Narrative:

2 TCASII alerts (RA climb, and RA monitor descent) on approach to sea. We did initially start a climb off the GS, but I decided to disregard the warning due to boeing field traffic pattern. I thought that was the cause of the alert. We leveled for a few moments and then started a descent again. The second RA went off, and I turned TCASII off. Prior to the 2 RA alerts, we had a TA but that was behind us. My initial belief that the alerts were caused by boeing field traffic, I feel was incorrect. About the time we passed parkk, a commuter light transport passed us up. He was visual for 16L. He was the cause of the alerts, but his clearance was to maintain visual with us, and we were not told of his position, or of him passing us. I think his speed was a good 25-30 KTS faster than us. We were told not to exceed 190 KTS (to parkk) if approach control had advised us of light transport traffic, we could have reasoned the cause of the RA alerts. TCASII is a new system, and some bugs need to be worked out. I feel that turning off TCASII, as I did, is defeating the system, and removing a safety factor, however, in the approach mode, doing a go around for every RA alert is not the answer either. With time and experience. We can learn to use the TCASII to its greatest advantage. In our particular situation though, better communication would have (probably) solved our confusion.

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Original NASA ASRS Text

Title: ACR MLG ALTDEV EXCURSION FROM CLRNC ALT IN RESPONSE TO TCASII RA.

Narrative: 2 TCASII ALERTS (RA CLB, AND RA MONITOR DSCNT) ON APCH TO SEA. WE DID INITIALLY START A CLB OFF THE GS, BUT I DECIDED TO DISREGARD THE WARNING DUE TO BOEING FIELD TFC PATTERN. I THOUGHT THAT WAS THE CAUSE OF THE ALERT. WE LEVELED FOR A FEW MOMENTS AND THEN STARTED A DSCNT AGAIN. THE SECOND RA WENT OFF, AND I TURNED TCASII OFF. PRIOR TO THE 2 RA ALERTS, WE HAD A TA BUT THAT WAS BEHIND US. MY INITIAL BELIEF THAT THE ALERTS WERE CAUSED BY BOEING FIELD TFC, I FEEL WAS INCORRECT. ABOUT THE TIME WE PASSED PARKK, A COMMUTER LTT PASSED US UP. HE WAS VISUAL FOR 16L. HE WAS THE CAUSE OF THE ALERTS, BUT HIS CLRNC WAS TO MAINTAIN VISUAL WITH US, AND WE WERE NOT TOLD OF HIS POS, OR OF HIM PASSING US. I THINK HIS SPD WAS A GOOD 25-30 KTS FASTER THAN US. WE WERE TOLD NOT TO EXCEED 190 KTS (TO PARKK) IF APCH CTL HAD ADVISED US OF LTT TFC, WE COULD HAVE REASONED THE CAUSE OF THE RA ALERTS. TCASII IS A NEW SYS, AND SOME BUGS NEED TO BE WORKED OUT. I FEEL THAT TURNING OFF TCASII, AS I DID, IS DEFEATING THE SYS, AND REMOVING A SAFETY FACTOR, HOWEVER, IN THE APCH MODE, DOING A GAR FOR EVERY RA ALERT IS NOT THE ANSWER EITHER. WITH TIME AND EXPERIENCE. WE CAN LEARN TO USE THE TCASII TO ITS GREATEST ADVANTAGE. IN OUR PARTICULAR SITUATION THOUGH, BETTER COM WOULD HAVE (PROBABLY) SOLVED OUR CONFUSION.

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.