FILE - In this Thursday, July 11, 2019 photo provided by Tim Tricky of the band Hurricane Fall, emergency workers treat a passenger on an Air Canada flight to Australia that was diverted and landed at Daniel K. Inouye International Airport 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 basically when two huge air masses close to each other are moving at different speeds. If the difference in speed is big enough, the atmosphere can’t handle the strain, and it breaks into turbulent patterns like eddies in water.