A Seattle air traffic controller spotted a heavily loaded 747 crossing paths with an Air Canada jet just moments before the Canadian aircraft was thrown out of control at 35,000 feet, injuring 10 passengers.According to sources close to the investigation, the Seattle controller ordered one of the planes to change altitude after noticing that the 747 was crossing paths with Air Canada Flight 190, an Airbus A319 en route from Victoria to Toronto Jan. 10 carrying 83 passengers and five crew members.Moments after the controller issued his order, the Air Canada jet was pitched into a series of rolls and dives that threw passengers around the cabin and caused undetermined damage to the airplane, which diverted to Calgary for an emergency landing.Although the planes met federally mandated separation requirements, the Seattle controller apparently believed weather conditions in the area might cause the Air Canada jet to hit the 747's wake turbulence, a powerful vortex of air that trails behind an aircraft as it flies. "He thought it was a little tight for the conditions," a source said.Investigators with the Canadian Transportation Safety Board acknowledged that they are considering wake turbulence as a potential cause. Real Levasseur, the board's chief of investigations, said there is "a high probability that an external force may have caused the incident."Although the investigators have so far refused to elaborate, sources close to the investigation say the Seattle controller spotted the potential for a turbulence encounter between the two jets after noting that weather conditions were nearly ideal for the creation of mountain waves, invisible aerial currents that form downwind of hills or mountains. Because they contain wide bands of rising and falling air, mountain waves can make it difficult to predict how quickly wake turbulence behind an aircraft will dissipate.The incident took place in Washington airspace south of Cranbrook, British Columbia, an area noted for wave activity. It is popular with glider pilots, who ride the rising parts of waves to altitudes of 25,000 feet or more.Reports from investigators and from an airline pilot on the Air Canada flight as a passenger are consistent with a wake turbulence encounter, which commonly involves sharp rolling motions as an airplane enters the swirling air left behind by another aircraft. Transportation Safety Board investigators said the Air Canada jet was thrown sharply to the left and right, reaching bank angles as steep as 46 degrees -- about twice the normal limit for an airline flight.The pilot-passenger told colleagues on an aviation chat site that the aerial upset exceeded anything he had previously encountered. "All I know is that we were in smooth air in cruise when the plane rolled abruptly to the left followed by a roll reversal to the right," he wrote. "It was nothing that I have ever experienced before. It was a very violent disruption. As you can imagine anything that was not strapped down was airborne. I was lucky that neither I nor my family was hurt."(Distributed by Scripps Howard News Service, www.scrippsnews.com.)
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