However, reports CBS News' Nancy Cordes, National Transportation Safety Board member Steven 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.
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."
Chealander also said Sunday that the de-icing equipment was turned on 11 minutes into the flight -- well before the plane would have encountered the icy conditions near Buffalo. And he said there is no evidence that the autopilot went through a series of "trims" trying to compensate for significant ice buildup before the plane lost control.
Essentially, the popular theory -- that the pilots were unaware that the autopilot was overcorrecting in an attempt to cope with extreme ice buildup -- has been thrown into doubt.
In its final moments, the plane was going back and forth violently, possibly with multiple swings, and to say it simply went up, down, left, right, then crashed, may be too simplistic,CBS News correspondent Jeff Glor reported Monday based on late word from the Chealander.
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.
The latest devleopments raise new possibilities about why the plane went down, Glor reports.
The plane crashed belly first on top of a house Thursday night, killing all 49 people on board and one person on the ground.
Just before they went down in a suburban neighborhood near the Buffalo airport, 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.
The Dash 8 Q400 plane operated by Colgan Air was equipped with a "stick shaker" mechanism that rattles the yolk to warn the pilot if the plane is about to lose aerodynamic lift, a condition called a stall.
When the stick shaker engaged, it would have automatically turned off the autopilot, Chealander said.
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.
Investigators who examined both engines said they appeared to be working normally at the time of the crash, too.
In a December safety alert issued by the NTSB, the agency said pilots in icy conditions should turn off or limit the use of the autopilot to better "feel" changes in the handling qualities of the airplane.
Colgan Air operates a fleet of 51 regional turboprops for Continental Connection, United Express and US Airways Express.
Chealander said Colgan, like most airlines, had begun following NTSB recommendations that pilots use deicing systems as soon as they enter conditions that might lead to icing.
Federal Aviation Administration spokeswoman Laura Brown said the agency advises pilots to disengage the autopilot when ice is accumulating, but the guidance is not mandatory.
She also said some planes are certified to be flown on autopilot in icing conditions because doing so "may actually keep the aircraft at a steadier speed and altitude than a pilot could flying it manually."
Brown said the agency considered making the guidance mandatory, but others in the aviation community argued against it, citing the capabilities of such advanced planes.
She did not know if the 74-seat Q400 Bombardier aircraft that crashed Thursday was certified to be on autopilot during icing conditions.
By Sunday, authorities had recovered the remains of 15 people from the wreckage as crews raced to finish their work before a storm arrives later in the week.
Erie County Executive Chris Collins said recovery efforts intensified after the arrival of additional federal workers. A storm forecast for Wednesday added to the urgency.
The storm could hamper recovery efforts, but "the investigation will continue snow, rain or shine," said David Bissonette, the town's emergency coordinator.
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.