Severe Icing Probably Brought Down the Continental Commuter Flight

It looks like the tragic crash of a Continental Airlines commuter flight in New York may have been caused by structural icing:

Federal investigators said doomed Continental Flight 3407 experienced heavy ice buildup and lurched violently moments before it dove into a house near Buffalo, killing 50.

Data collected Friday from the plane's two black boxes "shows a series of severe pitch and roll excursions" shortly before the recording ended and the commuter jet crashed, said Steve Chealander, spokesman for the National Transportation Safety Board.

Minutes earlier, the pilots reported "significant ice buildup on the windshield and leading edge of the wings," Chealander said. They had already activated the de-icing mechanism on the aircraft just prior to their comments about the ice.

NTSB investigators retrieved both black boxes — the flight data recorder and the cockpit voice recorder — Friday morning and sent them to Washington, D.C., for analysis.

Fourteen members of the NTSB are working on discovering what brought down Flight 3407, Chealander told reporters.

The Continental commuter plane coming in for a landing in Buffalo dropped suddenly and dove into a house in snowy, foggy weather late Thursday night, about 5 or 6 miles from the airport.

All 49 people aboard the plane and one person in the home in the suburb of Clarence, N.Y., were killed.

The black boxes, which were "determined to be of good quality," recorded two hours of conversation, Chealander said.

The crew can be heard briefing each other about the weather in the cockpit, reporting a visibility of 3 miles with snow and mist in the area.

At 16,000 feet, "they noticed it was rather hazy and they requested a descent to 12,000 feet," Chealander said.

Air traffic control gave them clearance. Shortly thereafter, they descended again to 11,000 feet.

"They discussed significant ice buildup on the windshield and leading edge of wings," Chealander said. "The flight data recorder shows the airframe de-ice was selected in the 'on' position prior to that."

One minute before the end of the recording, the landing gear was placed down. Twenty seconds later, pilots engaged the wings' flaps — a normal landing procedure.

It was then that they apparently lost control of the aircraft, as the data recorder showed the plane lurching wildly in pitches and rolls "within seconds of the flaps command," Chealander said.

The crew attempted to raise the landing gear and lower the flaps just before the tape went silent, he said.

For the non-pilot crowd out there, icing causes two problems. One is the added weight which can cause center-of-gravity problems with the aircraft. But more seriously, ice sticking to the leading edge of the wing and tail surfaces will actually change the aerodynamic shape of those surfaces causing a reduction in lift and an increase in the stall speed of the wings (the point at which the wing will no longer generate lift).

It looks to me that when the crew slowed down for their landing approach, the ice buildup was significant enough that the stall speed had increased above the normal approach speed of the aircraft. There wouldn't be any warning devices on the aircraft to tell them that. The wings stalled and the plane nosed over. They were unable to regain control as the plane dived toward the ground.

The report states that the deicing equipment had been turn on. On planes like this one it's usually a rubber boot on the leading edge that inflates and crack the ice causing it to break away. You can see the black deicing boots in this photo of a Q400, the type of aircraft that crashed:



If the deicing system wasn't working properly, or was turned on too late, the build-ups on the wing surfaces could have quickly become dangerous. Given the state of the remains of the aircraft, I'm not sure if they'll be able to determine how well the system was working.