HOW TCASII AND ATC ARE SUPPOSED TO FUNCTION IN CONFLICTS LIKE THIS.

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.