Narrative:

While tracking the localizer to dfw runway 31R on autoplt, we were given a descent clearance to 3000 ft from 5000 ft. We also were given a traffic call of an aircraft at our 10 O'clock position at 4500 ft. We told approach that we didn't have the traffic and approach told us that it was all right and that the traffic would maintain separation. We started down toward 3000 ft and the traffic on the TCASII went from 3 mi at 10 O'clock position to about 2 mi at about 9:30 O'clock position. At about 4700 ft we got an RA to climb at 1200-1500 FPM. We followed the RA back up to about 5300 ft when it stated clear of conflict. We informed approach that we had followed the RA and they reclred us to 3000 ft. We checked the TCASII traffic again and proceeded to 3000 ft without further incident to land on runway 31R. My concern is that the controller's assurances that the traffic would stay clear didn't hold true and if TCASII wouldn't have commanded a climb, this could have been a midair. We never saw the traffic. Unbriefed formation is a dangerous and unsatisfactory practice.

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Original NASA ASRS Text

Title: RPTR PERFORMS AN EVASIVE ACTION CLB AFTER RECEIVING A TCASII RA ON TFC WHICH CTLR CLAIMED WOULD MAINTAIN SEPARATION (FROM RPTR'S ACFT).

Narrative: WHILE TRACKING THE LOC TO DFW RWY 31R ON AUTOPLT, WE WERE GIVEN A DSCNT CLRNC TO 3000 FT FROM 5000 FT. WE ALSO WERE GIVEN A TFC CALL OF AN ACFT AT OUR 10 O'CLOCK POS AT 4500 FT. WE TOLD APCH THAT WE DIDN'T HAVE THE TFC AND APCH TOLD US THAT IT WAS ALL RIGHT AND THAT THE TFC WOULD MAINTAIN SEPARATION. WE STARTED DOWN TOWARD 3000 FT AND THE TFC ON THE TCASII WENT FROM 3 MI AT 10 O'CLOCK POS TO ABOUT 2 MI AT ABOUT 9:30 O'CLOCK POS. AT ABOUT 4700 FT WE GOT AN RA TO CLB AT 1200-1500 FPM. WE FOLLOWED THE RA BACK UP TO ABOUT 5300 FT WHEN IT STATED CLR OF CONFLICT. WE INFORMED APCH THAT WE HAD FOLLOWED THE RA AND THEY RECLRED US TO 3000 FT. WE CHKED THE TCASII TFC AGAIN AND PROCEEDED TO 3000 FT WITHOUT FURTHER INCIDENT TO LAND ON RWY 31R. MY CONCERN IS THAT THE CTLR'S ASSURANCES THAT THE TFC WOULD STAY CLR DIDN'T HOLD TRUE AND IF TCASII WOULDN'T HAVE COMMANDED A CLB, THIS COULD HAVE BEEN A MIDAIR. WE NEVER SAW THE TFC. UNBRIEFED FORMATION IS A DANGEROUS AND UNSATISFACTORY PRACTICE.

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.