Narrative:

While working the combined positions of radar west (rw); radar east (re); radar south (rs) and finals (af) at aus ATCT; aircraft X (P32R) was handed off to aus from grk arac at 6;000 MSL as an inbound to aus. Once aircraft X; a saratoga; was in my airspace I asked them to continue direct to the airport as a vector to a visual approach to runway 17L and allowed them to descend at pilot's discretion to 4;000 MSL. Just a few minutes later; aircraft Y (DC9) was handed off to aus from ZHU ARTCC while descending to 13;000 MSL; also an inbound to land at kaus. At this point aircraft X was approximately 25 miles north northeast; headed south southwest and indicating 120 KTS; while aircraft Y was about 45 miles north; headed south and indicating 350 KTS. Aircraft Y informed me they were landing at an FBO on our east side so I told them to expect a visual approach to runway 17L. Their overtake should have had them past aircraft X before either was 15 miles from the field. The night sky was referred to by pilots; as 'clear and a million.' I informed aircraft Y of the saratoga traffic ahead of them and by 20 miles out they had that traffic in sight. I advised them to maintain visual separation with the saratoga and they agreed to. Knowing that the DC9 would overfly the smaller aircraft and potentially lose sight of them I also had the saratoga looking for the DC9. With the DC9 still 2 to 3 miles behind the saratoga; and 2;000 ft plus above them; the saratoga reported seeing the DC9. I issued instructions for the saratoga to maintain visual separation from the DC9 and follow them to the airport; cleared for the visual approach to runway 17L with a caution for the wake turbulence of the passing jet. Aircraft X agreed to maintain visual separation and follow the DC9 on visual approach. At 15 miles from kaus; the DC9 was about a mile behind the PA32 and still was indicating 240 KTS. Then I noticed the jet descending on the saratoga and I advised aircraft X to 'maneuver as necessary' because 'the jet appears to be dropping on you.' aircraft X nonchalantly agreed to do whatever was needed. I specifically chose not to administer any further control instructions to either aircraft because doing so may have placed either one of them; or both; in a more hazardous situation. At 12 miles out I watched in amazement as the jet's altitude readout showed 2;700 MSL; the last altitude I'd seen on the saratoga which was now merged with the DC9. Aircraft Y reported losing sight of the other guy and receiving an RA while they were together. I did not see any indication of an attempt to climb from the DC9. My response to the DC9 pilot was that the saratoga 'appears to be a little behind you now and about 100 ft below.' I then switch aircraft Y to the tower frequency. Right after they acknowledged the communications switch I apologized to aircraft X for the DC9 'dropping on you like that.' the saratoga said it wasn't an issue because they had them in sight the whole time. I again told them to be cautious of the wake turbulence and transferred them to the tower frequency also. By an 8-mile final I noticed that the jet had slowed so much that the saratoga had to reduce speed to stay safely behind them. I relayed my surprise in an override comment to the tower controller. These were the only two aircraft in my airspace at the time. In retrospect; I certainly didn't need to have the DC9 land on runway 17L. I could have set them up for runway 17R instead. That act alone would have prevented this from being an issue. My concern is that this DC9 pilot knew that another aircraft was out there; saw them; descended to the same altitude as the traffic; lost sight of them; received a TCAS alert; and still continued to drop without knowing where the traffic now was. I believe everything was in accordance with applicable directives; but this was an extremely unsafe encounter. Later; aircraft X was departing aus on an IFR flight when I asked them 'how close was that earlier?'they responded that it was less than they would have liked; but not a big deal. They also said that they turned 15 degrees. My conclusions in regard to this event are as follows: 1. I should not show a runway-bias by simply allowing an arrival to get the runway that is closest to their parking location. 2. I need to issue definitive directions/instructions to better 'control' the situation that is developing. 3. I need to rely on my inner 'safety gut check' and break the speed/expediency override desire. Other than that I don't really know what I might do differently next time.

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Original NASA ASRS Text

Title: AUS Approach Controller described a potential conflict event involving two arrival aircraft that were maintaining visual separation; the reporter noting inaction on their part as a contributing factor.

