NEW YORK (AP) — They literally do not see it coming.
“Clear-air turbulence,” which evidently jolted an Air Canada flight Thursday over the Pacific Ocean, strikes almost out of the blue, with no visible warning in the sky ahead. Even an aircraft’s radar cannot spot it coming.
Intense turbulence struck an Air Canada flight to Australia on Thursday and sent unbuckled passengers flying into the ceiling, forcing the plane to land in Hawaii. More than two dozen were taken to hospitals after it made an emergency landing in Honolulu.
The flight from Vancouver to Sydney encountered “un-forecasted and sudden turbulence,” about two hours past Hawaii when the plane diverted to Honolulu, Air Canada spokeswoman Angela Mah said in a statement.
Clear-air turbulence happens most often in or near the high-altitude rivers of air called jet streams. The culprit is wind shear, which is when two huge air masses close to each other are moving at different speeds. If the difference in speed is big enough, the atmosphere cannot handle the strain, and it breaks into turbulent patterns like eddies in water.
Another source of turbulence is masses of air that bob up and down in the atmosphere, somewhat like waves in the ocean. They can arise spontaneously or form as air flowing over mountains is forced upward, starting the up-and-down cycle.
Meteorologists cannot be of much help in warning pilots about where they willl encounter clear-air turbulence, says Thomas Guinn, a meteorology professor at the Embry-Riddle Aeronautical University in Daytona Beach, Florida.
“It’s probably one of the most challenging forecast problems we have right now for aviation meteorology,” he said.
Paul Williams of the University of Reading in England, who is working on forecasting clear-air turbulence, said some tests suggest that specialized radar-like devices could make the atmospheric disruptions visible to pilots. But the devices are expensive and very heavy, a drawback for airplanes, so they are not widely used.
According to the U.S. Federal Aviation Administration, turbulence of all kinds injures about 40 passengers and crew a year on average.