Narrative:

After receiving clearance to descend from 12000 to 10000 on the chins 2 arrival into sea, the ZSE controller advised us of traffic at 10000. Shortly thereafter, our TCASII gave us a TA followed a few seconds later by a RA to climb at a rate of 1500 FPM or greater. We initiated a climb from approximately 11200 and notified ATC that we were climbing in response to a TCASII resolution. The controller responded 'that's the traffic I already told you about. ' He also wanted to know how high we intended to climb. A verbal exchange followed in which we tried to make it clear that we were in IMC, and regardless of our flight conditions we are obligated to comply with an RA. He responded 'well, it's a good thing there isn't anybody above you. While this exchange was occurring, TCASII gave us a 'clear of conflict' and we began a descent back to 11000. Due to our concentration on the conversation with the controller, we descended through 11000 to 10850 and immediately corrected back to 11000. 2 factors are important regarding this situation. First, although separation never really even approached 1000 ft vertically and/or horizontally (based on what the controller told us), TCASII didn't 'know' we were going to level 1000 ft above the traffic. It computed the projected loss of separation based on our approximately 500 FPM rate of descent at the time. The point is this: in my opinion, based on this and 1 other TCASII RA I've had, TCASII actually causes far more problems from a human factors standpoint than it prevents from a safety (loss of separation) standpoint. Any RA will attract the attention of every person on the flight deck, and everyone's attention is focused on the RA to the exclusion of just about all else. TCASII is, at a in, much too sensitive. If we must have TCASII, it should be only the 'last ditch' effort in preventing a collision. The second factor important in this situation within the realm of human factors is that controllers must refrain from engaging the crew in a verbal exchange during the response to a TCASII RA. We're already diverting our attention away from flying the airplane to concentrate on the RA. The last thing we need is the controller further diverting our attention. Controllers should simply acknowledge the call and deal only with aircraft separation problems that may arise as a result of the crew flying the RA. The ctrl's concern is understandable. When a crew advises a controller they're deviating from their clearance to comply with a RA, it implies to the controller that he/she made a mistake and jeopardized aircraft separation. A somewhat defensive reaction is only natural. After being personally undecided about the TCASII system for the last 18 mos or so, I am now of the firm opinion that it actually causes (or at least certainly contributes) far more problems then it will ever prevent.

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Original NASA ASRS Text

Title: FLC OF LGT ON DSCNT INTO SEA GETS TCASII RA IN RESPONSE TO TFC CLBING FROM BELOW. FLC RESPONDS BY CLBING BECAUSE THEY WERE OBLIGATED TO DO SO SINCE THEY WERE IN IMC.

Narrative: AFTER RECEIVING CLRNC TO DSND FROM 12000 TO 10000 ON THE CHINS 2 ARR INTO SEA, THE ZSE CTLR ADVISED US OF TFC AT 10000. SHORTLY THEREAFTER, OUR TCASII GAVE US A TA FOLLOWED A FEW SECONDS LATER BY A RA TO CLB AT A RATE OF 1500 FPM OR GREATER. WE INITIATED A CLB FROM APPROX 11200 AND NOTIFIED ATC THAT WE WERE CLBING IN RESPONSE TO A TCASII RESOLUTION. THE CTLR RESPONDED 'THAT'S THE TFC I ALREADY TOLD YOU ABOUT. ' HE ALSO WANTED TO KNOW HOW HIGH WE INTENDED TO CLB. A VERBAL EXCHANGE FOLLOWED IN WHICH WE TRIED TO MAKE IT CLR THAT WE WERE IN IMC, AND REGARDLESS OF OUR FLT CONDITIONS WE ARE OBLIGATED TO COMPLY WITH AN RA. HE RESPONDED 'WELL, IT'S A GOOD THING THERE ISN'T ANYBODY ABOVE YOU. WHILE THIS EXCHANGE WAS OCCURRING, TCASII GAVE US A 'CLR OF CONFLICT' AND WE BEGAN A DSCNT BACK TO 11000. DUE TO OUR CONCENTRATION ON THE CONVERSATION WITH THE CTLR, WE DSNDED THROUGH 11000 TO 10850 AND IMMEDIATELY CORRECTED BACK TO 11000. 2 FACTORS ARE IMPORTANT REGARDING THIS SITUATION. FIRST, ALTHOUGH SEPARATION NEVER REALLY EVEN APCHED 1000 FT VERTICALLY AND/OR HORIZLY (BASED ON WHAT THE CTLR TOLD US), TCASII DIDN'T 'KNOW' WE WERE GOING TO LEVEL 1000 FT ABOVE THE TFC. IT COMPUTED THE PROJECTED LOSS OF SEPARATION BASED ON OUR APPROX 500 FPM RATE OF DSCNT AT THE TIME. THE POINT IS THIS: IN MY OPINION, BASED ON THIS AND 1 OTHER TCASII RA I'VE HAD, TCASII ACTUALLY CAUSES FAR MORE PROBLEMS FROM A HUMAN FACTORS STANDPOINT THAN IT PREVENTS FROM A SAFETY (LOSS OF SEPARATION) STANDPOINT. ANY RA WILL ATTRACT THE ATTN OF EVERY PERSON ON THE FLT DECK, AND EVERYONE'S ATTN IS FOCUSED ON THE RA TO THE EXCLUSION OF JUST ABOUT ALL ELSE. TCASII IS, AT A IN, MUCH TOO SENSITIVE. IF WE MUST HAVE TCASII, IT SHOULD BE ONLY THE 'LAST DITCH' EFFORT IN PREVENTING A COLLISION. THE SECOND FACTOR IMPORTANT IN THIS SITUATION WITHIN THE REALM OF HUMAN FACTORS IS THAT CTLRS MUST REFRAIN FROM ENGAGING THE CREW IN A VERBAL EXCHANGE DURING THE RESPONSE TO A TCASII RA. WE'RE ALREADY DIVERTING OUR ATTN AWAY FROM FLYING THE AIRPLANE TO CONCENTRATE ON THE RA. THE LAST THING WE NEED IS THE CTLR FURTHER DIVERTING OUR ATTN. CTLRS SHOULD SIMPLY ACKNOWLEDGE THE CALL AND DEAL ONLY WITH ACFT SEPARATION PROBLEMS THAT MAY ARISE AS A RESULT OF THE CREW FLYING THE RA. THE CTRL'S CONCERN IS UNDERSTANDABLE. WHEN A CREW ADVISES A CTLR THEY'RE DEVIATING FROM THEIR CLRNC TO COMPLY WITH A RA, IT IMPLIES TO THE CTLR THAT HE/SHE MADE A MISTAKE AND JEOPARDIZED ACFT SEPARATION. A SOMEWHAT DEFENSIVE REACTION IS ONLY NATURAL. AFTER BEING PERSONALLY UNDECIDED ABOUT THE TCASII SYS FOR THE LAST 18 MOS OR SO, I AM NOW OF THE FIRM OPINION THAT IT ACTUALLY CAUSES (OR AT LEAST CERTAINLY CONTRIBUTES) FAR MORE PROBLEMS THEN IT WILL EVER PREVENT.

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.