Narrative:

We were on vectors with approach control over the vicinity of frisco or the colony; kind of on a long extended base leg; for an expected ILS to 17C. Frequency 127.05. We were given clearance to descend to 5000 ft. In the descent; at roughly 6500 ft; perhaps; we got a TA and the yellow traffic indicator at 12 o'clock. We could not spot the traffic initially. At about 6000 ft still in the descent; we got the RA and the red traffic indicator at 12 o'clock; plus new flight path guidance to climb. At that point; the relief pilot identified the traffic straight ahead and said it looked to be an experimental airplane. I disconnected the automation and hand flew the airplane in accordance with the RA instructions; which directed a climb. I smoothly climbed straight ahead to about 6500 ft or 7000 ft; roughly; the captain (pilot monitoring) notified ATC of the RA; and I returned to the original altitude and airspeed once we were clear of conflict. On the ground; at the gate; the captain planned to notify dispatch. I believe we came within 500 ft of the traffic; or possibly closer; which I think was at 5500 ft at the time.when we reported the RA to the ATC controller; she said in response that she has that traffic on TCAS; or on her radar; or something to that effect. My thought was; 'then why were we on vectors descending into it?'

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Original NASA ASRS Text

Title: An air carrier crew on vectors to DFW Runway 17C and descending to 5;000 ft followed a TCAS RA from an aircraft at 5;500 ft. The aircraft was in Class B; known to ATC but not reported to the pilots prior to the TCAS alert.

Narrative: We were on vectors with Approach Control over the vicinity of Frisco or The Colony; kind of on a long extended base leg; for an expected ILS to 17C. Frequency 127.05. We were given clearance to descend to 5000 ft. In the descent; at roughly 6500 ft; perhaps; we got a TA and the yellow traffic indicator at 12 o'clock. We could not spot the traffic initially. At about 6000 ft still in the descent; we got the RA and the red traffic indicator at 12 o'clock; plus new flight path guidance to climb. At that point; the Relief Pilot identified the traffic straight ahead and said it looked to be an experimental airplane. I disconnected the automation and hand flew the airplane in accordance with the RA instructions; which directed a climb. I smoothly climbed straight ahead to about 6500 ft or 7000 ft; roughly; the Captain (pilot monitoring) notified ATC of the RA; and I returned to the original altitude and airspeed once we were Clear of Conflict. On the ground; at the gate; the captain planned to notify Dispatch. I believe we came within 500 ft of the traffic; or possibly closer; which I think was at 5500 ft at the time.When we reported the RA to the ATC Controller; she said in response that she has that traffic on TCAS; or on her radar; or something to that effect. My thought was; 'Then why were we on vectors descending into it?'

Data retrieved from NASA's ASRS site 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.