Date: 201810
Local time of day: 0601-1200
Location: DEN.Airport, CO
Light: Dawn
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B D01
ATC / advisory: TRACON D01
Second aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Workload
Second reporter function: Pilot Flying; First Officer
Anomaly: Conflict Airborne Conflict; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach
Detector: Automation Aircraft RA
When detected: In-flight
Result: Flight Crew Executed Go Around / Missed Approach
Contributing factors: Airport; Human Factors; Procedure
Primary problem: Ambiguous

Narrative: Coming into DEN 16L for the visual on an extremely busy morning; we were cleared for the visual to 16L behind [another aircraft]; three to five miles ahead of us and were told to hold 160 KIAS to the FAF. On approximately 12-mile final; we heard ATC call out traffic behind us converging towards the parallel 16R. Shortly after; we received our first RA. The First Officer (FO) reacted appropriately and we were quickly Clear of Conflict. We informed Approach and let them know we were continuing. Again; at around a seven or eight mile final; we received an RA to descend. Following the RA we got fast (approximately 190 KIAS). We also descended to approximately 7600 feet before the RA went away. At that point we began a very shallow non-standard go-around because we were partially configured; closing on the traffic in front of us; and concerned much of a climb would put us into conflict with the traffic behind us again. Frankly; we were threading a needle because ATC had high radio congestion; there was traffic in front of us; traffic to our right; and traffic on approach to our left. While reacting the second time; we informed ATC and let them know we would be going around. ATC gave us a warning that we were too low; and switched us to Tower for go-around instructions. Once on Tower we began transitioning to a normal go-around and returned to land uneventfully.


Second narrative: As we approached from the east; heading west; we were cleared for Visual Approach to 16L. Our interval was [another aircraft] which we had sight of. While turning left onto final we got a TA from traffic behind and above us. I looked outside the right aft window and saw the traffic which was heading east (flying perpendicular to our flight path; and it appeared to be passing behind us (tracking aft of us visually). As I rolled out on final; the TA went away. ATC had not mentioned anything about the traffic behind us. Once established on final course; we were instructed no slower than 160 knots to FAF. I rolled MCP speed to 160 and began slowing from 180. We then got an RA displaying double red line box above the horizon and 'descend' aural warning. I disengaged autopilot and auto throttles and positioned the nose of the aircraft below the red box; approximately on the artificial horizon. The RA went away and I leveled off and continued with the approach manually. The Captain informed ATC of the RA. About 30 seconds later it happens again; and I responded the same. At that point we had descended below glideslope due to RA commands. Once we cleared the RA; we were level around 960 feet AGL. Captain had already called for the go-around so I executed the go-around and started climbing. Go around and subsequent visual approach to landing on 17R was uneventful.


Synopsis: B737 flight crew reported two TCAS RA's while on approach to DEN that resulted in a missed approach.