Narrative:

While flying the braun 2 STAR with an expected visual approach to 13R into sat; ATC turned our base leg just prior to jatax. We were given a heading; an altitude of 4;000 feet clearance and ATC pointed out traffic to follow at 10 o'clock; which we called traffic in sight. We were cleared for a visual approach when right at the same moment ATC issued a new traffic advisory for an aircraft they were not in communication with. He started out 1;000 feet below and climbing. We got a TA; and I stated to my first officer whom was pilot flying to be prepared for an RA as it was not looking very promising.ATC gave us instructions to do whatever we needed to do to avoid the traffic; which we did not have in sight at the time. Just as ATC gave us this command; the TA turned into a descend RA. We initiated a descent. This aircraft was apparently on departure out of a nearby satellite airport and was climbing out. We got two descend RA aural alerts when the collision avoidance switched to a climb; climb now aural alert. We immediately changed course and complied with the new RA instructions. We had a jump seater who was commuting home and was familiar with the area. He later stated he did have the traffic in sight during the RA and it appeared to be less than a mile in a 45-degree bank turning away in a climb. Once the RA was resolved; we were in a position to still make a safe landing at sat and continued the approach. ATC stated they have had numerous issues with aircraft departing out of this satellite airport and have filed numerous reports but nothing has changed.the cause appears to be conflicting traffic patterns between 5c1 airport and sat. Looking at the airspace charts; the king air was technically within class east airspace as were we. We may have been just right on the outside ring of the class C. With a light payload the king air must have been climbing at a highly unusual rate or maybe a missed go-around from a previous landing attempt but either way proved to be a conflict with our base turn which had us just on the inside of hasdo. As frustrating as the situation was within the current definitions of airspace around sat it appears there was no airspace incursions and was just a chance encounter. It appears to be a standard issues with aircraft departing out of 5c1.suggestions: outside of redefining airspace in the local area; this exact situation will likely continue to happen. With two aircraft in high workload phases of flight; this could definitely cause a major issue in the future. Maybe changing the traffic pattern direction out of 5c1 to a right hand pattern would minimize issues. However; I will continue to be more vigilant on approach into sat when we are forced to extend our downwind outside of the class C and I would hope that departing VFR traffic out of 5c1 may elect to get flight following prior to departure (if local ATC offers it) but at the end of the day this was an RA event that occurred between two aircraft in two different traffic patterns that happened to conflict within class east airspace.

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Original NASA ASRS Text

Title: EMB-175 Captain and SAT Approach Controller reported traffic conflict with an unidentified VFR aircraft over 5C1.

Narrative: While flying the BRAUN 2 STAR with an expected visual approach to 13R into SAT; ATC turned our base leg just prior to JATAX. We were given a heading; an altitude of 4;000 feet clearance and ATC pointed out traffic to follow at 10 o'clock; which we called traffic in sight. We were cleared for a visual approach when right at the same moment ATC issued a new traffic advisory for an aircraft they were not in communication with. He started out 1;000 feet below and climbing. We got a TA; and I stated to my First Officer whom was pilot flying to be prepared for an RA as it was not looking very promising.ATC gave us instructions to do whatever we needed to do to avoid the traffic; which we did not have in sight at the time. Just as ATC gave us this command; the TA turned into a descend RA. We initiated a descent. This aircraft was apparently on departure out of a nearby satellite airport and was climbing out. We got two descend RA aural alerts when the collision avoidance switched to a CLIMB; CLIMB NOW aural alert. We immediately changed course and complied with the new RA instructions. We had a jump seater who was commuting home and was familiar with the area. He later stated he did have the traffic in sight during the RA and it appeared to be less than a mile in a 45-degree bank turning away in a climb. Once the RA was resolved; we were in a position to still make a safe landing at SAT and continued the approach. ATC stated they have had numerous issues with aircraft departing out of this satellite airport and have filed numerous reports but nothing has changed.The cause appears to be conflicting traffic patterns between 5C1 airport and SAT. Looking at the airspace charts; the King Air was technically within class E airspace as were we. We may have been just right on the outside ring of the Class C. With a light payload the King Air must have been climbing at a highly unusual rate or maybe a missed go-around from a previous landing attempt but either way proved to be a conflict with our base turn which had us just on the inside of HASDO. As frustrating as the situation was within the current definitions of airspace around SAT it appears there was no airspace incursions and was just a chance encounter. It appears to be a standard issues with aircraft departing out of 5C1.Suggestions: Outside of redefining airspace in the local area; this exact situation will likely continue to happen. With two aircraft in high workload phases of flight; this could definitely cause a major issue in the future. Maybe changing the traffic pattern direction out of 5C1 to a right hand pattern would minimize issues. However; I will continue to be more vigilant on approach into SAT when we are forced to extend our downwind outside of the Class C and I would hope that departing VFR traffic out of 5C1 may elect to get flight following prior to departure (if local ATC offers it) but at the end of the day this was an RA event that occurred between two aircraft in two different traffic patterns that happened to conflict within Class E airspace.

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.