Narrative:

We were level at 11000 ft when we received a TA from TCASII. Traffic was at 12 O'clock 10600 ft and climbing. I saw him visually and noticed a definite right to left movement. As he reached 11000 ft we got the RA 'descend' (1 time) followed by a command that I missed, then 'climb, climb now, climb, climb now.' the first officer turned off the autoplt, and followed the RA guidance. At 11600 ft the TCASII gave a 'clear of conflict' and we returned to 11000 ft. Notified approach control of the altitude deviation. Approach said that perhaps they should have mentioned the traffic. He was VFR, but approach apparently knew he was there. Callback conversation with reporter revealed the following information: the controller knew of the light aircraft's presence prior to the flight crew getting the TCASII RA, but for some reason did not tell them about it. The captain said that he watched the TCASII as the aircraft's return showed that he was climbing and saw that it was going to intrude into their area. He said to the first officer that he should get ready for a warning. The first warning was an RA. The reporter said that he has received several TCASII warnings and they have all been accurate. The other aircraft was a high wing single engine aircraft, but the captain did not have further information.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION. AN ACR RECEIVES A TCASII RA AND CLBS OUT OF DANGER THEN RETURNS TO ITS ORIGINAL ALT AND COURSE.

Narrative: WE WERE LEVEL AT 11000 FT WHEN WE RECEIVED A TA FROM TCASII. TFC WAS AT 12 O'CLOCK 10600 FT AND CLBING. I SAW HIM VISUALLY AND NOTICED A DEFINITE R TO L MOVEMENT. AS HE REACHED 11000 FT WE GOT THE RA 'DSND' (1 TIME) FOLLOWED BY A COMMAND THAT I MISSED, THEN 'CLB, CLB NOW, CLB, CLB NOW.' THE FO TURNED OFF THE AUTOPLT, AND FOLLOWED THE RA GUIDANCE. AT 11600 FT THE TCASII GAVE A 'CLR OF CONFLICT' AND WE RETURNED TO 11000 FT. NOTIFIED APCH CTL OF THE ALTDEV. APCH SAID THAT PERHAPS THEY SHOULD HAVE MENTIONED THE TFC. HE WAS VFR, BUT APCH APPARENTLY KNEW HE WAS THERE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CTLR KNEW OF THE LIGHT ACFT'S PRESENCE PRIOR TO THE FLC GETTING THE TCASII RA, BUT FOR SOME REASON DID NOT TELL THEM ABOUT IT. THE CAPT SAID THAT HE WATCHED THE TCASII AS THE ACFT'S RETURN SHOWED THAT HE WAS CLBING AND SAW THAT IT WAS GOING TO INTRUDE INTO THEIR AREA. HE SAID TO THE FO THAT HE SHOULD GET READY FOR A WARNING. THE FIRST WARNING WAS AN RA. THE RPTR SAID THAT HE HAS RECEIVED SEVERAL TCASII WARNINGS AND THEY HAVE ALL BEEN ACCURATE. THE OTHER ACFT WAS A HIGH WING SINGLE ENG ACFT, BUT THE CAPT DID NOT HAVE FURTHER INFO.

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.