Narrative:

Aircraft X was on approach when I noticed that his gear appeared up. I told him this; got no response and told him to 'go around gear appears up.' I then told him to enter left traffic for and to recycle his gear so that we could see if it comes down. When he was in a midfield downwind; I noticed we lost his transponder and told him so and asked if he was having any trouble with his equipment. I thought he said that he was having some alarms and that his fuel gauge was off. I asked him if he wanted to continue to hold or if he wanted to try and land. He told me he wanted to continue to hold; so I told him to continue in the traffic pattern and make a low approach and we would let him know if we see his gear.meanwhile; I was giving a briefing and there were multiple arrivals. Aircraft Y was on about a 3 mile final when I noticed that aircraft X was still in a base turn on a 90 degree intercept with aircraft Y. I issued a traffic alert and broke aircraft Y off of the approach. I did my best [to] vector the two aircraft away from each other and get aircraft Y back to a safe altitude. It appeared that the targets merged with about 100 feet of separation on the radar. It was very difficult to see aircraft X out the window because of some precipitation that was cluttering up the window so I didn't notice at first that he did not turn final.the pilot didn't do what he was told; but I should have issued the traffic to each pilot earlier than I did. I was giving a briefing at the time all of this happened as well so I was trying to scan through the checklist; equipment; etc.; as well as monitor the traffic and was just a little late on noticing aircraft X not doing what he was supposed to be doing.

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Original NASA ASRS Text

Title: SAT Tower Controllers reported a NMAC between a General Aviation aircraft experiencing difficulties and an air carrier.

Narrative: Aircraft X was on approach when I noticed that his gear appeared up. I told him this; got no response and told him to 'go around gear appears up.' I then told him to enter left traffic for and to recycle his gear so that we could see if it comes down. When he was in a midfield downwind; I noticed we lost his transponder and told him so and asked if he was having any trouble with his equipment. I thought he said that he was having some alarms and that his fuel gauge was off. I asked him if he wanted to continue to hold or if he wanted to try and land. He told me he wanted to continue to hold; so I told him to continue in the traffic pattern and make a low approach and we would let him know if we see his gear.Meanwhile; I was giving a briefing and there were multiple arrivals. Aircraft Y was on about a 3 mile final when I noticed that Aircraft X was still in a base turn on a 90 degree intercept with Aircraft Y. I issued a traffic alert and broke Aircraft Y off of the approach. I did my best [to] vector the two aircraft away from each other and get Aircraft Y back to a safe altitude. It appeared that the targets merged with about 100 feet of separation on the radar. It was very difficult to see Aircraft X out the window because of some precipitation that was cluttering up the window so I didn't notice at first that he did not turn final.The pilot didn't do what he was told; but I should have issued the traffic to each pilot earlier than I did. I was giving a briefing at the time all of this happened as well so I was trying to scan through the checklist; equipment; etc.; as well as monitor the traffic and was just a little late on noticing Aircraft X not doing what he was supposed to be doing.

Data retrieved from NASA's ASRS site 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.