Date: 201905
Location: DEN.Airport, CO
Weather elements / visibility: Turbulence
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B DEN
ATC / advisory: TRACON D01
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Confusion; Communication Breakdown; Situational Awareness
Second reporter function: Pilot Flying; First Officer
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: We were given the TELLR 2 RNAV Runway 34R ILS transition. DEN had just changed from south to north flow; we received a new clearance for the TELLR Runway 34 while still at cruise. Once talking to Approach; the controller was very busy. The arrival had a 40 to 30-knot tailwind all the way down. Approximately 10 miles from CRAGG we were vectored off the arrival and told to maintain 210 knots. We were then on a shorter ground track; asked to slow and had a 40-knot tailwind. We used all available drag devices to slow and descend but were still high. We leveled at 13;000'; assigned; and due to communication congestion; we were not able to descend on schedule. All of these made us high on final. We asked for turns on final to try to correct; but were unable to correct. I recollect that Approach asked 'Do you want to try again?' We understood that to mean go missed approach; and agreed with ATC. This began the 'threats' section of this ASAP. The non-standard radio call of 'Do you want to try again'. Followed by 'Turn right 020' left me confused on altitude assignment. We were in a visual descent towards the runway at 9200' (approximately). The altitude bug was at 10;000'; and no perceived altitude assignment. So we climbed to 10;000' while in an assigned left turn to a heading of 170. I did this because 10;000' was the last ATC clearance and was a good safe altitude in that area. With the controller being so busy; I took appropriate action and wanted to ensure aircraft control and; therefore what I perceived as the safest course of action. The First Officer and I were not clear on if we were assigned 9000' or 10;000'. I chose 10;000' due to the altitude bug set there in our AC. I had to make a quick decision and felt 10;000' was the safest; I cleared our flight path and we climbed. I do not believe we were assigned any altitude on missed but we wanted to file to make sure we explained ourselves. Preventative Measures: This is tough; DEN had just changed runways; there was severe turbulence on the arrival; and the tailwind on final. When we landed it seemed that DEN realized the situation and was already changing back to south flow. When I saw the tailwind and the short vector; I used the risk mitigation mindset to help prepare for the possibility of going around. I can understand how busy the Approach Controller was and he did an excellent job! But in the maintain aircraft control; risk mitigation mindsets; I wanted to be able to help him out by making sure we didn't put ourselves in an unsafe situation. So with runway change; turbulence; weather; tailwind; etc.; I don't have a suggestion; this is just aviation. The only thing I would mention is the 737 is very hard to descend and slow; even harder with a tailwind and turbulence. A longer ground track (not shorter) is the best way to go during these scenarios. On missed approach keep standard communication '(Call sign) execute a missed approach; heading XX climb maintain XX altitude.' Let us respond; then 'expect vectors to ILS Runway 34R.' This scenario had three turns in less than 30 seconds; with some hesitation that caused CRM to break down.


Second narrative: I was PF (Piot Flying) initially. We were given an arrival change to Denver that had us flying the TELLR Arrival; initially we were coming in more from the northwest avoiding the weather as filed by Dispatch. Anyways; we avoided the weather on the TELLR but bounced around quite a bit after Denver made us descend early as well. However as we got closer to the airport they switched descending us early and held us at 13;000' at 250 knots. Approaching another cell close to BOOBO on the final for 34R we asked for a turn. They gave us straight to the final approach fix and a descent to 10;000' at 250 knots. I threw out the speed brakes; realizing we needed to get down; passing about 10;500 he told us to slow and cleared us for the visual. I basically leveled and hung out the gear and flaps after stowing the speed brakes and tried to descend to profile after getting the speed down and dirty. Through 9500'; I told the Captain there was no way to make it work and he asked for S-turns. They approved turns to the west so I clicked off the automation and started an S-turn to the west; then back to centerline; but passing 9000' he agreed that Denver left us too high and we could not get it down stabilized. We told Denver we were going around. Denver told us to maintain 9000' and gave us a 020 degree vector over the field. I hit TO/GA as we descended to about 8800'; as Denver gave us 9000'; I pushed power up and started a very slow climb up to 200' and called for flaps 15 and landing gear up established in my shallow climb. I leveled at 9000'; called for flaps 5 at the bug; and asked for 9000' in the altitude window; since we had just left 10;000' in the altitude window and the command bars were commanding a climb. However; Denver gave us a 050 heading and then I believe a frequency change to Approach; and then they quickly asked for a westbound turn. As I turned west; I overbanked after some turbulence but quickly brought the bank back to 30 degrees. I climbed 100' to 9100' and noticed flaps were still at 15; so I brought a little power back as not to over speed flaps and to get back to 9000'. I think the Captain saw 10;000' still in the window and stated we needed more power; so I added a little back in; which stabilized the speed a little above the flaps 15 bug; which is where I think the Captain; ATC and I all got on different pages. I thought ATC was basically vectoring us a 360; and the Captain wanted the flaps 15 because as soon as we made our quick downwind turn we would need the gear right back down to get down for a quick turn back to final. I was going to hit Altitude Hold; but I thought out of g-around mode I would set off the gear horn. Upon debrief the Captain indicated that he thought we were going to fly a long downwind to be re-sequenced; and we were not sure what ATC was doing. Anyway; since I pulled some power back and the Captain thought we should be climbing; and he thought we were slow; he said that he had the aircraft. He added power we cleaned up the aircraft and he accelerated to 250 knots and climbed to 10;000'. I mentioned twice as he was climbing that we were only cleared to 9000'; but he said no 10;000'. ATC immediately re-cleared us to 9000' when we got to 10;000' and then 7000' to bring us just outside the FAF for 34R. We scrambled again to get down and stabilized; but were able to stabilize with a descent rate under 1000 fpm and land. The Controllers never questioned that we climbed to 10;000'; but debriefing; I stated that I must have missed our clearance to 10;000' and the Captain stated that in hindsight he did not remember ATC clearing us to 10;000'. Preventative Measures: I think I called for it twice; but I should have just moved the flaps to 5. I think the Captain thought we did; but I know the PM can get jammed up with a lot of stuff to do especially when tied up with repeated ATC instructions. This would have left us in a good position for me to hit Altitude Hold; put on the autopilot; dial in 9000';fly at 190 to 210 knots; and turn on the autothrottles; which would have been a good speed to start with to determine if we were coming right back or if it would have been a little while to be re-sequenced. Then we could have also taken a moment to most importantly all get on the same page.


Synopsis: B737 flight crew reported confusion over their assigned altitude on a go-around from an unstabilized approach to DEN.