Narrative:

Dfw airport was conducting instrument approaches to a north flow landing configuration due to a recent weather event. The ceilings were broken to overcast from rain showers that moved through the area. At varying times the departures were staggered off the airport for weather avoidance. The aircraft that made approaches subsequent to a B757 and MD80 had reported moderate chop and light to moderate rain on final to runway 36L. The final monitor position was open and providing final spacing control with override capability on tower frequency 124.15. As the B757 joined final I noticed his type and the trailing aircraft. I placed a four mile j-ring on the MD80 so I could monitor the spacing on final. I observed later that the spacing was decreasing so I asked the B757 for his indicated airspeed as well as the MD80's speed. Since the MD80 was outside of tower's airspace; I asked my local assist to call the final monitor and asked permission to slow the MD80 in D10's airspace. My local assist contacted the final monitor who slowed the MD80. The pilot did not initially respond to the speed reduction. As the aircraft neared the runway threshold spacing was diminishing and there was still an overtake occurring. My local assist told the final monitor that he had better break the MD80 out of the final. The tower supervisor immediately countermanded the control instruction which caught everyone in the tower by surprise. I allowed the aircraft to continue assuming the supervisor knew something I did not. Perhaps the MD80 was an emergency or critical fuel. I asked MD80 if he had the aircraft ahead in sight. The pilot's response was he was in IMC. By now I had explained the view on final to better discern the spacing between the B757 and the MD80; after I had received the IMC report from the MD80; the final monitor took corrective action and broke the MD80 off the approach with a left turn heading 220. I waited for the final monitor to change MD80 to approach for re-sequencing. Recommendation; one thing needs to be made explicit; there can be no waffling when it comes to separation. Either wake turbulence spacing needs to be a priority that controllers embrace and maintain; or the FAA policy needs to be amended to incorporate proximity event as a method of applying separation. It has always been my belief that wake turbulence separation should not be relaxed; amended; or fooled with. If a controller identifies a separation event that is immediate and needs to be addressed then that controller should do whatever is available to them to maintain or reestablish FAA separation criterion. Dfw tower is caught between a rock and a hard spot with the separation responsibility as it is applied between the tower and TRACON. When a controller identifies an event occurring and that aircraft is outside the FAF; which is outside of tower's jurisdiction; then he must first coordinate before taking action. Ninety-nine point nine percent of the time; TRACON and the final monitors do a good job of taking corrective action. However; there are times that the tower has prevented loss of separation by controlling first and coordinating later. This has led to some operational deviations being laid at the feet of those controllers that dare to step out and keep the separation. If the FAA has a policy that includes the acceptance of proximity events in lieu of separation then we need to better define this. Since final monitor has override capability; they can easily amend or overrule any control instruction that the tower might prematurely assign. After all; it is joint use airspace with separation responsibility designated to both tower and approach control. I have witnessed controllers being counseled for sending an aircraft around when in there opinion the separation was questionable. This has caused some controllers to be reticent when deciding how long they should wait to apply go-around procedures. I continue to apply what I have learned: safety is priorityone and above all else that is what the flying public expects from the FAA. If unwanted or unnecessary go-arounds are an agency concern; then perhaps the FAA can incorporate some of the distance measuring tools that is uses to determine separation criterion when it comes into question. Management has the ability to use hindsight and time to analyze an event and determine by precision if separation was compromised or not. The same tools should be at the disposal of controllers in real time. The only way a tower controller can base separation distance is by radar sweep and a j-ring. Although a benefit; it lacks the precision of dolr.

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Original NASA ASRS Text

Title: DFW controller described minimal wake separation event that resulted in the final monitor issuing go around instructions that subsequently resulted in a separation event.

Narrative: DFW airport was conducting instrument approaches to a North Flow landing configuration due to a recent weather event. The ceilings were broken to overcast from rain showers that moved through the area. At varying times the departures were staggered off the airport for weather avoidance. The aircraft that made approaches subsequent to A B757 and MD80 had reported moderate chop and light to moderate rain on final to Runway 36L. The Final Monitor position was open and providing final spacing control with override capability on tower frequency 124.15. As the B757 joined final I noticed his type and the trailing aircraft. I placed a four mile J-ring on the MD80 so I could monitor the spacing on final. I observed later that the spacing was decreasing so I asked the B757 for his indicated airspeed as well as the MD80's speed. Since the MD80 was outside of tower's airspace; I asked my Local Assist to call the Final Monitor and asked permission to slow the MD80 in D10's airspace. My Local Assist contacted the final monitor who slowed the MD80. The pilot did not initially respond to the speed reduction. As the aircraft neared the runway threshold spacing was diminishing and there was still an overtake occurring. My Local Assist told the Final Monitor that he had better break the MD80 out of the final. The tower supervisor immediately countermanded the control instruction which caught everyone in the tower by surprise. I allowed the aircraft to continue assuming the supervisor knew something I did not. Perhaps the MD80 was an emergency or critical fuel. I asked MD80 if he had the aircraft ahead in sight. The pilot's response was he was in IMC. By now I had explained the view on final to better discern the spacing between the B757 and the MD80; after I had received the IMC report from the MD80; the Final Monitor took corrective action and broke the MD80 off the approach with a left turn heading 220. I waited for the Final Monitor to change MD80 to Approach for re-sequencing. Recommendation; one thing needs to be made explicit; there can be no waffling when it comes to separation. Either wake turbulence spacing needs to be a priority that controllers embrace and maintain; or the FAA policy needs to be amended to incorporate proximity event as a method of applying separation. It has always been my belief that wake turbulence separation should not be relaxed; amended; or fooled with. If a controller identifies a separation event that is immediate and needs to be addressed then that controller should do whatever is available to them to maintain or reestablish FAA separation criterion. DFW Tower is caught between a rock and a hard spot with the separation responsibility as it is applied between the tower and TRACON. When a controller identifies an event occurring and that aircraft is outside the FAF; which is outside of tower's jurisdiction; then he must first coordinate before taking action. Ninety-nine point nine percent of the time; TRACON and the final monitors do a good job of taking corrective action. However; there are times that the tower has prevented loss of separation by controlling first and coordinating later. This has led to some operational deviations being laid at the feet of those controllers that dare to step out and keep the separation. If the FAA has a policy that includes the acceptance of proximity events in lieu of separation then we need to better define this. Since Final monitor has override capability; they can easily amend or overrule any control instruction that the tower might prematurely assign. After all; it is joint use airspace with separation responsibility designated to both tower and approach control. I have witnessed controllers being counseled for sending an aircraft around when in there opinion the separation was questionable. This has caused some controllers to be reticent when deciding how long they should wait to apply go-around procedures. I continue to apply what I have learned: safety is priorityone and above all else that is what the flying public expects from the FAA. If unwanted or unnecessary go-arounds are an agency concern; then perhaps the FAA can incorporate some of the distance measuring tools that is uses to determine separation criterion when it comes into question. Management has the ability to use hindsight and time to analyze an event and determine by precision if separation was compromised or not. The same tools should be at the disposal of controllers in real time. The only way a tower controller can base separation distance is by RADAR sweep and a J-Ring. Although a benefit; it lacks the precision of DOLR.

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.