Narrative:

While being vectored for an approach to oak airport, we were cleared to maintain 11000 ft MSL. Level at 11000 ft MSL we got a TA on our TCASII. As we looked for the traffic, we got an RA to climb. Traffic was at our 1-2 O'clock position showing 200 ft below and climbing. We looked, attempted to verify with oak approach, and followed the RA, climbing to 11500 MSL. By this time oak approach had been notified of altitude excursion, and they indicated no traffic had been observed. We wondered why the aircraft showed a response on our TCASII, but not on approach control radar, but got no answer. We observed single engine small aircraft Y pass below our aircraft with the TCASII, indicating a 200 ft separation. After complying with RA, we returned to 11000 MSL and further reported situation to oak ATC. Since a previous experience, similar to this one, occurred a month previously, I wanted to know how the other crew members felt. They (first officer and so) indicated a disbelief of oak's radar controller failure of picking up the small aircraft Y transponder reply, since our TCASII received sufficient data to give us the appropriate warning. In addition, we all agreed that the TCASII had saved our aircraft and our lives from a midair collision (no exaggeration!). We think the 2 color trim small aircraft was flying VFR unaware of his close proximity to the inbound arrival gate used by oak (and sfo) and we had to wonder if this small aircraft pilot was as shaken by the near miss as we were. If the controled airspace system is going to be used and relied on, then ATC must have a better grip on 'their' airspace -- otherwise, do away with the controled airspace and return to a completely 'see and avoid -- everyone takes their chances' system.

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Original NASA ASRS Text

Title: NMAC ALTDEV ALT EXCURSION.

Narrative: WHILE BEING VECTORED FOR AN APCH TO OAK ARPT, WE WERE CLRED TO MAINTAIN 11000 FT MSL. LEVEL AT 11000 FT MSL WE GOT A TA ON OUR TCASII. AS WE LOOKED FOR THE TFC, WE GOT AN RA TO CLB. TFC WAS AT OUR 1-2 O'CLOCK POS SHOWING 200 FT BELOW AND CLBING. WE LOOKED, ATTEMPTED TO VERIFY WITH OAK APCH, AND FOLLOWED THE RA, CLBING TO 11500 MSL. BY THIS TIME OAK APCH HAD BEEN NOTIFIED OF ALT EXCURSION, AND THEY INDICATED NO TFC HAD BEEN OBSERVED. WE WONDERED WHY THE ACFT SHOWED A RESPONSE ON OUR TCASII, BUT NOT ON APCH CTL RADAR, BUT GOT NO ANSWER. WE OBSERVED SINGLE ENG SMA Y PASS BELOW OUR ACFT WITH THE TCASII, INDICATING A 200 FT SEPARATION. AFTER COMPLYING WITH RA, WE RETURNED TO 11000 MSL AND FURTHER RPTED SITUATION TO OAK ATC. SINCE A PREVIOUS EXPERIENCE, SIMILAR TO THIS ONE, OCCURRED A MONTH PREVIOUSLY, I WANTED TO KNOW HOW THE OTHER CREW MEMBERS FELT. THEY (FO AND SO) INDICATED A DISBELIEF OF OAK'S RADAR CTLR FAILURE OF PICKING UP THE SMA Y TRANSPONDER REPLY, SINCE OUR TCASII RECEIVED SUFFICIENT DATA TO GIVE US THE APPROPRIATE WARNING. IN ADDITION, WE ALL AGREED THAT THE TCASII HAD SAVED OUR ACFT AND OUR LIVES FROM A MIDAIR COLLISION (NO EXAGGERATION!). WE THINK THE 2 COLOR TRIM SMA WAS FLYING VFR UNAWARE OF HIS CLOSE PROX TO THE INBOUND ARR GATE USED BY OAK (AND SFO) AND WE HAD TO WONDER IF THIS SMA PLT WAS AS SHAKEN BY THE NEAR MISS AS WE WERE. IF THE CTLED AIRSPACE SYS IS GOING TO BE USED AND RELIED ON, THEN ATC MUST HAVE A BETTER GRIP ON 'THEIR' AIRSPACE -- OTHERWISE, DO AWAY WITH THE CTLED AIRSPACE AND RETURN TO A COMPLETELY 'SEE AND AVOID -- EVERYONE TAKES THEIR CHANCES' SYS.

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.