Commercial Fixed Wing
Air Traffic Control Fully Certified
Confusion
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
ATC Equipment / Nav Facility / Buildings; Human Factors; Procedure
DFW TRACON was running dual ILS approaches into DFW and I was monitoring the Runway 17C final and DFW Tower's Local East 1 frequency. The Arrival Position (AR2) was being manned by a trainee and his trainer. I had to slow several aircraft near the Final Approach Fix and I believe that Air Carrier Y was 1 of them. This causes an accordion effect and instead of aircraft gradually slowing down; it's a kind of sudden slow down that you don't want to repeat over and over again due to the jerkiness of it; but 'there was training going on the Arrival 2 position'. Also we have a new 'STARS' program instead of 'ARTS' and data tags are different and we were getting some false targets due to different RADAR sites getting different readings and misreading transponder codes. I'll explain more later. VFR Guard Helicopter reported on the frequency and Tower gave him some advisories about Air Carrier Y (which was 2 miles away from him and pulling away plus about 2;000 FT above him). Then the VFR Guard Helicopter's data tag overlapped with Air Carrier X's so that I couldn't see Air Carrier X's speed and right then Tower started to give the VFR Guard Helicopter advisories about Air Carrier X while I noticed that Air Carrier Y had slowed down to 100 KTS less than 3 miles in front of Air Carrier X. Minimum separation at this point is 2.5 NM. I instructed Air Carrier X to slow down; I don't know if I said to 150 KTS or minimum approach speed but he was 60 KTS faster than Air Carrier Y and probably 2.7 miles in trail coming to the Final Approach Fix. I knew that Air Carrier Y wouldn't go any slower and his speed would pick up a little while Air Carrier X would now probably drop down to 110-100 KTS and that sending him around would be more dangerous than letting him continue so I let him continue. He landed but they were less than 2.5 NM apart pretty much from the FAF in. There are several things that can be fixed to make sure that this never happens again. I could have said 'screw it' and started slowing all of the planes earlier and let the arrival trainee 'deal with it' as this would have pushed his final out further. By doing that I would basically have to take over the DFW Tower's frequency and due to weather delays he was getting lots of 'what's my sequence' questions which of course tied up his frequency. STARS are definitely a work in progress and in many ways ARTS was/is better. Green data tags are of other aircraft that are not yours; which are white. ARTS had a better font and brightness settings than what STARS currently has! ARTS allowed different brightness settings for your white tags; other full data block green tags and limited data block green tags. STARS only allows different settings for white and green and the difference doesn't seem like much plus the STARS font is harder to read! In the 15 minutes before this incident we had no less that 3 'ghost' targets abeam aircraft on final for DFW. The display would all of a sudden show a transponder target beside an airliner on final. The 'ghost' would be at the same speed and altitude and usually his transponder code was off by 1 digit. This was explained to us as 'what another RADAR site was seeing' which is screwed up because when you work final monitor you have to check that all final monitors are on the same RADAR site! We were all on the West ASR9 at this time. We will get better acquainted with STARS as the years go by but I hope that the FAA doesn't think 'Mission Accomplished.'
D10 Controller described a loss of separation during dual ILS approaches. The reporter listed STARS equipment as contributing to the event.