Plane & Pilot
Tuesday, November 2, 2010

The Crosswind Component

The principle is the same whether you’re flying a 737 or an LSA

DIRECTIONAL CONTROL. A Continental Airlines 737-500 like this ran off the runway during a nighttime departure from Denver, Colo. The pilot failed to adequately compensate for strong crosswinds.
Contrary to what some pilots may think, an aircraft's maximum demonstrated crosswind component is only an operating limitation if the aircraft's manufacturer says so. It's not a limitation imposed by FAA regulations. During the type certification process, the FAA requires the manufacturer to demonstrate that its airplane can be controlled in 90-degree crosswinds up to 20% of Vso. The demonstration is performed by a test pilot who's not supposed to use exceptional skill or alertness. The FAA doesn't require that a manufacturer set limitations based on the demonstration, or even publish guidelines for gusty crosswinds that may briefly exceed the maximum demonstrated crosswind component. The need to know what their airplane will or won't do in crosswinds unites pilots of light-sport aircraft, jet airliners and everything in between.

The NTSB recently completed its investigation into the December 20, 2008, crash of Continental Airlines flight 1404, a Boeing 737-500 that ran off the left side of runway 34R during a night takeoff from Denver International Airport, Denver, Colo. A fire broke out. The captain and five of the 110 passengers received serious injuries. The first officer, two flight attendants and 38 passengers received minor injuries. The rest of those on board were uninjured. There were visual meteorological conditions with strong, gusty winds from the west, kicked up by nearby mountain wave conditions.

After the flight was cleared into position on runway 34R, the pilots completed the before-takeoff checklist. According to the cockpit voice recorder, the captain commented, "Looks like...some wind out there." The first officer replied, "Yeah," and the captain stated, "Oh yeah, look at those clouds moving." The wind as reported by the ATIS was supposed to be only 11 knots. But the local controller radioed that the wind was from 270 degrees at 27 knots, assigned a departure heading of 020 degrees and cleared them for takeoff. The wind as reported by the tower was well within the airline's crosswind guideline of 33 knots when using a dry runway. Boeing doesn't mandate a crosswind limitation.

The first officer acknowledged the takeoff clearance. As the airplane began to power up, the captain told the first officer, "Alright…left crosswind, 20, ah, seven knots...alright...look for 90.9 (90.9% engine power setting)." The captain told investigators that as the airplane accelerated, he shifted the primary focus of his attention from the thrust levers to outside visual references, keeping the airplane on the runway centerline. The first officer's attention was primarily focused on monitoring the engine instruments. The first officer told investigators that after the power was set, he shifted his attention to monitoring the airspeed so that he could make the standard airspeed callouts.

The flight data recorder (FDR) showed that as the airplane accelerated, right-rudder-pedal inputs increased, while the control wheel and column and their respective control surfaces were at their neutral positions. As the airplane accelerated through about 55 knots, the airplane's heading began to move left, and the FDR recorded the beginning of a large right-rudder-pedal input. At the same time, the control wheel was turned to the left. The nose of the airplane then moved right. The 88% right-rudder-pedal input then dropped to only 15%. After the airplane hit 85 knots, the nose started moving back to the left. Then, there was another large right-rudder-pedal input. At about 90 knots, the amount of right-rudder-pedal input again dropped, and it briefly went to neutral. The control wheel was turned from left to right. The first officer said, "Oh, [expletive]." The captain called for a rejected takeoff. FDR data showed engine power was reduced, brakes applied and thrust reversers deployed. The airplane ran off the left side of the runway about 2,600 feet from the beginning. It crossed a taxiway and an airport service road before stopping.

Both pilots told investigators there were a couple of "very painful" bumps before the airplane came to a stop. They indicated that they were dazed or "knocked out" for a minute or two.

The captain had more than 13,000 total flight hours. The first officer had about 8,000 hours.


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