Narrative:

Air carrier X level at 4000 ft MLS, 210 KTS assigned airspeed, 270 degree heading assigned by approach control, autoplt engaged, vectors being given were to vector aircraft on to localizer to runway 35R at dfw airport (GS was inoperative), aircraft was southeast of dfw airport approximately 14 mi. Air carrier X was given a 170 degree heading assignment by approach. Aircraft was started in a turn to that direction but apparently this rate of turn was insufficient to avoid a traffic conflict. Aircraft was in the clouds at the time and could not provide it's own traffic separation. At the time an approach supervisor took over (change in voice) and gave an 'immediate turn to 170 degree heading.' aircraft autoplt was disconnected at this time and aircraft was rolled into a 45 degree angle of bank at an accelerated roll rate than the autoplt could have provided. At this same time air carrier X broke out of the clouds and aircraft Y could be seen in front of ours approximately 2.5 mi directly in front. We passed behind this aircraft and then were given a 020 degree heading assignment and speed reduction to 170 KTS by approach control. This vector was to vector aircraft back to the localizer inbound course for an approach into dfw airport. Still being too close in trail to the other aircraft in front of ours on the localizer approach we were given a turn to the east and vectored back around for another approach. During the evasive maneuvers with autoplt disconnected our aircraft descended to 3600 ft MSL. The aircraft was immediately returned to 4000 ft assigned altitude and autoplt engaged. Altitude loss was due to steep angles of bank, changing aircraft performance (speed reduction), and primary attention being given to conflict aircraft.

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Original NASA ASRS Text

Title: ACR X HAD LTSS FROM ACFT Y. SYS ERROR. ACR X NON ADHERENCE TO ATC CLRNC (UNAUTH DSCNT FROM ASSIGNED ALT). PLT DEV.

Narrative: ACR X LEVEL AT 4000 FT MLS, 210 KTS ASSIGNED AIRSPD, 270 DEG HDG ASSIGNED BY APCH CTL, AUTOPLT ENGAGED, VECTORS BEING GIVEN WERE TO VECTOR ACFT ON TO LOC TO RWY 35R AT DFW ARPT (GS WAS INOP), ACFT WAS SE OF DFW ARPT APPROX 14 MI. ACR X WAS GIVEN A 170 DEG HDG ASSIGNMENT BY APCH. ACFT WAS STARTED IN A TURN TO THAT DIRECTION BUT APPARENTLY THIS RATE OF TURN WAS INSUFFICIENT TO AVOID A TFC CONFLICT. ACFT WAS IN THE CLOUDS AT THE TIME AND COULD NOT PROVIDE IT'S OWN TFC SEPARATION. AT THE TIME AN APCH SUPVR TOOK OVER (CHANGE IN VOICE) AND GAVE AN 'IMMEDIATE TURN TO 170 DEG HDG.' ACFT AUTOPLT WAS DISCONNECTED AT THIS TIME AND ACFT WAS ROLLED INTO A 45 DEG ANGLE OF BANK AT AN ACCELERATED ROLL RATE THAN THE AUTOPLT COULD HAVE PROVIDED. AT THIS SAME TIME ACR X BROKE OUT OF THE CLOUDS AND ACFT Y COULD BE SEEN IN FRONT OF OURS APPROX 2.5 MI DIRECTLY IN FRONT. WE PASSED BEHIND THIS ACFT AND THEN WERE GIVEN A 020 DEG HDG ASSIGNMENT AND SPD REDUCTION TO 170 KTS BY APCH CTL. THIS VECTOR WAS TO VECTOR ACFT BACK TO THE LOC INBOUND COURSE FOR AN APCH INTO DFW ARPT. STILL BEING TOO CLOSE IN TRAIL TO THE OTHER ACFT IN FRONT OF OURS ON THE LOC APCH WE WERE GIVEN A TURN TO THE E AND VECTORED BACK AROUND FOR ANOTHER APCH. DURING THE EVASIVE MANEUVERS WITH AUTOPLT DISCONNECTED OUR ACFT DSNDED TO 3600 FT MSL. THE ACFT WAS IMMEDIATELY RETURNED TO 4000 FT ASSIGNED ALT AND AUTOPLT ENGAGED. ALT LOSS WAS DUE TO STEEP ANGLES OF BANK, CHANGING ACFT PERFORMANCE (SPD REDUCTION), AND PRIMARY ATTN BEING GIVEN TO CONFLICT ACFT.

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.