Narrative:

Working local west assist (LWA1); the local West1 controller and I observed that an aircraft Y; still outside the FAF; for runway 36L; was encroaching upon four miles to aircraft X; who was inside the FAF. The local controller asked both aircraft their speeds because their indicated air speeds were 170 KTS and 120 KTS; respectively. After this exchange I was expecting the final monitor 3 (FM3) to slow the aircraft Y but there was no response; so I got on the land line and asked FM3 to slow the second aircraft and he did. As soon as I got off the line; I realized this just wasn't going to work and immediately re-coordinated with FM3 and asked him to break aircraft Y out and he began to do this when my flm; instructed me not to break the aircraft out. At first I hesitated; not understanding why I was told not to break the gaining aircraft out but upon the second time the supervisor told me this; I assumed he knew something I did not; for example that the aircraft is having some type of emergency and needs to land right away. Because time was critical; I did not query my supervisor about why he did not want the second aircraft pulled off the approach and instead complied with his instruction and asked FM3 not to break the aircraft out. I then told FM3 that we would try to establish visual separation; not really knowing or understanding what else to say to him under the circumstances. LW1 then asked the aircraft Y if he had the aircraft X in sight and the pilot said he was; and hearing this; FM3 pulled the aircraft off the approach. By this time; it appears that we may have lost separation but by what degree; I don't know. Recommendation; perhaps; there is some confusion here about pulling aircraft off the approach when they are outside the FAF; since at least twice in 2009 that I know of; there were operational deviations given to controllers; at dfw tower; who did this. However; in this case I was advising the FM3 to break the aircraft out; since I didn't think it would work and to try and save him from having an operational error. If the tower has to wait until the aircraft is over the FAF before we break them out then at what point are we liable for an operational error; if separation is lost prior to the FAF. Currently; we are working in a very precise environment of ATC where separation is measured by the foot; it seems and we cannot afford to wait until the aircraft is over the FAF before taking action. Additionally; there now seems to be added pressure from management not to break aircraft out too early due to recent go-arounds that may have been unnecessary. It has always been FAA policy to err on the side of safety; rather than to err on the side of efficiency and if this is new policy; we have not been briefed on it.

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Original NASA ASRS Text

Title: DFW Local Assist Controller described questionable wake turbulence event when Supervisor instructed the Local Controller allow two inbound aircraft to continue when separation was in doubt.

Narrative: Working Local West Assist (LWA1); the Local West1 Controller and I observed that an Aircraft Y; still outside the FAF; for Runway 36L; was encroaching upon four miles to Aircraft X; who was inside the FAF. The Local Controller asked both aircraft their speeds because their indicated air speeds were 170 KTS and 120 KTS; respectively. After this exchange I was expecting the Final Monitor 3 (FM3) to slow the Aircraft Y but there was no response; so I got on the land line and asked FM3 to slow the second aircraft and he did. As soon as I got off the line; I realized this just wasn't going to work and immediately re-coordinated with FM3 and asked him to break Aircraft Y out and he began to do this when my FLM; instructed me not to break the aircraft out. At first I hesitated; not understanding why I was told not to break the gaining aircraft out but upon the second time the Supervisor told me this; I assumed he knew something I did not; for example that the aircraft is having some type of emergency and needs to land right away. Because time was critical; I did not query my Supervisor about why he did not want the second aircraft pulled off the approach and instead complied with his instruction and asked FM3 not to break the aircraft out. I then told FM3 that we would try to establish visual separation; not really knowing or understanding what else to say to him under the circumstances. LW1 then asked the Aircraft Y if he had the Aircraft X in sight and the pilot said he was; and hearing this; FM3 pulled the aircraft off the approach. By this time; it appears that we may have lost separation but by what degree; I don't know. Recommendation; perhaps; there is some confusion here about pulling aircraft off the approach when they are outside the FAF; since at least twice in 2009 that I know of; there were Operational Deviations given to Controllers; at DFW Tower; who did this. However; in this case I was advising the FM3 to break the aircraft out; since I didn't think it would work and to try and save him from having an Operational Error. If the Tower has to wait until the aircraft is over the FAF before we break them out then at what point are we liable for an Operational Error; if separation is lost prior to the FAF. Currently; we are working in a very precise environment of ATC where separation is measured by the foot; it seems and we cannot afford to wait until the aircraft is over the FAF before taking action. Additionally; there now seems to be added pressure from management not to break aircraft out too early due to recent go-arounds that may have been unnecessary. It has always been FAA policy to err on the side of safety; rather than to err on the side of efficiency and if this is new policy; we have not been briefed on it.

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.