Plane & Pilot
Tuesday, November 2, 2010

The Crosswind Component

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

A meteorological study found that there was well-defined mountain wave activity near Denver around the time of the accident. Winds reached 80 to 100 knots in the higher-elevation foothills west of the airport, with winds of 40 knots to 68 knots at the airport. The undulating motion of the waves resulted in strong, very localized, intermittent gusts at the airport's surface. In addition, investigators received a civilian report of a wind gust of about 50 miles per hour that lasted two to three minutes. It came from a couple driving a vehicle west of the airport. Further, an airline captain who was in a plane parked at one of the gates closest to the accident site told investigators that he heard a rumbling sound and felt the airplane shake as a result of a sudden increase in wind near the time of the accident. This captain saw debris blowing on the ramp and ramp personnel having trouble standing in the high winds. He estimated the wind gust speed exceeded 50 mph and lasted 45 to 50 seconds.

The Safety Board found that Continental's simulator training didn't replicate the ground-level disturbances and gusting crosswinds that often occur at or near the runway surface. The Board said it also wasn't likely that the accident captain had previously encountered gusting surface crosswinds like those on the night of the accident. The Safety Board concluded that the captain wasn't adequately prepared to respond to the wind and changes in heading encountered during the accident takeoff.

The Safety Board noted that although there are wind-detection sensors at various locations around the airport, only wind information pertinent to the runway being used was given to the pilots, in accordance with standard procedures. The Safety Board hinted that had the controller been required to give the captain wind reports from around the airport, he might have questioned whether runway 34R was the best one to use.

The NTSB determined that the probable cause of this accident was the captain's cessation of right-rudder input, which was needed to maintain directional control of the airplane, about four seconds before the excursion, when the airplane encountered a strong and gusty crosswind that exceeded the captain's training and experience. Contributing to the accident were an air traffic control system that didn't require or facilitate the dissemination of key, available wind information to the air traffic controllers and pilots and inadequate crosswind training in the airline industry due to deficient simulator wind-gust modeling.

A Piper PA-18 Super Cub had been on a local flight from a private airstrip at Wasilla, Alaska, so that the pilot could show a visiting friend some of Alaska's scenery. About 20 minutes after departure, the airplane returned to the vicinity of the airstrip. A witness said the pilot circled overhead once, then began an approach for landing to the south. The pilot had to correct for a left crosswind. The witness said that as the airplane passed over the approach end of the strip, it became unstable and drifted to the right toward trees. He said that just before the airplane touched down, the engine power increased, the nose went up and it began to climb. The airplane struck a tree and it crashed into the woods. The pilot was fatally injured, while the passenger received minor injuries. She told investigators that the pilot warned turbulence might increase as they got closer to the airstrip. She said that as they descended below the tree line, the left wing lifted and they drifted to the right, toward the trees. She said the pilot added full power and applied full-left aileron and up-elevator before they impacted the first tree.

The NTSB determined that the probable cause of the accident was the pilot's failure to maintain directional control while landing in a gusty crosswind.

In its Aircraft Operating Instructions, the manufacturer of a special light-sport aircraft says this: "Takeoff and landing with crosswinds require a lot of training and experience. The greater the crosswind component, the more experience is required."

The NTSB didn't come up with a wind reading at the time this LSA struck terrain during an attempted go-around on runway 25 at Sky Manor Airport, Pittstown, N.J. However, at an airport 15 miles to the east, the wind was from 200 degrees at 11 knots gusting to 18 knots. At an airport 19 miles south, it was from 230 degrees at 15 knots, gusting to 21 knots. The pilot told investigators that according to the airport windsock, the wind was pretty much straight down the runway.

After touchdown, the left wing lifted up, and the airplane began to turn to the right. The pilot said that aileron and rudder couldn't correct. The pilot then added power in an attempt to abort the landing. The propeller struck the ground, and the airplane ran off the right side of the runway. The propeller blades, left main landing gear and left wing tip were damaged. Both occupants escaped injury.

The NTSB determined that the probable cause of this accident was the pilot's inadequate compensation for the crosswind during landing.


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