Narrative:

At 4000 ft MSL on 11 mi right base for 35R ILS approach. TCASII TA alert then RA 'descend'. Vertical speed indicator commanded 2500 FPM down and showed traffic on nose level. Descended 500 ft to 3500 ft. TCASII showed 'clear of conflict' with traffic over top of us by 300 ft. Copilot told approach control as we initiated descent, they replied 'no traffic, turn to intercept localizer.' we suspect TCASII picked up an aircraft on left base for 36L parallel runway.

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Original NASA ASRS Text

Title: MLG ON 11 MI R BASE FOR 35 AT DFW. TCASII RA, SAME ALT, DIRECT AHEAD. CAPT DSNDED TO CLR RA.

Narrative: AT 4000 FT MSL ON 11 MI R BASE FOR 35R ILS APCH. TCASII TA ALERT THEN RA 'DSND'. VERT SPD INDICATOR COMMANDED 2500 FPM DOWN AND SHOWED TFC ON NOSE LEVEL. DSNDED 500 FT TO 3500 FT. TCASII SHOWED 'CLR OF CONFLICT' WITH TFC OVER TOP OF US BY 300 FT. COPLT TOLD APCH CTL AS WE INITIATED DSCNT, THEY REPLIED 'NO TFC, TURN TO INTERCEPT LOC.' WE SUSPECT TCASII PICKED UP AN ACFT ON L BASE FOR 36L PARALLEL RWY.

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.