Narrative: While working the combined positions of RADAR West (RW); RADAR East (RE); RADAR South (RS) and Finals (AF) at AUS ATCT; Aircraft X (P32R) was handed off to AUS from GRK ARAC at 6;000 MSL as an inbound to AUS. Once Aircraft X; a Saratoga; was in my airspace I asked them to continue direct to the airport as a vector to a Visual Approach to Runway 17L and allowed them to descend at pilot's discretion to 4;000 MSL. Just a few minutes later; Aircraft Y (DC9) was handed off to AUS from ZHU ARTCC while descending to 13;000 MSL; also an inbound to land at KAUS. At this point Aircraft X was approximately 25 miles north northeast; headed south southwest and indicating 120 KTS; while Aircraft Y was about 45 miles north; headed south and indicating 350 KTS. Aircraft Y informed me they were landing at an FBO on our east side so I told them to expect a Visual Approach to Runway 17L. Their overtake should have had them past Aircraft X before either was 15 miles from the field. The night sky was referred to by pilots; as 'clear and a million.' I informed Aircraft Y of the Saratoga traffic ahead of them and by 20 miles out they had that traffic in sight. I advised them to maintain visual separation with the Saratoga and they agreed to. Knowing that the DC9 would overfly the smaller aircraft and potentially lose sight of them I also had the Saratoga looking for the DC9. With the DC9 still 2 to 3 miles behind the Saratoga; and 2;000 FT plus above them; the Saratoga reported seeing the DC9. I issued instructions for the Saratoga to maintain visual separation from the DC9 and follow them to the airport; cleared for the Visual Approach to Runway 17L with a caution for the Wake Turbulence of the passing jet. Aircraft X agreed to maintain visual separation and follow the DC9 on visual approach. At 15 miles from KAUS; the DC9 was about a mile behind the PA32 and still was indicating 240 KTS. Then I noticed the jet descending on the Saratoga and I advised Aircraft X to 'maneuver as necessary' because 'the jet appears to be dropping on you.' Aircraft X nonchalantly agreed to do whatever was needed. I specifically chose not to administer any further control instructions to either aircraft because doing so may have placed either one of them; or both; in a more hazardous situation. At 12 miles out I watched in amazement as the jet's altitude readout showed 2;700 MSL; the last altitude I'd seen on the Saratoga which was now merged with the DC9. Aircraft Y reported losing sight of the other guy and receiving an RA while they were together. I did not see any indication of an attempt to climb from the DC9. My response to the DC9 pilot was that the Saratoga 'appears to be a little behind you now and about 100 FT below.' I then switch Aircraft Y to the Tower frequency. Right after they acknowledged the communications switch I apologized to Aircraft X for the DC9 'dropping on you like that.' The Saratoga said it wasn't an issue because they had them in sight the whole time. I again told them to be cautious of the wake turbulence and transferred them to the Tower frequency also. By an 8-mile final I noticed that the jet had slowed so much that the Saratoga had to reduce speed to stay safely behind them. I relayed my surprise in an override comment to the Tower Controller. These were the only two aircraft in my airspace at the time. In retrospect; I certainly didn't need to have the DC9 land on Runway 17L. I could have set them up for Runway 17R instead. That act alone would have prevented this from being an issue. My concern is that this DC9 pilot knew that another aircraft was out there; saw them; descended to the same altitude as the traffic; lost sight of them; received a TCAS alert; and still continued to drop without knowing where the traffic now was. I believe everything was in accordance with applicable directives; but this was an extremely unsafe encounter. Later; Aircraft X was departing AUS on an IFR flight when I asked them 'how close was that earlier?'They responded that it was less than they would have liked; but not a big deal. They also said that they turned 15 degrees. My conclusions in regard to this event are as follows: 1. I should not show a runway-bias by simply allowing an arrival to get the runway that is closest to their parking location. 2. I need to issue definitive directions/instructions to better 'control' the situation that is developing. 3. I need to rely on my inner 'safety gut check' and break the speed/expediency override desire. Other than that I don't really know what I might do differently next time.

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.