Initial National Transportation Safety Board analysis of the flight-data recorder on the crashed Colgan Air Bombardier Q400 shows that the twin-turboprop experienced "severe" pitch and roll excursions after the crew selected 15° flap in preparation for landing.
There were no survivors from the accident which occurred on 12 February as the aircraft was on approach to Buffalo Niagara International Airport.
The pitch and roll upset occurred 20 seconds after the crew had dropped the landing gear, an action that generally occurs at the final approach fix. For Buffalo's runway 23, this fix is 4.4nm from the runway end at an altitude of 2,300ft.
Cockpit voice recorder information from the final 30min of flight reveal that the pilots were discussing a "significant" ice build-up on the windshield and wings, the NTSB says.
Prior to making that comment, the flight data recorder showed that the pilots had placed the airframe de-icing system, which is composed of pneumatic boots on the leading edges, in the 'on' position.
Shortly after the upset, the pilots attempted to raise the gear and flaps, just before the end of the recording, officials say.
The NTSB has updated the fatality count to 50, comprising 44 passengers, one off-duty pilot riding in the jump seat, and four crew members. There was one fatality on the ground.