B737 Undifferentiated or Other Model
Air Traffic Control Fully Certified
Communication Breakdown; Distraction; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action
Human Factors; Procedure
Aircraft X was switched to me outside of the outer marker on a straight in instrument approach for 35L due to us being in a TRIPPS [three simultaneous runways] North Configuration due to the weather. The TRACON had monitors in place so they had control of all of the aircraft up until a mile final to the runway. Even though they were on my frequency final monitor had override capability to give instructions to aircraft. I saw that Aircraft Y was on base executing an RNAV Approach to 34R. Because this is a hot spot situation where aircraft are often pointed at each other before turning final I was paying attention to it. I witnessed Aircraft Y fly past the 34R final and point directly at the path of my Aircraft X with only a couple hundred feet difference in altitude. I immediately issued traffic because I did not have control of the aircraft in this airspace. Aircraft X's pilot came back and advised that he was executing a RA maneuver. Only after this did the Final Monitor key in; issue a traffic alert; and tell the Aircraft X's pilot to climb (which he had already advised he was doing). At the time I issued the traffic advisory the Aircraft Y target was about 20% past 34R in reference to 35L. This is a tough one because it happens more often than it should in IFR and VFR conditions and nothing really seems to come of it. I believe that the controllers at the TRACON should be trying to not point aircraft directly at each other whenever possible in these conditions. Also the Final Monitor is in there for one job; to watch that one final. I don't know what else they are doing but I don't believe that I should be seeing it before they see it.
Denver Tower Controller reported a loss of separation between two aircraft on final while running three simultaneous runway configuration.