Investigators began gathering pieces of the incinerated wreckage of a commuter airliner early Saturday in search of clues to the cause of the fiery crash that killed 50 people.
Workers also had begun the somber task of removing the remains of the victims.
Recovering the remains could take several days, said Steve Chealander, spokesman for the National Transportation Safety Board. "We're very sensitive to the families," he said.
Investigators have been examining instrument data and have listened to the last words of the pilot and co-pilot of Flight 3407 in an effort to determine if ice on the plane's wings caused the crash.
Officials say the crew of the Continental Connection flight remarked upon significant ice buildup on the wings and windshield shortly before the aircraft pitched violently and slammed into a house Thursday night.
Ice on the wings can interfere catastrophically with an aircraft's handling and has been blamed for a number of major air disasters over the years, but officials said they had drawn no conclusions as to the cause of this crash.
Chealander said early Saturday that the icing noted by the pilot of Flight 3407 is just one of several things investigators are looking at.
He said the NTSB has been pressing for more regulations to improve deicing.
"We don't like the progress that's taken place right now," Chealander said. "It's something that requires constant focus."
He said the NTSB had made recommendations "for several years."
The aircraft, bound to Buffalo from Newark, New Jersey, went down in light snow and mist — ideal icing conditions — about six miles short of the airport, plunging nose-first through the roof of a house in the suburb of Clarence.
All 44 passengers, four crew members, an off-duty pilot and one person on the ground were killed. Two others escaped from the home, which was engulfed in a fireball that burned for hours, making it too hot to begin removing the bodies until around nightfall Friday.
Investigators pulled the "black box" flight recorders from the incinerated wreckage, sent them to Washington and immediately began analyzing the data.
It was the first deadly crash of a commercial airliner in the U.S. in 2 1/2 years.
One of the survivors from the house, Karen Wielinski, 57, told WBEN-AM that she was watching TV in the family room when she heard a noise. She said her daughter, 22-year-old Jill, who also survived, was watching TV in another part of the house.
"Planes do go over our house, but this one just sounded really different, louder, and I thought to myself, `If that's a plane, it's going to hit something,"' she told the station. "The next thing I knew the ceiling was on me."
She said she hadn't been told the fate of her husband, Doug. "He was a good person, loved his family," she said.
Among the passengers killed was a woman, Beverly Eckert, whose husband died in the World Trade Center attacks of Sept. 11. Last week, Eckert was at the White House with President Barack Obama as part of a meeting with relatives of those killed in the 2001 attacks and the bombing of the USS Cole to discuss how the new administration would handle terrorism suspects.
A Facebook page was dedicated to the victims and their loved ones.
Chealander said Friday that the crew of the twin-engine turboprop discussed "significant ice buildup" on the windshield and the leading edge of the wings at an altitude of around 11,000 feet as the plane was descending for a landing.
The flight data recorder indicated the plane's de-icing equipment was in the "on" position, but Chealander would not say whether the equipment was functioning.
The landing gear was lowered one minute before the end of the flight at an altitude of more than 2,000 feet, and 20 seconds later the wing flaps were set to slow the plane down, after which the aircraft went through "severe pitch and roll," Chealander said.
The crew raised the landing gear at the last moment, just before the recording ran out. No mayday call came from the pilot.
"Icing, if a significant buildup, is an aerodynamic impediment, if you will," Chealander said. "Airplanes are built with wings that are shaped a certain way. If you have too much ice, the shape of the wing can change requiring different airspeeds."
But he refused to draw any conclusions from the data, and cautioned: "We are not ruling anything in or anything out at this time."
Witnesses heard the plane sputtering before it plunged through the roof of the house.
"It was like you were on the runway. It wasn't just different. It was like it was going to hit your house," said Michelle Winer, 46, who ran to look out her front window to see what was happening. "I saw a glow in the sky and I ran to get my husband. He thought I was crazy and then there was a huge explosion. You heard it and felt it."
William Voss, a former official of the Federal Aviation Administration and current president of the Flight Safety Foundation, a nonprofit advocacy group, said the plane's near vertical drop suggests that ice or a mechanical failure, such as wing flaps deploying asymmetrically or the two engines putting out different thrust, caused the crash.
After the crash, at least two pilots were heard on air traffic control circuits saying they had been picking up ice on their wings.
The 74-seat Q400 Bombardier aircraft, in the Dash 8 family of planes, was operated by Colgan Air, based in Manassas, Virginia. Colgan's parent company, Pinnacle Airlines of Memphis, Tennessee, said the plane was new and had a clean safety record.
The pilot, Capt. Marvin Renslow, had been with the airline for nearly 3 1/2 years and had more than 3,000 hours of flying experience with Colgan, which is nearly the maximum a pilot can fly over that period of time under government regulations.
It was the first fatal crash of a commercial airliner in the United States since Aug. 27, 2006, when 49 people were killed when a Comair airliner mistakenly took off from a Lexington, Kentucky, runway that was too short.
In general, smaller planes like the Dash 8, which uses a system of pneumatic de-icing boots, are more susceptible to ice buildup than larger commuter planes that use a heating system to warm the wings. The boots, a rubber membrane stretched over the surface, are filled with compressed air to crack any ice that builds up.
A similar turboprop jet crash 15 years ago in Indiana was caused by ice, and after that the NTSB recommended more aggressively using pneumatic de-icing boots. But the FAA has not adopted the recommendation. It remains on the NTSB's list of most-wanted safety improvements.