Mr Chealander says use of the aircraft's autopilot was normal
A plane that crashed onto a house in New York state, killing 50 people, dropped by 800 feet (245 metres) in five seconds, officials say.
Air safety official Steve Chealander said the plane had fallen from 1,800ft to 1,000ft shortly before impact.
He also said investigators had not found that there were "severe icing" conditions, which would have required pilots to fly the plane manually.
The plane's autopilot was on until just before the crash, Mr Chealander said.
Analysis of the plane's data recorders shows the crew noticed significant ice build-up on its wings before the crash.
Mr Chealander, a spokesman for the National Transportation Safety Board (NTSB), had earlier told the the Associated Press news agency that the NTSB recommended pilots disengage their craft's autopilot facility in icy conditions.
The plane's de-icing system had been switched on before the crash
Pilots using manual controls may be able to sense a problem sooner than the autopilot, he said.
But in a press briefing on Sunday he said there was no evidence that the Continental Airlines pilot had done anything wrong.
"The only restriction that they see - the manufacturer of this airplane - and that they write about is that disengage the autopilot in severe icing conditions," Mr Chealander said.
"Thus far we haven't determined that it's severe icing so, so far we see that everything seemed to be normal in using the autopilot."
Pitches and rolls
The Bombardier Dash 8 was approaching Buffalo's airport when it crashed flat on the house in Clarence Center, a suburb of Buffalo, last Thursday.
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
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