(CBS/AP) The sounds of the last desperate minutes in the cockpit aboard Flight 3407 could be clues to the cause of a crash that came violently and suddenly, with the doomed plane dropping steeply and pitching and rolling like a rollercoaster.
Investigators in Washington and Buffalo have begun an in-depth study of the plane's voice cockpit and voice data recorders.
They also plan to scrutinize all pieces of the engines to learn whether the plane was intact when it hit the ground. Steve Chealander of the National Transportation Safety Board said the engines would be taken by crane from the debris field on Monday.
On The Early Show Monday, Chealander said co-anchor Harry Smith was on-target in asking, "There's not a clear, black-and-white case in terms of what happened Thursday night?"
"To characterize the pilots as having done something wrong is incorrect at this time," Chealander replied to Smith. "We don't want to go there. ... All the procedures that he was supposed to do, thus far, we see were being done."
Families of the victims visited the site Monday. They boarded several buses at the hotel where they are staying and drove to the crash site with police escort.
On Sunday, Chealander released facts illustrating how the Continental Connection flight disappeared from radar late Thursday, plunging into a house and killing 50 people.
Chealander said information from the plane's flight data recorder indicated that the aircraft pitched up at an angle of 31 degrees in its final seconds, then pitched down at 45 degrees.
The plane rolled to the left at 46 degrees, then snapped back to the right at 105 degrees - 15 degrees beyond vertical.
Radar data shows Flight 3407 fell from 1,800 feet above sea level to 1,000 feet in five seconds, he said. Passengers and crew would have experienced G-forces up to twice as strong as on the ground.
Authorities said Monday that gawkers continue to seek access to the site, forcing officials to again close a road that leads to the suburban Clarence neighborhood where the plane crashed into a house, killing all 49 people on board and one person in the home.
A road that leads to the neighborhood was reopened to traffic about 6 p.m. Sunday but closed again after residents complained that people were parking cars and then trespassing on backyards in a bid to get close, according to Capt. Steven Nigrelli of the New York State Police.
Three people have been arrested trying to get to the site, including a man caught hiding behind a home and videotaping the crash site Friday.
The plane crashed belly-first on top of a house about six miles short of Buffalo Niagara International Airport, two to three minutes from when it should have touched down on the runway.
Just before they went down in a suburban neighborhood, the pilots discussed "significant" ice buildup on their wings and windshield. Other aircraft in the area told air traffic controllers they also experienced icing around the same time.
Chealander said in an interview that the pilot may have rejected federal safety recommendations and the airline's own policy for flying in icy conditions by leaving the autopilot on even after he notified air traffic control that the flight crew had spotted ice on the leading edge of the wings and the windshield.
However, reports CBS News' Nancy Cordes, Chealander said Sunday that, at this point -- based on weather reports and accounts from nearby pilots -- there is no indication that the icing conditions in the area that night qualified as “severe,” though information is still being gathered. In non-severe icing conditions, the manufacturer's manual merely recommends disengaging the autopilot.
The pilot himself was heard describing the ice buildup that night as “significant,” which is a colloquial rather than official term, making it difficult to know just how bad the icing was, Cordes reports, adding it’s kind of like saying it’s “pretty” rainy outside - what that means is open to interpretation.
The Dash 8 Q400 plane, operated by Colgan Air, was equipped with a "stick shaker" and "stick pusher" mechanism that rattles the yoke to warn the pilot if the plane is about to lose aerodynamic lift, a condition called a stall. If not corrected in time, the mechanism automatically pushes the stick forward to avert a stall.
Chealander said the plane was on autopilot until the "stick shaker" and "stick pusher" kicked in, automatically putting the plane back in the pilot's hands.
At some point, the pilot switched on an anti-stall device that increases the speed of the plane by 20 knots and gives a pilot more margin to recover from a stall if it occurs.
Asked whether the pilot might have overreacted by pulling the stick back when it automatically went forward, Chealander said, "Yes, it's possible."
Still, he was careful not to be critical of the pilot.
"Everything that should have been done was done, so we keep looking," he said. "We keep looking, trying to find out why this happened."
Chealander said the plane's deicing system was turned on 11 minutes after it took off from Newark, N.J., and stayed on for the entire flight. Indicator lights showed the system appeared to be working.
He said the pilot was being "very conservative" by turning it on so soon.
Investigators who examined both engines said they appeared to be working normally at the time of the crash.
Colgan Air operates a fleet of 51 regional turboprops for Continental Connection, United Express and US Airways Express.
By Sunday, authorities had recovered the remains of 15 people from the wreckage as crews raced to finish their work before a storm expected later in the week.
Recovery crews could need as much as four days to remove the remains from the site. Chealander described the efforts as an "excavation."
"Keep in mind, there's an airplane that fell on top of a house, and they're now intermingled," he said.
DNA and dental records will be used to identify the remains, he said.
Once all the remains are recovered, the focus will turn to removing wreckage of the 74-seat aircraft from the neighborhood.
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