At least 27 people were hurt when an Aeroflot flight from Moscow to Bangkok hit a patch of severe turbulence.
No injuries were life-threatening, but several passengers suffered broken bones and three needed surgery, Russian officials said.
A passenger described being "hurled" up to the ceiling, trying to cling on amid shaking which "wouldn't stop".
The turbulence occurred in clear skies, which meant the crew were not able to warn passengers, the airline said.
"The reasons behind the injures were that some of the passengers had not had their seatbelts fastened," Aeroflot said in a statement.
'Impossible to predict'
Mobile phone footage of the aftermath of the incident showed injured people lying in the aisles, with packets of food and other items scattered on the floor.
"We were hurled up into the roof of the plane, it was practically impossible to hold on," a passenger who gave her first name as Yevgenia told Rossiya 24 by phone.
"It felt like the shaking wouldn't stop, that we would just crash," she added.
The pilot, Aleksandr Ruzov, said the turbulence was "impossible to predict", in an interview with the Russia 24 news channel.
He said the worst effects were felt at the back of the plane.
The incident took place about 40 minutes before the Boeing 777 carrying 313 passengers was due to land in Bangkok.
Twenty-four of those injured were Russians while the other three were Thai, the Russian embassy in Thailand said.
Fifteen people, including one child, were admitted to hospitals in Bangkok, a health ministry spokesman told the Russian news agency Interfax.
Three people needed surgery, two for multiple leg fractures and one for broken ribs, he said.
By early evening on Monday, 14 passengers remained in hospital, according to Aeroflot, which has said it will pay the medical costs of the injured.
The airline said the pilot's experience amounted to more than 23,000 flight hours and that about 750 cases of clear-air turbulence are recorded in civil aviation every year.
What is Clear Air Turbulence?
CAT - clear air turbulence - is turbulence that occurs in otherwise calm, clear blue skies, without any visual indication such as clouds.
It is caused when masses of air moving at different speeds meet, and can't be identified by the naked eye or conventional radar.
Pilots use reports from other aircraft, passed on via air traffic control, to keep track of patches of clear air turbulence.