Narrative:

We were cleared for a visual approach to runway 24L to follow an air carrier Y B737 to the airport. The air carrier Y B737 was flying a visual or an ILS approach to runway 24R. At the time of our clearance we were north of the air carrier Y B737 about 4 mi, we had just leveled off at 2500 ft MSL. The air carrier Y aircraft was descending from about 6000 ft MSL on more or less a straight-in position on the runway 24R localizer. That meant that we would cross behind him to align ourself with the parallel runway 24L south of his current flight path. We crossed about 2 mi behind and well below the air carrier Y and established ourselves on the runway 24L localizer. At this point our vertical approach path was flat, we were approaching the GS intercept, while the air carrier Y aircraft was descending and apparently approaching the runway 24R GS from above. Because of the approach speed difference, I estimate the air carrier Y B737 was about 45 KTS slower than we were, we were overtaking him. We slowed our aircraft and held a position about 1/4 mi behind him. Both aircraft were established on their respective localizer's. We received a RA because of and directly identifiable to the air carrier Y B737, however, we had him in sight. He was descending into our vertical plane, albeit horizontally separated by the distance of the two different localizer's. We noticed at one point the air carrier Y B737 appeared to be climbing and looked as though he was going to or had broken off the approach. It was our guess that he was receiving RA's from us and not being able to see us was appropriately concerned as to what was going on. The air carrier Y B737 then reestablished his GS to runway 24R and increased his speed. By this time both aircraft were below 1000 ft and no additional RA's were received. I write not to be critical of anyone. Everyone was doing what they should have been doing. The controller was doing a great job of moving aircraft. We were making our visual approach and air carrier Y was doing a fine job. Both aircraft were aligned with their runway and from our perspective no problems were encountered. I'm not too sure that the air carrier Y crew felt the same way. I was thinking of how they must have felt hearing the RA's, remembering the air carrier Z DC9, the previous accident at lax and knowing that lax is a very busy place. Had the radios not have been so congested we would have told air carrier Y that we had them in sight. But remember, this is lax and frequently it's difficult to say what's required, let alone insert cross talk that's outside of the normal flow. There was just no opening to squeeze in what would have helped, 'we have you in sight' as we fell in line behind him. The controller had told him that we had him in sight, but that is of little comfort to any pilot. I don't know what an answer might be to this problem or even if there is one, but if there is anything I can do to help please feel free to call. I'll even volunteer my time to help, after all, the next time it might be me in the overtaken aircraft. Callback conversation with reporter revealed the following information: the reporter said 'this is a ticklish situation.' WX being predominantly VMC most of the thousands of daily airline approachs are visuals. If a pilot ignores the RA on the basis it is being activated by the airplane they know exists, but is outside their field of vision, then someday somehow there is going to be a mix up. The airline and public and everyone else is going to criticize the pilot who was provided the tool at great expense to the industry and did not follow its warning. The reporter stated he was the recipient of the warning recently at stl. To have followed the RA commands would have meant abandoning the approach. The flaps 40 degree limit is 150 KTS on the B737. The flaps will move to 30 degrees going above 150 KTS. Companies do not like pilots to bump the flap limit speeds due to the strain and wear and tear on the flap system. At the same time other aircraft are not faced with such low speed constraints. The suggestion was that controllers be given guidance to assign speeds and vectors that avoid RA activation. The reporter stated the mandated separation is such in IMC approachs that RA activation does not normally occur and/or is not a problem. Visuals are when the problem occurs.

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Original NASA ASRS Text

Title: THE RPTR UNWITTINGLY SET OFF HIS OWN AND PERHAPS ANOTHER ACFT TCASII RA.

