Date: 201412
Local time of day: 0601-1200
Location: DEN.Airport, CO
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B DEN
ATC / advisory: TRACON D01
Aircraft component: Autoflight System
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Human factors: Communication Breakdown; Confusion; Distraction; Human-Machine Interface; Time Pressure; Workload
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Automation Aircraft TA; Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC Overrode Automation; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Airport; ATC Equipment / Nav Facility / Buildings; Procedure
Primary problem: Procedure

Narrative: Descending via ANCHR3 Arrival into DEN expecting Runway 35R.  Several approach clearance changes inbound (runway changed from 16 to 35) changed to ANCHR Arrival.  We reprogrammed the FMC and set up for the ANCHR3 followed by visual approach to 35R backed up by the ILS. Approaching DOGGG; we were cleared for the RNAV RNPZ approach to 35R.  We quickly pulled up the new approach on our EFB and I intended to enter the 35R RNP Z approach into the FMC but inadvertently selected the 34R RNP Z approach without realizing it.  I quickly briefed the points while selecting .3RNP; but we were VMC with the field in sight; being instructed to slow to 170 knots getting traffic point outs and configuring with gear and flaps to slow down.  The first two points are the same for both approaches (DOGGG and MSIMS) before the 34R approach continues W across the 35L approach corridor to a final on 34R.  We didn't catch the error and continued to configure.  As we approached the centerline for 35R; it didn't appear that the plane was turning so I disengaged the autopilot and took over visually to not overshoot continuing to a normal landing.  In retrospect; I believe the end game visual approach closely tracked both vertical and lateral course of the RNP approach.  However; there was traffic on final to 35L and if we had not noticed the error and intervened; we could have easily caused a conflict


Second narrative: Approaching the Runway 35R centerline on the base leg; the First Officer (Pilot Flying) realized that automation was not turning us toward the runway. He disconnected the autopilot and made the turn so as not to overshoot. We received a 'Traffic TA' Alert and saw that the traffic for 35L was 300 feet lower. I realized at that point that the FMC must have been programmed incorrectly and quickly reprogrammed RNAV [RNP] Z Runway35R. The remainder of the approach was flown manually and uneventfully.


Synopsis: An air carrier crew entered the FMS ANCHR3 arrival and to expect Runway 35R RNAV RNPZ but mistakenly entered Runway 34R. After a TA alert; they flew the remainder of the 35R approach visually and landed uneventfully.