Date: 201710
Local time of day: 1801-2400
Location: DEN.Airport, CO
Flight conditions: VMC
Light: Daylight
Aircraft: B737-900
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach; Final Approach
Airspace: Class B DEN
ATC / advisory: TRACON D01
Second aircraft: B737-700
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Communication Breakdown; Workload; Confusion
Second reporter function: Captain; Pilot Flying
Anomaly: Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: Aircraft X checked in; and was cleared for RNAV Zulu Runway 35R approach. Pilot read back approach clearance correctly I slowed aircraft to 190 KTS to keep separation as Aircraft X was in trail of two other aircraft on [RNP] approaches. Winds were strong out of the south at altitude and needed to control speeds on the downwind and base legs of the approaches. It appeared Aircraft X was turned in to join the final and so I instructed Aircraft X to contact tower on 133.3. The pilot replied with 'Verify Runway 35R' at which point I stated 'Yes; Runway 35R and recognized that the aircraft was heading due west bound and not turning onto the final. The controller next to me (working Flight Radar 1) had two aircraft and it appeared that Aircraft X was now going to conflict with both of those aircraft; so he issued traffic and was able to get Aircraft X in sight. I then reached out to Aircraft X and instructed the pilot to turn due northbound to try and avoid a conflict with the aircraft on Runway 34R. The Flight Radar 1 controller issued traffic again and once Aircraft X was in the turn - I instructed him to climb to get out of the way. Then re-vectored pilot for visual approach to Runway 35R.Aircraft Y- aircraft that was on final for Runway 35L was issued traffic and saw Aircraft X. Due to aircraft's TCAS; pilot had to initiate a rapid descent which contributed to the aircraft being much lower than Aircraft X. If pilot is confused; they need to clarify which runway well before the position the aircraft was in. I observed Aircraft X on a heading turning in; when in reality they turned more westerly after questioning which runway they were going to. Not sure why a pilot would think they were going to cross over 2 different finals to go to a runway on the west side of the airport...; which appeared to be what they were doing.Procedural: We have maps that show the exact RNAV path that each aircraft is supposed to be flying depending on which runway they are going to - there are SLIGHT variations with the turns to join the finals depending on which runway is assigned - and had I been working with this map displayed (although this is not a requirement) I would definitely have noticed that Aircraft X was not turning in to the correct runway. I will be working with this map displayed on my scope from now on. This should probably become a requirement for all controllers.


Second narrative: We were cleared for a straight-in Visual Approach to Runway 35L at DEN. We were lined up with the runway approximately eight miles out. After selecting gear down and flaps to 15; my First Officer sighted traffic at our 1 o'clock position on a heading of approximately 270 degrees; which was 90 degrees perpendicular to our heading. He said; 'Wow they are being aggressive.' Shortly thereafter; it became apparent they were not lining up with their assigned Runway 35R. They were clearly going to infringe on our airspace on the 35L final. As this was occurring; the TCAS generated a very aggressive descend RA to avoid colliding with the (other carrier) Aircraft. We had no choice but to assertively follow the Descend RA to avoid a collision. The maneuver was felt by our Flight Attendants and Passengers. The (other carrier) aircraft continued on a westerly heading and conflicted with another 737 that was lining up for 34R. We later learned that the (other carrier) 737 Crew had mistakenly entered 34R into their FMC for the Require Navigation Performance Approach instead of 35R which was the approach and runway they were assigned.


Synopsis: Denver Approach Controller and four pilots reported that an aircraft went through assigned final course causing an airborne conflict with two other aircrafts.