CLARENCE, N.Y. -- Investigators have gathered many of the clues they will need to help decipher why Flight 3407 plunged violently to the earth in icy weather, and they hope to clear the crash site of debris and remains in the next two days.
Some investigators were to leave the site near Buffalo on Tuesday, followed closely by the plane's engine, propeller blades, deicing valves, control yoke and other parts.
Investigators also were analyzing data and voice recorders salvaged from the wreckage and surveying pilots who flew into the area just before or after the Continental Connection flight crashed Thursday.
National Transportation Safety Board member Steve Chealander said investigators already have collected about half the crash debris and want to finish by Wednesday, when a snowstorm is expected to hit the area and hamper the cleanup.
After a seemingly routine flight, the Dash 8 Q400 turboprop plane, operated by Colgan Air, endured a 26-second plunge before smashing into a house about six miles from Buffalo Niagara International Airport. The crash killed all 49 people on the plane and one on the ground.
Though ice has emerged as a possible contributor to the crash, Chealander has not ruled out other possibilities, including other aerodynamic or weight issues that could have made the aircraft uncontrollable.
The crash occurred so quickly and so violently - pitching and rolling the plane almost onto its back at one point and making it plunge 800 feet in just five seconds - that the pilot didn't have time to radio for help. So far, investigators have not found any mechanical problems with the aircraft, and they already have ruled out some causes of previous crashes, such as the loss of a propeller blade.
However, Chealander said investigators will research previous accidents and look for similarities.
On Monday, victims' relatives visited the crash site for the first time and placed red roses on a makeshift fence surrounding it and on the ground.
The site of the house on a quiet, tree-lined street in a middle-class neighborhood is now an almost empty dirt lot. All that is left are a garage with a scorched door, a basketball hoop, four steps leading to nowhere, a mailbox and the plane's enormous tail.
The two closest homes, each no more than two feet from the lot, appear almost untouched.
A tractor lifted the engine's burnt frame, pieces of dirt and charred metal hanging from it, from the lot Monday and put it aside to be investigated. Experts who helped identify victims from Flight 93's crash in a Pennsylvania field on Sept. 11, 2001, joined the search for remains.
Meanwhile, state police closed a road into the neighborhood after residents complained that gawkers were parking cars and trespassing through backyards to get close to the wreckage.
Before Flight 3407 left Newark, N.J., the crew was informed that there was high turbulence in the Buffalo area and possible icing conditions. They turned on the plane's deicing system 11 minutes after taking off, a move Chealander called "very conservative."
Shortly before the crash, at an altitude of between 6,000 feet and 4,000 feet, crew members told air traffic controllers they were experiencing significant ice buildup.
The real trouble began a few minutes later, when the plane descended to just under 2,000 feet, and the pilot lowered the flaps to begin his landing. At that point, the pilots received a signal that the plane was dangerously close to a stall, an aerodynamic condition that causes the plane to pitch forward wildly.
Seconds later, an automatic device called a "stick pusher" pushed the nose down to try to compensate for the problem. The plane then lurched up and back down, rolling violently from side to side as it fell.
Chealander acknowledged that it was possible the pilot overreacted to the "stick pusher" by yanking the yoke back, further destabilizing the plane, but he said that was only one of an almost unlimited number of possibilities.
Kirk Koenig, president of Expert Aviation Consulting of Indianapolis and a commercial aviation pilot for 25 years, said the airplane may have been in a predicament that would challenge even the most experienced pilots.
For example, if ice were forming on the wings, the pilot would want to put the plane's nose down and increase power; if the ice were on the tail, the opposite would have been required - pulling the nose up and reducing power.
"Things happened so quickly, and they were so low to the ground, that it would not have mattered if Chuck Yeager and Neil Armstrong were flying the plane; there wouldn't have been a different outcome," Koenig said.
The plane's deicing system was apparently working, the NTSB has said. Chealander also said a preliminary analysis of the engines was "consistent with high-powered flight," a sign they were operating properly at the time of the crash.
The captain, Marvin Renslow, 47, of Tampa, Fla., was believed to be handling the pilot's duties during the flight's final moments. He had 3,379 hours of flying experience but had flown that type of plane only since December.
The flight's first officer, Rebecca Lynne Shaw, 24, of Seattle, had 2,244 hours of experience and had flown the Dash 8 for 774 hours.
Chealander said investigators would research Renslow's and Shaw's histories, including what they did for 72 hours before the flight.
Associated Press writers Joan Lowy and Pete Yost in Washington, William Kates in Clarence and Carolyn Thompson and John Curran in Buffalo contributed to this report.