Air Carrier Pilots reported there were late runway changes in this mountainous area. Then while executing an RNP approach in a Heavy Aircraft; they received two GPWS Terrain Warnings and conducted a missed approach. There was a tailwind on the RF leg and each pilot stated they think the terrain warning was caused by the excessive speed from the tailwind. The airport was turned around after their missed approach.
Synopsis
Air Carrier Pilots reported there were late runway changes in this mountainous area. Then while executing an RNP approach in a Heavy Aircraft; they received two GPWS Terrain Warnings and conducted a missed approach. There was a tailwind on the RF leg and each pilot stated they think the terrain warning was caused by the excessive speed from the tailwind. The airport was turned around after their missed approach.
Narrative
Flight plan release filed ILS ZZZZZ1 for Runway XXR. ATIS at cruise was calling for Runways YYL/R. Loaded and briefed ILS ZZZZZ2 for YYL. ATC clearance passing ZZZ1: pilot's discretion to FL250 ILS ZZZZZ2 for Runway YY. Prior to ZZZZZ3 we were given a heading of 160 for 2 minutes then back to ZZZZZ3. Next ATC clearance was direct ZZZZZ4 descend to 18000. Around ZZZZZ4 frequency change. Next controller gave us direct ZZZZZ5 descend 15000.We had briefed/anticipated this possibility. We requested RNP ZZZZZ6. At this time; there was confusion with ATC with which runway we were going to get assigned. Holding instructions were being given to other aircraft. We briefly talked about the possibility of holding at ZZZZZ5. Airport was in the process of switching the Runways to XXL/R. ATC came to us and assigned YYR. Apparently we would be the last ones in before the switch. Quickly loaded the FMS and briefed the approach. We reconfirmed our approach assignment based on all the transmissions to other aircraft being given XXL. Cleared for the RNP ZZZZZ6. After ZZZZZ5 but prior to ZZZZZ7; ATC gave us a clearance to maintain 190 kts. Passing ZZZZZ7; we asked to slow down to meet the restriction at ZZZZZ8. ATC's response was 'you're cleared for the approach'. Aircraft configuration at this time was gear down; flaps 20 slowing to meet the 'at 185 kts.' at ZZZZZ8. Aircraft is in VNAV PATH descending; speed brakes were being used to help slow. The next sequence of events happen very quickly and are in the best order of memory. While waiting for the airspeed to go below the next flap setting; we received a terrain caution from the GPWS. ATC asks if we are 'on track'; 'do you see the runway?' We break out of some clouds and can visually see terrain. In my quick assessment of the aircraft's descent rate and track; it didn't look like we were going to clear the terrain. Pilot Flying selects ALT HOLD to discontinue approach. We receive another terrain caution. With all of these factors and knowing that we were very close to mountainous terrain; a GO-AROUND was performed as there was some doubt that we may not be on track. We maintained the approach ground track while cleaning up the aircraft. ATC provided vectors to the ILS ZZZZZ 9 and landed. ATC [made a] last minute change of runway. Assigning an airspeed to maintain after clearance for the approach was given and not deleting the airspeed assignment. Approach design could be a factor as the 185 kts. restriction at ZZZZZ8 doesn't allow for configuration to happen in this Heavy Aircraft. (180 kts. for flaps 25/30). High TAS with aircraft descending in VNAV PATH makes it difficult to slow. Having loaded Runway YYR approach in the secondary flight plan could have helped with less FMS workload and more monitoring of the approach.
