B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 240; Flight Crew Total 4300; Flight Crew Type 4050
Situational Awareness
ATC Issue All Types; Conflict NMAC
Flight Crew Took Evasive Action
Human Factors; Procedure
We were cleared LEMIG 1 arrival; after ELKAY fix we were assigned heading 330 as vector to rwy 12R; we were instructed to maintain 6;000 ft; by about 9 miles away from ISAT LOC; ATC told us to descend to 3;000ft; turn right heading approximately direct ALAMO fix (don't remember exact heading) and to look for traffic at 12 o'clock; that [we were] number 1 for approach to 12R; we answered that we were looking for traffic and started turning and descending to 3;000 as instructed. 30 seconds later ATC told us that traffic was now at 2 o'clock; this time we saw it and told ATC. Then we were cleared to visual approach 12R and instructed to maintain visual separation with traffic. And so we did. By then; the traffic ahead was approximately 4 miles from us so FO decided to reduce speed by configuring aircraft for landing; and maintaining present heading a while longer in order to follow traffic with safe separation. I realized that we were now at a good point to turn to final and told FO to start turning right; When we were turning final; intercepting localizer; at about 2;800 ft and 7 miles final a TA advisory was heard; so I started looking for traffic; it appeared in my EHSI a traffic at left but I couldn't get a visual of the aircraft; while this; our aircraft was in a continuous right turn to intercept final and descending to intercept glide path; just about 6 seconds after the first TA; a RA started instructing us to CLIMB and in our EADIs a pitch of almost 20 degrees nose up was required; FO correctly leveled wings; applied pitch up and maximum thrust; the aircraft climbed slowly so we decided to rise the gear and set flaps to 15. After the RA escape maneuver; 'Clear of conflict!' was heard and advised ATC about the situation; then they gave us left vectors to re-intercept final approach. When all was under normal conditions and control; I requested ATC to inform us about the traffic that got in conflict with us; and only told us that was a visual traffic that had us in sight. At the moment of climb I think I saw about 100ft of vertical separation with traffic! So it really was a close call. At no moment during the approach were we informed about this third traffic; if he was supposed to maintain visual separation with us; he clearly didn't do it. ATC had cleared us to a visual approach; so we were responsible [for] altitude and traffic separation with the traffic ahead; but this other small VFR traffic was never in our situational awareness; nor in our EHSI but until very late to avoid. And why was this traffic flying at that altitude at that point of the final approach path of the runway; without any ATC warning to us?
B737 Captain reported an NMAC with another aircraft on approach to SAT that was not pointed out by ATC.