Flight crew reported they were descending to their ATC assigned altitude when they received a Terrain Warning.
Synopsis
Flight crew reported they were descending to their ATC assigned altitude when they received a Terrain Warning.
Narrative
During the final descend to ZZZ we contacted ZZZ Approach and received instructions to descend 3000 ft. and expect vectors for ILS X at ZZZ airport. We descended through 4000 ft. to 3000 ft. with vertical speed 1000 fpm and received next instruction to descend to 2000 ft. I've read back this instructions with no ATC challenge and set 2000 ft. on altitude preselector. Pilot flying (PF) verbalize new altitude and we continued descend to 2000 ft. as instructed by ATC. We were in IMC conditions and experienced light turbulence also according SOPs pilot flying MFD was on terrain mode (for terrain airport) and my MFD was on Weather mode with radar on (due to Weather activity along the route). Terrain depiction on PF MFD was normal and did not lead us to query ATC instructions.When we crossed approximately 2500 ft. aural warning 'PULL UP TERRAIN' went off and second later we executed terrain escape maneuver. Few second later during climb approximately at 3500 ft. ATC querying as about altitude and notified us what last assigned altitude was 3000 ft. I notified ATC what we executed terrain escape maneuver and we will climb to 5000 ft. We leveled off at 5000 ft. After level off I notified ATC and explain what happened. ATC query us about our intentions and after quick brief we decided to continue as planned to destination. Rest of the flight went uneventful. We didn't receive instructions to call ATC by phone. We debriefed this situation on the ground upon completion of the flight. During debrief we both agreed that ATC gave us instructions to descend to 2000 ft. but we should query this instructions because FAF altitude is 2600 ft. Both of us have never been at ZZZ and we were unfamiliar with common ATC procedures at this airport. Pilot Flying during approach briefing mentioned notes on 10-7 page for visual approach for Runway X but we did ILS approach and follow ATC instruction. We should query any ATC instructions if in doubt.
Second reporter narrative
Late night on approach into ZZZ ILS X approach was briefed and told to be expected by ATC as the slightly gusty winds were right down the runway and the ceiling was somewhat low around 2000 ft. As I briefed the approach; I noted that it was a terrain airport due to terrain out west and I also noted the ridge that was around 1804 ft. and featured on the company notes page for ZZZ. This was primarily a caution for people executing a visual approach into Runway X not an ILS approach. Beginning the descent from 8000 to 3000 as instructed by ATC; ATC told us to expect vectors for the X ILS as briefed. As we closed in on leveling off at 3000 ft. (about 4-5 miles east south-east on downwind) we hear another instruction from approach control to descend and maintain 2000 ft. Pilot monitoring (PM) read back altitude with no challenge from ATC. 2000 was set in the altitude window and we began a descent (around 1000-1200 fpm). Within a very short window of time after this; with no other present warnings or cautions we got a GPWS 'GND PROX'; and 'Pull up'. With minimal delay I executed an escape maneuver and climbed to 5000 which was well clear of the terrain displayed on the MFD terrain display function. After recovering we queried ATC about the altitude they had assigned; ATC said it was 3000 and said we were coming in broken and unreadable. After the event we received vectors for the ILS X and then proceeded and landed without incident. Next time I will more than triple check the altitude that ATC has us to descending to intercept the course and glideslope. ATC made a clear error in issuing this clearance; and then after the fact said 'no I said to descend and maintain 3000'. I'm sure late night fatigue was at play; when people are saying one thing but meaning another. Whatever the case better work all around was due to help avoid a scenario like this. I should have caught right when the instruction was given that the glideslope intercept altitude was 2600 ft. on the approach not 2000 ft. It's a great idea to pay close attention to the lay of the land; even if it's only a dot or simple feature on our approach plates it's there for a reason. The terrain feature I suspect that must have triggered the terrain closure warning would have been the ridge that is mentioned to be at 1800 ft. on the airport 10-7. In our debrief we noticed on the plate the only significant terrain illustrated on the plate is out to the west; while the 1800 ft. peak is denoted only by a dot.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.