Narrative: WE WERE CLRED FOR A VISUAL APCH TO RWY 24L TO FOLLOW AN ACR Y B737 TO THE ARPT. THE ACR Y B737 WAS FLYING A VISUAL OR AN ILS APCH TO RWY 24R. AT THE TIME OF OUR CLRNC WE WERE N OF THE ACR Y B737 ABOUT 4 MI, WE HAD JUST LEVELED OFF AT 2500 FT MSL. THE ACR Y ACFT WAS DSNDING FROM ABOUT 6000 FT MSL ON MORE OR LESS A STRAIGHT-IN POS ON THE RWY 24R LOC. THAT MEANT THAT WE WOULD CROSS BEHIND HIM TO ALIGN OURSELF WITH THE PARALLEL RWY 24L S OF HIS CURRENT FLT PATH. WE CROSSED ABOUT 2 MI BEHIND AND WELL BELOW THE ACR Y AND ESTABLISHED OURSELVES ON THE RWY 24L LOC. AT THIS POINT OUR VERT APCH PATH WAS FLAT, WE WERE APCHING THE GS INTERCEPT, WHILE THE ACR Y ACFT WAS DSNDING AND APPARENTLY APCHING THE RWY 24R GS FROM ABOVE. BECAUSE OF THE APCH SPD DIFFERENCE, I ESTIMATE THE ACR Y B737 WAS ABOUT 45 KTS SLOWER THAN WE WERE, WE WERE OVERTAKING HIM. WE SLOWED OUR ACFT AND HELD A POS ABOUT 1/4 MI BEHIND HIM. BOTH ACFT WERE ESTABLISHED ON THEIR RESPECTIVE LOC'S. WE RECEIVED A RA BECAUSE OF AND DIRECTLY IDENTIFIABLE TO THE ACR Y B737, HOWEVER, WE HAD HIM IN SIGHT. HE WAS DSNDING INTO OUR VERT PLANE, ALBEIT HORIZLY SEPARATED BY THE DISTANCE OF THE TWO DIFFERENT LOC'S. WE NOTICED AT ONE POINT THE ACR Y B737 APPEARED TO BE CLBING AND LOOKED AS THOUGH HE WAS GOING TO OR HAD BROKEN OFF THE APCH. IT WAS OUR GUESS THAT HE WAS RECEIVING RA'S FROM US AND NOT BEING ABLE TO SEE US WAS APPROPRIATELY CONCERNED AS TO WHAT WAS GOING ON. THE ACR Y B737 THEN REESTABLISHED HIS GS TO RWY 24R AND INCREASED HIS SPD. BY THIS TIME BOTH ACFT WERE BELOW 1000 FT AND NO ADDITIONAL RA'S WERE RECEIVED. I WRITE NOT TO BE CRITICAL OF ANYONE. EVERYONE WAS DOING WHAT THEY SHOULD HAVE BEEN DOING. THE CTLR WAS DOING A GREAT JOB OF MOVING ACFT. WE WERE MAKING OUR VISUAL APCH AND ACR Y WAS DOING A FINE JOB. BOTH ACFT WERE ALIGNED WITH THEIR RWY AND FROM OUR PERSPECTIVE NO PROBS WERE ENCOUNTERED. I'M NOT TOO SURE THAT THE ACR Y CREW FELT THE SAME WAY. I WAS THINKING OF HOW THEY MUST HAVE FELT HEARING THE RA'S, REMEMBERING THE ACR Z DC9, THE PREVIOUS ACCIDENT AT LAX AND KNOWING THAT LAX IS A VERY BUSY PLACE. HAD THE RADIOS NOT HAVE BEEN SO CONGESTED WE WOULD HAVE TOLD ACR Y THAT WE HAD THEM IN SIGHT. BUT REMEMBER, THIS IS LAX AND FREQUENTLY IT'S DIFFICULT TO SAY WHAT'S REQUIRED, LET ALONE INSERT CROSS TALK THAT'S OUTSIDE OF THE NORMAL FLOW. THERE WAS JUST NO OPENING TO SQUEEZE IN WHAT WOULD HAVE HELPED, 'WE HAVE YOU IN SIGHT' AS WE FELL IN LINE BEHIND HIM. THE CTLR HAD TOLD HIM THAT WE HAD HIM IN SIGHT, BUT THAT IS OF LITTLE COMFORT TO ANY PLT. I DON'T KNOW WHAT AN ANSWER MIGHT BE TO THIS PROB OR EVEN IF THERE IS ONE, BUT IF THERE IS ANYTHING I CAN DO TO HELP PLEASE FEEL FREE TO CALL. I'LL EVEN VOLUNTEER MY TIME TO HELP, AFTER ALL, THE NEXT TIME IT MIGHT BE ME IN THE OVERTAKEN ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID 'THIS IS A TICKLISH SIT.' WX BEING PREDOMINANTLY VMC MOST OF THE THOUSANDS OF DAILY AIRLINE APCHS ARE VISUALS. IF A PLT IGNORES THE RA ON THE BASIS IT IS BEING ACTIVATED BY THE AIRPLANE THEY KNOW EXISTS, BUT IS OUTSIDE THEIR FIELD OF VISION, THEN SOMEDAY SOMEHOW THERE IS GOING TO BE A MIX UP. THE AIRLINE AND PUBLIC AND EVERYONE ELSE IS GOING TO CRITICIZE THE PLT WHO WAS PROVIDED THE TOOL AT GREAT EXPENSE TO THE INDUSTRY AND DID NOT FOLLOW ITS WARNING. THE RPTR STATED HE WAS THE RECIPIENT OF THE WARNING RECENTLY AT STL. TO HAVE FOLLOWED THE RA COMMANDS WOULD HAVE MEANT ABANDONING THE APCH. THE FLAPS 40 DEG LIMIT IS 150 KTS ON THE B737. THE FLAPS WILL MOVE TO 30 DEGS GOING ABOVE 150 KTS. COMPANIES DO NOT LIKE PLTS TO BUMP THE FLAP LIMIT SPDS DUE TO THE STRAIN AND WEAR AND TEAR ON THE FLAP SYS. AT THE SAME TIME OTHER ACFT ARE NOT FACED WITH SUCH LOW SPD CONSTRAINTS. THE SUGGESTION WAS THAT CTLRS BE GIVEN GUIDANCE TO ASSIGN SPDS AND VECTORS THAT AVOID RA ACTIVATION. THE RPTR STATED THE MANDATED SEPARATION IS SUCH IN IMC APCHS THAT RA ACTIVATION DOES NOT NORMALLY OCCUR AND/OR IS NOT A PROB. VISUALS ARE WHEN THE PROB OCCURS.

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.