Cessna Rattled By Extra Large 747's Wake
November 29th, 2006 12:07 PM PDT
It's big, it's ugly and it nearly took out a small plane that got too close.
The Boeing Co.'s Large Cargo Freighter, a modified 747 that will be used to ferry sections of Boeing's 787 Dreamliner, left a wake vortex so powerful that it apparently sent the small plane plunging toward the earth as it prepared to land at Boeing Field.
The single-engine Cessna was being flown by a student pilot, but an instructor took over and regained control, avoiding a crash. By then, however, the Cessna was below the level of the booms of the cranes that are used to load and unload container ships at Harbor Island at the mouth of the Duwamish River.
"It was a pretty impressive job of flying," said a pilot who is familiar with the Nov. 16 episode.
Both planes landed safely, and no one was hurt, but the National Transportation Safety Board and the Federal Aviation Administration are investigating.
Based on information in a preliminary report from the NTSB, the wake vortices left by the Boeing plane may have been blown by a crosswind into the path of the Cessna 172.
Boeing Field, formally known as the King County Airport, has two parallel runways. The longer runway is used by bigger jets and the shorter one is used by small planes such as the Cessna. The Large Cargo Freighter was on approach to the longer runway when it zipped past the Cessna, which was lined up to land on the shorter runway.
The Cessna was at about 1,000 feet and was making a straight-in approach under visual flight rules to Runway 13 left when it apparently encountered the wake of the Boeing jet, the NTSB said.
The Large Cargo Freighter had been cleared for a visual approach to Runway 13 right.
Some five seconds after the faster Boeing plane passed it, the Cessna "rolled almost instantly to a 90-degree right bank and descended in a nearly straight nose-down attitude. The instructor took control of the aircraft, which was able to complete a recovery approximately 150 feet above the channel of water that runs along the east side of Terminal Island," the NTSB said in its preliminary report. "The recovery was completed below the level of the booms of the cranes that were unloading the nearby container ships."
The safety board said there was a 9-knot crosswind blowing about 80 degrees from the right of the path of both planes.
Boeing told investigators that the Large Cargo Freighter, which will have a maximum takeoff weight of about 800,000 pounds, weighed about 633,700 pounds at the time it passed the Cessna on final approach to the airport. It is expected to be certified with a maximum gross landing weight of 575,000 pounds.
"The Large Cargo Freighter was on an approved flight path - it was where it was supposed to be when it was supposed to be there," a Boeing spokesman said.
Allen Kenitzer, a spokesman for the FAA's regional office, said air traffic controllers issued a required wake turbulence warning as the Boeing jet approached the airport. The pilots of the Cessna acknowledged the wake advisory and said they had the 747 in sight, Kenitzer said.
The small plane is owned and operated by Galvin Flight Service. The flight instructor works for the company but she was not available Monday for comment. A spokesman said any information about the event had to come first from the owner of the business, and he was out of town.
Boeing uses the King Country airport as the delivery center for many of its commercial jetliners. The airport is also home to many corporate jets. Pilots who operate small planes from the airport know all about the dangers of wake turbulence created by the bigger planes.
"Everyone knows to keep their distance," said one pilot who asked not to be quoted by name. "It's a way of life around here."
The Large Cargo Freighter has become a common sight at Boeing Field the past few months. It is in the final stages of a flight test program leading to its airworthiness certification in early 2007. It has the same length fuselage and wingspan as that of a 747-400 freighter.
But modifications to the upper fuselage increased the cargo capacity to about 65,000 cubic feet, or about three times that of the 747-400 freighter.
Boeing will use at least three and possibly four Large Cargo Freighters to transport the wings and fuselage sections of the 787 from various manufacturing sites around the world to Boeing's Everett plant for final assembly of the Dreamliner starting next year. A second Large Cargo Freighter is being modified in Taiwan.
This was the first such wake incident involving the plane since it arrived at Boeing Field this summer, Kenitzer said
