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The crew of doomed Continental Flight 3407 reported "significant ice build-up" on the aircraft's windshield and leading edges of the wings in the moments before it suddenly plunged into a Clarence Center house Thursday night, killing all 49 aboard and one man on the ground in a hellish fireball, according to the National Transportation Safety Board.

The flight data and in-flight voice recorders, salvaged late Friday morning from the tail of the nearly obliterated plane, were rushed to Washington, D.C., for analysis.

And by 5 p.m., NTSB member Steven Chealander announced that the "black boxes" already were yielding potentially important clues as to what brought down the commuter plane.

Chealander and other aviation experts cautioned against jumping to conclusions and that the investigation was just beginning into the nation's deadliest airplane crash since November 2001.

But the new details about ice and the steep descent of Flight 3407, coupled with information about Thursday night's weather conditions, seemed to suggest ice may be to blame.

"Significant ice buildup is an aerodynamic impediment," Chealander explained. "Airplanes are built with wings that are shaped a certain way, and ice can change the shape."

The NTSB also reported that the black boxes indicated that the Bombardier Dash-8's anti-icing system had been activated. The ice clearing system employs "pneumatic boots," which expand outward to push ice off the wing edges. But there was no indication yet as to whether the system was functioning properly on the plane.

Flight 3407, operated by Colgan Air, a feeder company to Continental, took off at 9:20 p.m. Thursday from Newark Liberty Airport headed for Buffalo Niagara International Airport. It was about two hours behind schedule.

High winds, with gusts as high as 60 mph, had prevented many aircraft from taking off from the New Jersey airport Thursday evening, according to Steve Coleman, a spokesman for the Port Authority of New York and New Jersey, which operates the airport.

"We had some significant number of delays because of the winds," he said. "Some were delayed up to five hours."

Piloting the 74-seat turbo prop was Capt. Marvin D. Renslow, 47, of Lutz, Fla., who had joined Colgan Air in September 2005. The first flight officer, Rebecca Lynne Shaw, 24, of Maple Valley, Wash., had joined Colgan Air in January 2008.

The plane was heading north and west toward Buffalo where a wild winter storm with slushy snow and heavy winds had struck, plummeting the abnormally warm temperatures that had enveloped the area Wednesday down to the freezing level by Thursday night.

According to the National Weather Service, the airport temperature was measured at 33 degrees shortly before 10 p.m.

Weather conditions were described as "light snow, fog and mist," with southwest winds of 17 mph and gusts up to 25 mph.

In the last half-hour of the doomed flight, the crew reported visibility was 3 miles and there was snow and mist in the air, the NTSB said. But as the plane descended toward Buffalo, the crew reported "hazy" conditions."

According to conversations recorded between air traffic controllers and Shaw, which were available on the Web sites www.youtube.com and www.liveatc.net, all was normal while the plane was at 2,300 feet and getting ready to position itself for landing.

Aviation experts said it is typical for the first officer to handle radio communications while the pilot steers the plane.

Neither the air traffic controller, nor Shaw, showed any hint of trouble in their voices.

Air Traffic Control: "Colgan 3407, turn left heading 310 (degrees)."

Shaw: "Left heading 310, Colgan 3407."

About 30 seconds later, air traffic control contacted the plane again.

ATC: "Colgan 3407, three miles from Klump (referring to a locater marker located near Roll Road between Shimerville and Thompson roads in Clarence, about 4.5 miles from the airport). Fly heading 260 (degrees), maintain 2,300 (feet) 'til established. Cleared for ILS (instrument landing system). Runway 2-3 approach."

Shaw repeated the directions for getting the plane in place for landing in rapid-fire pace. The exchange was routine protocol, which gives air traffic controllers the chance to catch any mistakes.

About 30 seconds later, another back and forth from the tower to the plane.

ATC: "Colgan 3407, contact tower 120.5 (radio frequency). Have a good night."

3407: "(garble) Colgan 3407."

Then, just a second or two later, air traffic control tried to contact Flight 3407, likely to let the crew know they were cleared to land.

ATC: "Colgan 3407, approach?"

There was no response.

Five seconds later, he tried again.

ATC: "Colgan 3407, Buffalo."

Nothing.

A sense of urgency seemed to seize the air traffic controller, his voice growing loud and stern.

