Narrative:

After contacting regional approach ATC instructed air carrier X to turn to a 280 degree heading at the 5 DME/296 degree fix off of scurry VOR. ATC told us to descend from 11000 to 5000. Just south of navy dallas, captain and I were concerned about lack of sequencing instructions for runway 35R. Therefore, I started to slow from 250 KIAS. While slowing through 210 KIAS, ATC instructed us to slow to 190 KIAS and then descend to 3000. ATC instructed us to turn right to 310 degrees and look for an large transport on a high right base descending out of 4500 MSL. We told ATC we had the aircraft but questioned our separation as he was approximately 3 mi out on TCASII. We were cleared for the visual to runway 35R but told to maintain 170 KIAS until the OM. After encountering significant wake turbulence, captain and I decided to reduce to 150 KIAS. Approach control was so busy, we were unable to break in and inform ATC of our speed reduction. Shortly thereafter, ATC (approach control) questioned our airspeed. We stated we had slowed to final approach speed. The final monitor came on and asked 'what speed is that' and we replied 150 KIAS, and had slowed as we were following an large transport. Approach control snapped back and said 'you only needed 3 mi separation.' during this brief conversation we had passed the OM. Upon landing the large transport had only cleared when we were less than 200 ft AGL. Had we not reduced our airspeed, a go around would have occurred! This problem arose from poor aircraft sequencing, along with the fact that the large transport overshot the final to runway 35R, and then slowed, affecting our operation. This, combined with an overcrowded approach control, led to this sequencing problem.

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Original NASA ASRS Text

Title: ACR X UNAUTH SPD REDUCTION USED TCASII FOR SPACING. PLTDEV.

Narrative: AFTER CONTACTING REGIONAL APCH ATC INSTRUCTED ACR X TO TURN TO A 280 DEG HDG AT THE 5 DME/296 DEG FIX OFF OF SCURRY VOR. ATC TOLD US TO DSND FROM 11000 TO 5000. JUST S OF NAVY DALLAS, CAPT AND I WERE CONCERNED ABOUT LACK OF SEQUENCING INSTRUCTIONS FOR RWY 35R. THEREFORE, I STARTED TO SLOW FROM 250 KIAS. WHILE SLOWING THROUGH 210 KIAS, ATC INSTRUCTED US TO SLOW TO 190 KIAS AND THEN DSND TO 3000. ATC INSTRUCTED US TO TURN R TO 310 DEGS AND LOOK FOR AN LGT ON A HIGH R BASE DSNDING OUT OF 4500 MSL. WE TOLD ATC WE HAD THE ACFT BUT QUESTIONED OUR SEPARATION AS HE WAS APPROX 3 MI OUT ON TCASII. WE WERE CLRED FOR THE VISUAL TO RWY 35R BUT TOLD TO MAINTAIN 170 KIAS UNTIL THE OM. AFTER ENCOUNTERING SIGNIFICANT WAKE TURB, CAPT AND I DECIDED TO REDUCE TO 150 KIAS. APCH CTL WAS SO BUSY, WE WERE UNABLE TO BREAK IN AND INFORM ATC OF OUR SPD REDUCTION. SHORTLY THEREAFTER, ATC (APCH CTL) QUESTIONED OUR AIRSPD. WE STATED WE HAD SLOWED TO FINAL APCH SPD. THE FINAL MONITOR CAME ON AND ASKED 'WHAT SPD IS THAT' AND WE REPLIED 150 KIAS, AND HAD SLOWED AS WE WERE FOLLOWING AN LGT. APCH CTL SNAPPED BACK AND SAID 'YOU ONLY NEEDED 3 MI SEPARATION.' DURING THIS BRIEF CONVERSATION WE HAD PASSED THE OM. UPON LNDG THE LGT HAD ONLY CLRED WHEN WE WERE LESS THAN 200 FT AGL. HAD WE NOT REDUCED OUR AIRSPD, A GAR WOULD HAVE OCCURRED! THIS PROB AROSE FROM POOR ACFT SEQUENCING, ALONG WITH THE FACT THAT THE LGT OVERSHOT THE FINAL TO RWY 35R, AND THEN SLOWED, AFFECTING OUR OP. THIS, COMBINED WITH AN OVERCROWDED APCH CTL, LED TO THIS SEQUENCING PROB.

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.