Intuitive fred888: 27 injured (some with broken bones) from clear air turbulence on Aeroflot plane

An Aeroflot plane bound for Bangkok encountered severe turbulence Monday that left 27 of its passengers injured, some with broken bones.The airline confirmed the incident was the result of clear-air turbulence, the most difficult type to detect. New research suggests transatlantic turbulence could become up to three times worse in the coming decades.
For nervous fliers, nothing about this research is reassuring. Clear-air turbulence strikes without warning and, because of climate change, is only going to get worse, reports CBS News correspondent Mark Strassmann.

The sudden drop on the Aeroflot plane came without warning and anyone not strapped down was shot toward the ceiling, then slammed against the aircraft floor. Video of the aftermath shows the plane scattered with debris.

Unlike conventional turbulence that occurs when planes fly near weather systems, clear-air turbulence happens without the presence of clouds. Making it nearly impossible for pilots to detect, until it's too late.
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Researchers predict major spike in transatlantic turbulence

Yes. I saw a stewardess hit the ceiling on a flight during the 1980s from Seattle to Kahului, Hawaii on Maui.

Especially over oceans you want to have your seat belt on loose whether the seat belt light is on or off always. If you have to go to the bathroom or walk around so you don't get blood clots in your legs that's a different thing. Just realize clear air turbulence the pilot cannot predict and there are no devices to see this when there are no clouds or storms nearby.