ATC: "Colgan 3407, approach?"

Silence. The air traffic controller asked another plane in the air for help locating the plane.

ATC: "Delta 1998, look out your left side about five miles for a Dash 8. Should be 2,300 feet. See anything there?"

Delta 1998: "Uh, negative."

The air traffic controller kept trying to reach the missing plane on the radio.

ATC: "Colgan 3407, Buffalo."

Another minute and a half pass.

ATC: "Colgan 3407, Buffalo tower. How do you hear?"

A supervisor is then heard over the radio.

ATC: "This is ground communication. We need to talk to someone at least five miles northeast, possibly Clarence, that area right in there, Akron area. Either state police or sheriff's department. We need to find out if anything's on the ground. This aircraft was five miles out. All of a sudden we have no response from that aircraft."

A moment later, another voice from air traffic control.

ATC: "All I can tell you is that we had an aircraft over the marker and we're not talking to him now."

Flight 3407 had in fact tumbled from the sky, crashing nearly nose first into a house at 6038 Long St. in Clarence Center.

The black boxes recovered by NTSB investigators indicated that, during its descent, the crew asked air traffic control for permission to drop down to 12,000 feet. It's not clear when this request was made. Moments later, it requested a flight path at 11,000 feet to dodge weather conditions.

The NTSB also said black boxes showed that, a minute before the plane crashed, the landing gear was engaged. About 20 seconds later, when the plane was at 2,200 feet above sea level, the aircraft experienced "severe pitch and roll," violent sideways and up and down motions, Chealander said Thursday.

The fiery impact, which sent raging flames shooting at least 50 feet up into the air, killed all of the crew and passengers on board, along with Douglas C. Wielinski, 61, who was inside the Long Street house. His wife and daughter survived.

Amazingly, the damage was limited to just the one house, although 12 residences nearby were evacuated as a precaution. NTSB officials said the steep angle of the crash likely helped limit the carnage on the ground.

Within just a couple of minutes of the crash, it was evident from the air traffic control recordings that they suspected weather could be a factor.

Air traffic controllers began quizzing other pilots about the icy conditions over Buffalo.

"Delta 1998, you getting any icing where you're at?" one Buffalo air traffic controller asked.

"We picked it up on the way down," the pilot reponds. "I don't think it's building any more here but about 6,500 (feet) down to 3,500 (feet) maybe."

Over the next several minutes, several other pilots chimed in.

"We're picking up ice here for a while," one pilot told the tower at Buffalo Niagara International Airport.

Another reported: "It doesn't appear to be building. We've got about a half-inch, well . . . about a quarter-inch of ice from the descent that has remained with us the whole time."

"We've been picking up rime ice for the last 10 minutes or so," added another pilot heading into Buffalo. Rime ice is an icy glaze caused by freezing water droplets that harden upon impact.

Icing is an especially dangerous condition that pilots face -- especially in the winter, according to Bob Miller, who operates Bob Miller Flight Training Inc. at Buffalo-Lancaster airport.

"When you're looking up at clouds, you're looking at microscopic water droplets," he explained. "In the wintertime, they're . . . below freezing but in liquid form. When they impact an object that is below freezing (such as an airplane wing) at that very instant, those liquid water droplets set up in solid form."

Miller emphasized that there's no way to know for certain whether icing caused the crash yet.

But he said there are two possible scenarios: icing of the back wing and icing of the main wings. Both would cause changes to the aerodynamics of an aircraft.

Icing on the rear wing would cause the plane to go off balance.

"The nose would drop very quickly," he said.

Icing of the main wings would cause the plane to stall, he said of the other scenario. In this case, the plane would pitch forward as well.

He said he did not suspect engine failure because there was no communication between the tower and the plane about such an issue.

Miller said whatever happened, it must have happened extremely quickly.

"There was no distress call. That is what is so extremely baffling."

Robert J. McCarthy, Dan Herbeck and Steve Watson contributed to this report.

e-mail: mbecker@buffnews.com

pfairbanks@buffnews.com

and slinstedt@buffnews.com

***

Bombardier Q400

Wingspan: 93ft. 3 in.

Length: 107ft. 9 in.

Height: 27ft. 5 in.

Max range: 1,298 nm

Cruise speed: 414 mph

Max landing weight: 62,000 lb.