Narrative:

Into dfw, aircraft was being vectored for a visual approach to runway 17L at dfw. WX conditions were VFR, but sun and haze at dusk made visibility difficult. ATC frequency was busy due to numerous aircraft arriving at dfw. The captain was flying and began to slow and configure the aircraft at 15 mi from dfw. Altitude was 5000 ft MSL, speed 250 KTS. ATC asked the crew if the airport was in sight. It was not, due to haze. The ATC frequency became busy and the crew continued on a westerly heading. The airport became visible as the aircraft passed abeam the approach end of runway 17L. Simultaneously, ATC gave the crew a 90 degree turn south, with the instructions to slow to 170 KTS, and cleared the visual approach to runway 17L. As the aircraft was in a tight turn to the left, leaving 2800 ft MSL, TCASII issued a mandatory 'climb now' alert. Due to the aircraft's attitude, and low visibility, the captain immediately began to climb. ATC was notified, and they acknowledged the report. ATC asked if the runway was still in sight, then reclred the crew for the visual approach to runway 17L. The aircraft was now at 3800 ft MSL, and the TCASII issued the 'clear of conflict' alert. The captain intercepted the approach path for runway 17L, and made a normal landing. Cause of incident: factors included low visibility, excess speed, and TCASII alert. Recommendations: increased traffic separation during marginal VFR approachs. All major airports should standardize on speed control for aircraft separation during approach. TCASII procedures should be adapted to compensate further for dense traffic in parallel approach environment.

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Original NASA ASRS Text

Title: FLC OF AN ACR MLG ACFT DEVIATED FROM ASSIGNED DSCNT ALT IN RESPONSE TO A TCASII RA.

Narrative: INTO DFW, ACFT WAS BEING VECTORED FOR A VISUAL APCH TO RWY 17L AT DFW. WX CONDITIONS WERE VFR, BUT SUN AND HAZE AT DUSK MADE VISIBILITY DIFFICULT. ATC FREQ WAS BUSY DUE TO NUMEROUS ACFT ARRIVING AT DFW. THE CAPT WAS FLYING AND BEGAN TO SLOW AND CONFIGURE THE ACFT AT 15 MI FROM DFW. ALT WAS 5000 FT MSL, SPD 250 KTS. ATC ASKED THE CREW IF THE ARPT WAS IN SIGHT. IT WAS NOT, DUE TO HAZE. THE ATC FREQ BECAME BUSY AND THE CREW CONTINUED ON A WESTERLY HDG. THE ARPT BECAME VISIBLE AS THE ACFT PASSED ABEAM THE APCH END OF RWY 17L. SIMULTANEOUSLY, ATC GAVE THE CREW A 90 DEG TURN S, WITH THE INSTRUCTIONS TO SLOW TO 170 KTS, AND CLRED THE VISUAL APCH TO RWY 17L. AS THE ACFT WAS IN A TIGHT TURN TO THE L, LEAVING 2800 FT MSL, TCASII ISSUED A MANDATORY 'CLB NOW' ALERT. DUE TO THE ACFT'S ATTITUDE, AND LOW VISIBILITY, THE CAPT IMMEDIATELY BEGAN TO CLB. ATC WAS NOTIFIED, AND THEY ACKNOWLEDGED THE RPT. ATC ASKED IF THE RWY WAS STILL IN SIGHT, THEN RECLRED THE CREW FOR THE VISUAL APCH TO RWY 17L. THE ACFT WAS NOW AT 3800 FT MSL, AND THE TCASII ISSUED THE 'CLR OF CONFLICT' ALERT. THE CAPT INTERCEPTED THE APCH PATH FOR RWY 17L, AND MADE A NORMAL LNDG. CAUSE OF INCIDENT: FACTORS INCLUDED LOW VISIBILITY, EXCESS SPD, AND TCASII ALERT. RECOMMENDATIONS: INCREASED TFC SEPARATION DURING MARGINAL VFR APCHS. ALL MAJOR ARPTS SHOULD STANDARDIZE ON SPD CTL FOR ACFT SEPARATION DURING APCH. TCASII PROCS SHOULD BE ADAPTED TO COMPENSATE FURTHER FOR DENSE TFC IN PARALLEL APCH ENVIRONMENT.

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.