'Ice build-up' on crashed plane
Press conference on black box findings: "Significant ice build-up"
The crew of a plane that crashed in New York state killing 50 people noticed "significant ice build-up" on its wings before it crashed, investigators say.
Analysis of data recorders recovered from the scene shows the plane made a series of severe pitches and rolls seconds before plunging into a house.
Continental flight 3407 was minutes from Buffalo airport when it crashed at 2210 (0310 GMT) on Thursday.
Officials say the cause of the crash is still under investigation.
National Transportation Safety Board spokesman Steve Chealander said emergency teams were working to recover victims' remains from the site of the crash.
The dead include 44 passengers, four crew and one off-duty pilot on board, and one person on the ground.
Snow and mist
The twin-prop Bombardier Dash 8 Q400 aircraft, operated by Colgan Air for Continental Airlines, was flying from Newark airport in New Jersey to Buffalo Niagara International Airport.
The pilots did not tell air traffic controllers of any problems during the flight, and a recording of communications appears normal until shortly before the crash.
However, Mr Chealander said the aircraft's cockpit voice recorder captured the crew discussing landing the aircraft at Buffalo and noting snow and mist.
At 16,000ft they said conditions were becoming hazy and asked for permission to descend to 12,000ft.
After that they were cleared to descend to 11,000ft.
The crew subsequently discussed "significant ice build-up" on the windshield and leading edge of the aircraft's wings, Mr Chealander said.
The official added that before these comments were made, the plane's de-icing system had been switched on.
'Severe pitches and rolls'
One minute before the end of the recording, the plane's landing gear was put down. Twenty seconds later the crew repositioned the aircraft's wing flaps to slow it for landing.
We kind of keep expecting Becky to come around the corner and say it's not real
Mother of co-pilot Rebecca Shaw
'The plane didn't sound normal'
9/11 widow among dead
In pictures: Buffalo crash
Within seconds of the flaps being moved, the aircraft experienced a "series of severe pitches and rolls", Mr Chealander said.
Just before the recording ended, the crew tried to raise the landing gear and reposition the flaps, he added.
Other pilots had reported ice forming on the wings of their planes.
A minute after one response, the air traffic controller was unable to contact flight 3407 and asked other planes in the area if they could spot it.
One airport official said he had been told "the plane simply dropped off the radar screen".
Eyewitnesses spoke of hearing unusual sounds coming from the plane before it crashed.
BOMBARDIER DASH 8 AIRCRAFT
The Canadian-made Bombardier Dash 8 Q400 was delivered new last year
Q400 is newest member of the Dash 8 family
Twin-engine turboprop, mainly for short-haul flights
First flown in 1998, entered commercial service in 2000
Among those on board was Beverly Eckert, the widow of a victim of the 9/11 attacks and who became a campaigner on security issues.
President Barack Obama said he and his wife Michelle were "deeply saddened" by the news.
He also paid tribute to Ms Eckert, calling her "an inspiration to me and so many others".
Alison Des Forges - a writer and human rights expert on Rwanda - was also among those killed, said New York Governor David Patterson.
Lynn Morris, whose daughter Rebecca Shaw was the co-pilot, said: "It's very difficult, we kind of keep expecting Becky to come around the corner and say it's not real."
"We didn't find out until four-thirty this morning that she was actually on the flight."
Two people - believed to be a woman and child - who were also in the house that was hit are thought to have escaped with minor injuries.
Dave Bissonette, emergency control director in Clarence, said it was "remarkable" that only one house was hit, with neighbouring homes relatively unscathed