Narrative:

On the bonham five arrival on vectors from karla at 5000 ft. Heading wsw towards the runway 17C localizer about 26 DME nne of dfw. ATC called out traffic to us at 1 to 2 o'clock 5 miles level at 4000 ft. The first officer spotted the jet traffic at 4000 ft and also stated later he saw some additional traffic. I could see the 4000 ft jet traffic also. I then looked inside at the TCAS and saw the traffic was showing only 800 ft below us. I checked our altimeters and we were level at 5000 ft and the autopilot was on. Simultaneously I was looking at the first officer looking at the traffic and he started gesturing to climb as I heard the RA for a climb I executed the RA procedure. I was wondering why the traffic was climbing up underneath us. As I'm passing 5000 ft ATC wanted to know if we could level at 6000 ft; which we complied with; and asking why the traffic below us was climbed towards us and he stated that the traffic was climbing and also reacting to a TCAS RA. Afterwards we were vectored for the ILS runway 17C and a normal landing at dfw. When I received the climb from the TCAS and looked down at the vsi it was red through 2000 vsi up. After landing I called the dfw tracon and talked to the supervisor on duty to discuss the event. He stated that both the gulfstream traffic and our aircraft responded to RA's as trained. It was all caused by traffic at 3900 ft squawking 1200 VFR and not working any approach controller just 100 ft below the floor of the class B. The supervisor mentioned they were still tracking the aircraft and the gulfstream below us never got higher than 4800 ft.

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Original NASA ASRS Text

Title: Air carrier flight crew experienced a TCAS RA while on vectors for a south landing at DFW. The RA was caused by a Gulfstream below who in turn was responding to an RA caused by VFR traffic just below the floor of the Class B.

Narrative: On the Bonham Five Arrival on vectors from KARLA at 5000 FT. Heading WSW towards the Runway 17C localizer about 26 DME NNE of DFW. ATC called out traffic to us at 1 to 2 o'clock 5 miles level at 4000 FT. The First Officer spotted the jet traffic at 4000 FT and also stated later he saw some additional traffic. I could see the 4000 FT jet traffic also. I then looked inside at the TCAS and saw the traffic was showing only 800 FT below us. I checked our altimeters and we were level at 5000 FT and the autopilot was on. Simultaneously I was looking at the First Officer looking at the traffic and he started gesturing to climb as I heard the RA for a climb I executed the RA procedure. I was wondering why the traffic was climbing up underneath us. As I'm passing 5000 FT ATC wanted to know if we could level at 6000 FT; which we complied with; and asking why the traffic below us was climbed towards us and he stated that the traffic was climbing and also reacting to a TCAS RA. Afterwards we were vectored for the ILS Runway 17C and a normal landing at DFW. When I received the climb from the TCAS and looked down at the VSI it was red through 2000 VSI up. After landing I called the DFW Tracon and talked to the Supervisor on duty to discuss the event. He stated that both the Gulfstream traffic and our aircraft responded to RA's as trained. It was all caused by traffic at 3900 FT squawking 1200 VFR and not working any Approach Controller just 100 FT below the floor of the Class B. The Supervisor mentioned they were still tracking the aircraft and the Gulfstream below us never got higher than 4800 FT.

Data retrieved from NASA's ASRS site as of April 2012 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.