Second reporter narrative
ZZZZ [Airport] had winds from the northwest at around 10 kts.; a 2000 ft. ceiling; and ATIS advertised RNP approaches to runways YYL/R. We built and briefed the ILS ZZZZZ2 arrival and the RNP ZZZZZ6. On the arrival between ZZZZZ3 and ZZZZZ4 we get switched to Approach control- in one transmission the controller tells us to expect the Visual RNP ZZZZZ9; to descend to 15000 ft.; and to proceed directly to ZZZZZ5- the terminus of the arrival and the IAF for the Runway YYL/R RNP procedures. We requested the RNP ZZZZZ10 due to the low ceilings. After a slight delay; the controller told us to expect that. The PM loaded the new approach and gave me a briefing on the differences. On the approach past ZZZZZ5 but prior to ZZZZZ7; the controller assigned us 190 kts.- slower than the required 215 kts. at ZZZZZ7. At this point; I had completed the 'LAVS' procedure and was configured with flaps 15 and speed breaks extended to help reduce speed. Approaching ZZZZZ8; the Pilot Monitoring told the controller we needed to reduce our airspeed. The controller said we were cleared for the approach and to resume published speeds. With the speed window open; I selected 185 kts. (the required speed at ZZZZZ8) and called for landing gear down and flaps 20. Passing ZZZZZ8; I reduced the selected speed to 160 kts. in order to slow for the RF leg and to meet the speed restriction at ZZZZZ11. At this point on the approach; I was at 180 kts. with the flaps at 20; landing gear down; speed breaks extended on LNAV and VNAV PTH. Further; I noticed we had about a 10 kt tailwind. Several seconds into the RF leg we received a GPWS terrain CAUTION alert. The Pilot Monitoring and I decided a go-around was appropriate. As I was taught in training and had previously briefed; I discontinued the RNP approach by pushing the ALT HOLD switch to remain in LNAV. However; momentarily after pushing ALT HOLD we received another terrain CAUTION alert. The Pilot Monitoring and I agreed we needed more altitude; so I simultaneously pressed the go-around switch and disconnected the autopilot. The Pilot Monitoring was communicating with ATC at this point. I used the Navigation Display to keep the flight path aligned with the RF course. Realizing the Pilot Monitoring was still talking to ATC; I pushed the LNAV button on the Mode Control Panel and resumed a normal go-around procedure up to the ATC assigned altitude of 14000 ft. I called for the autopilot once the Pilot Monitoring was done communicating with ATC. We cleaned the airplane up to flaps 5 and; because ZZZ1 was in the process of turning the airport around; received vectors to the ILS ZZZZZ12. The Pilot Monitoring rebuilt the FMS and briefed me on the new approach and I requested the In-Range and Approach checklists. I flew the ILS to XXL and landed with no further incident. I believe the terrain CAUTION alert was caused by a high descent rate on the approach- a product of high airport elevation; a tailwind; and a 185 kt. speed requirement at the beginning of the RF leg. Even though the FMA's showed we were on VNAV PTH; our descent rate was around 2000 fpm when the terrain CAUTION alert happened. Additionally; as well prepared as we were for the arrival and approach; there were numerous unnecessary threats that degraded the level of safety for the operation. First; ATC was the biggest threat. Each runway in ZZZ1 has multiple approaches- not knowing what runway or approach ATC will assign until 10000 AGL is a setup for failure. While the Pilot Monitoring is busy requesting and loading a different approach; it removes them from the control loop of the airplane. Further; ATC requiring other than posted speeds on an RNP approach causes an increase in the Pilot Flying's workload. Second; the actual speed requirements on these ZZZZ RNP approaches are unrealistic for a Heavy Aircraft. If that 185 kt. restriction at ZZZZZ8 didn't exist; I would have been fully configured with flaps 30 and landing gear down with a much slower indicated airspeed. Maybe the terrain caution would not have activated at a slower indicated airspeed/lower rate of descent. Lastly; the weather (marginal VMC and a tailwind on downwind/base) was a threat to safely executing the RNP into YYR. Along the arrival and approach I heard ATC assign airplanes the ILS approach to XXL- I knew they would be turning the airport around after our approach. With the winds shifting to the south; the approach we were assigned wasn't very feasible. It would be helpful if we only had one RNP approach for each runway that we could fly. If the controllers knew we could only ever do the RNP ZZZZZ6; for example; it would eliminate a lot of unnecessary time spent on the radio; heads down; and changing what was already set up and briefed. Further; either the required speeds on the RNP's to YYL/R need to be lowered or there should be a tailwind restriction or a note cautioning pilots to tell ATC they cannot safely make those posted speeds. Additionally; it would be beneficial to include a set-up like this for simulator training. Having to evade terrain while simultaneously fly an RF leg on an RNP is something that I do not recall seeing before in training.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.