Narrative:

We were being vectored to the ILS 13R off the boids arrival to dfw in a large transport aircraft. Traffic was very heavy and the controller was very busy. At 8000', we received a heading and were cleared to 3500'. In the descent, we were asked to slow to 170 KTS. The first officer was flying the aircraft with the autoplt using the MCP to program. Upon selecting a speed of 170 KTS, the aircraft leveled off too slow. Approach control advised us of crossing traffic at 6000', two O'clock at a range I can't recall (8-10 mi). He was busy and came back shortly and asked us to expedite through 5000', again reporting the traffic conflict. The large transport is difficult to get down, especially in a go down, slow down and the first officer seemed at first confused about how to manage the MCP best to comply with the speed and altitude requirement. He was using the vertical speed mode to slow his descent to reach the requested speed and when he heard the call to expedite descent, he deployed spdbrakes, called for flaps to 15 degree and forgot the MCP was in vertical speed, therefore got no increase in descent rate. Actually the autothrottle added power to maintain selected speed at his selected vertical speed. At this time we were hung up at just below 6000' and the ctrl gave us a hard turn to avoid the conflict. The first officer realized that more prompt action was needed, I had twice already told him to get it down, and I was about to take the aircraft, when he turned off the autoplt, pushed it over manually and initiated the turn. We got a TCAS ii 'traffic' call at 5000' and approximately 1 NM from traffic, followed by ATC reversing our turn back to an ILS intercept. I was involved tuning ILS frequencys, setting up navaids and completing the approach checklist. We were victims of a busy traffic environment, a controller who was put in the situation by our being too slow to respond to his advisories and a workload of a two man crew in an automated aircraft that was slow to respond to command conflicts it could not resolve. The first officer is very competent and I let this lull me to not recognize his confusion earlier. We both have about a yr on this type aircraft, are both pretty adept using this equipment but were just slow enough to contribute to this situation. We also fly widebody transport type a, B, and C along with the large transport.

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Original NASA ASRS Text

Title: ACR LGT WAS SLOW TO RESPOND TO CLRNC TO GET DOWN AND SLOW DOWN RESULTING IN LESS THAN LEGAL SEPARATION.

Narrative: WE WERE BEING VECTORED TO THE ILS 13R OFF THE BOIDS ARR TO DFW IN A LGT ACFT. TFC WAS VERY HVY AND THE CTLR WAS VERY BUSY. AT 8000', WE RECEIVED A HDG AND WERE CLRED TO 3500'. IN THE DSNT, WE WERE ASKED TO SLOW TO 170 KTS. THE F/O WAS FLYING THE ACFT WITH THE AUTOPLT USING THE MCP TO PROGRAM. UPON SELECTING A SPD OF 170 KTS, THE ACFT LEVELED OFF TOO SLOW. APCH CTL ADVISED US OF XING TFC AT 6000', TWO O'CLOCK AT A RANGE I CAN'T RECALL (8-10 MI). HE WAS BUSY AND CAME BACK SHORTLY AND ASKED US TO EXPEDITE THROUGH 5000', AGAIN RPTING THE TFC CONFLICT. THE LGT IS DIFFICULT TO GET DOWN, ESPECIALLY IN A GO DOWN, SLOW DOWN AND THE F/O SEEMED AT FIRST CONFUSED ABOUT HOW TO MANAGE THE MCP BEST TO COMPLY WITH THE SPD AND ALT REQUIREMENT. HE WAS USING THE VERT SPD MODE TO SLOW HIS DSNT TO REACH THE REQUESTED SPD AND WHEN HE HEARD THE CALL TO EXPEDITE DSNT, HE DEPLOYED SPDBRAKES, CALLED FOR FLAPS TO 15 DEG AND FORGOT THE MCP WAS IN VERT SPD, THEREFORE GOT NO INCREASE IN DSNT RATE. ACTUALLY THE AUTOTHROTTLE ADDED PWR TO MAINTAIN SELECTED SPD AT HIS SELECTED VERT SPD. AT THIS TIME WE WERE HUNG UP AT JUST BELOW 6000' AND THE CTRL GAVE US A HARD TURN TO AVOID THE CONFLICT. THE F/O REALIZED THAT MORE PROMPT ACTION WAS NEEDED, I HAD TWICE ALREADY TOLD HIM TO GET IT DOWN, AND I WAS ABOUT TO TAKE THE ACFT, WHEN HE TURNED OFF THE AUTOPLT, PUSHED IT OVER MANUALLY AND INITIATED THE TURN. WE GOT A TCAS II 'TFC' CALL AT 5000' AND APPROX 1 NM FROM TFC, FOLLOWED BY ATC REVERSING OUR TURN BACK TO AN ILS INTERCEPT. I WAS INVOLVED TUNING ILS FREQS, SETTING UP NAVAIDS AND COMPLETING THE APCH CHKLIST. WE WERE VICTIMS OF A BUSY TFC ENVIRONMENT, A CTLR WHO WAS PUT IN THE SITUATION BY OUR BEING TOO SLOW TO RESPOND TO HIS ADVISORIES AND A WORKLOAD OF A TWO MAN CREW IN AN AUTOMATED ACFT THAT WAS SLOW TO RESPOND TO COMMAND CONFLICTS IT COULD NOT RESOLVE. THE F/O IS VERY COMPETENT AND I LET THIS LULL ME TO NOT RECOGNIZE HIS CONFUSION EARLIER. WE BOTH HAVE ABOUT A YR ON THIS TYPE ACFT, ARE BOTH PRETTY ADEPT USING THIS EQUIP BUT WERE JUST SLOW ENOUGH TO CONTRIBUTE TO THIS SITUATION. WE ALSO FLY WDB TYPE A, B, AND C ALONG WITH THE LGT.

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.