WASHINGTON — Pilot David Butler casually noted the blustery winds as he looked out a cockpit window of Continental Airlines Flight 1404 last December.
“Looks like you got some wind out here,” Butler told co-pilot Chad Levang as they waited for clearance for takeoff from Denver International Airport. “Oh yeah, look at those clouds moving.”
Thirteen minutes later, in the midst of a takeoff roll, the Boeing 737-500 with 110 passengers aboard suddenly veered left off a runway, rumbled across a field, and pitched into a ravine, where it broke apart and caught fire. There were no fatalities, but 37 people, including Butler, were injured.
A cockpit voice recorder transcript of Continental Airlines Flight 1404 was released today by the National Transportation Safety Board, along with other evidence gathered so far in an investigation of the Dec. 20 accident.
The board hasn’t yet reached a conclusion on what likely caused the crash, but aviation safety experts have suggested that a powerful crosswind may have weather-vaned the plane. That’s a phenomenon in which wind pushes an airliner’s tail hard enough to swing its nose into the wind, like a weather vane. The 737 is shorter than many airliners, making its rudder larger relative to the rest of the plane, experts said.
In an interview after the accident, Butler told investigators the plane was building up speed on takeoff when it turned sharply as if hit by a “massive gust of wind” or as if the tires had hit a patch of ice.
“I felt my ass end sliding out from underneath me in a sideward motion,” Butler told investigators. “The nose was pointing left, and the ass end was pointing the other way without any input on my part.
“My speculation is that we either got a big, nasty gust of wind or that, with the controls we had in, we hit some ice.”
Interviews with Butler and Levang are among documents made public in the National Transportation Safety Board investigation of the Dec. 20 accident. The board hasn’t reached a conclusion yet.
There were no fatalities, but 37 people were injured, including Butler.
Winds were reported at about 28 to 31 mph from the northwest with gusts up to nearly 37 mph just before the the Boeing 737-500 began a takeoff roll northward down a north-south runway.
Levang, who was watching airspeed indicators during the takeoff, estimated in an interview with investigators that the plane was traveling at about 100 mph when he noticed “a slight deviation to the left of centerline, but they were correcting back toward the right.”
“The next thing he knew was that the aircraft turned about 30-45 degrees to the left toward a black and yellow sign. From Mr. Levang’s perspective, there was ‘zero directional control,”’ according to an interview description.
Aviation safety experts have suggested that a powerful crosswind may have weather-vaned the plane, a phenomenon in which wind pushes an airliner’s tail hard enough to swing its nose into the wind, like a weather vane. The 737 is shorter than many airliners, making its rudder larger relative to the rest of the plane.
The crosswind limitation on takeoff for a 737 on a dry runway is about 38 mph — very close to the reported gusts at the time of takeoff, documents show.
Butler told investigators that if he had been concerned about his ability to take off safely in the reported crosswind, he would have requested a change of runway. Investigators said Levang told them he considered the crosswinds “definitely a manageable situation.”
Crosswind limitations are based on winds coming at a the side of a plane from a 90 degree angle, said aviation safety consultant Jack Casey, a former 737 captain. Because the winds were not coming directly from the side, Flight 1404 should have been able to tolerate a crosswind somewhat higher than its specified limitation, he said.
“I’ve taken off in those kinds of crosswinds all the time,” Casey said. “You don’t necessarily punt to the next runway, especially in a crowded airport like Denver.”
The documents said Butler acknowledged that when the plane began to veer left, as a last resort he reached down and grabbed the plane’s tiller for a second or two. He attempted to steer the plane back onto the runway using the tiller, but this did not work.
The tiller, similar to the power steering in a car, is very sensitive and is generally not used at high speeds, said Casey, chief operating officer of Safety Operating Systems of Washington.
“If the tiller were engaged at a high speed he could easily have compounded his direction control problems,” Casey said.
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