Air carrier flight crew reported receiving a low altitude alert from ATC during descent in IMC weather conditions. Flight climbed and continued approach.
Synopsis
Air carrier flight crew reported receiving a low altitude alert from ATC during descent in IMC weather conditions. Flight climbed and continued approach.
Narrative
I was the PM; and the FO was the PF. We were in IMC and were expecting the RNAV approach to Runway 13 at Bismarck (BIS).During descent; Approach Control vectored us northwest and cleared us to descend to 3;700 feet. The FO briefed that he would descend then slow the aircraft which I agreed with since it would give me time to input ice speeds if they were encountered.Upon reaching 3;700 feet; ATC issued a low altitude alert and instructed us to climb immediately to 5;000 feet. At the same moment; the aircraft's Enhanced Ground Proximity Warning System (EGPWS) announced 'Caution; Obstacle.'We initiated an immediate climb to 5;000 feet. ATC then vectored us onto the RNAV approach to Runway 13; and we executed a normal landing. Cause: While complying with our ATC clearance we descended quicker than anticipated due to the strong headwinds. After the event we both verified our altimeters were set to the correct setting per the ATIS. The highest obstacle on the approach plate was 3081' and the highest obstacle we observed in our approach path was 2337'. Just outside the approach plate the VFR sectional indicates an obstacle at 3393' to the south west of the airport. Suggestions: Descending via path would have brought us to our target altitude closer the approach end of the runway. Better descent planning.
Second reporter narrative
I was pilot flying. The captain was pilot monitoring we were given a clearance to descend from 7000 feet to 3700 feet. We were originally thinking we would have ice speeds and so I planned to go ahead and descend about 20 miles south of the airport. upon reaching the altitude of 3700 feet ATC immediately issued new instructions to start a climb to 5000 feet. Upon initiating the climb; the Enhanced Ground Proximity Warning System (EGPWS) issued a caution message saying obstacle. After climbing and reaching 5000 feet; we were then issued clearance to descend for the approach and landed without further complications.Cause: Unclear ATC instruction for approach without possible obstacle consideration for an early decent for possible ice speeds in IMC conditions.Suggestions: Better altitude planning in cold temperatures and IMC conditions. And better communication with ATC.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.