Three passengers on board an Air India flight from Amritsar to New Delhi were injured when the aircraft encountered severe turbulence on Thursday, reported NDTV on Sunday. The inner part of a passenger window fell off during the turbulence and a few overhead oxygen masks even fell open.

Air India, aviation regulator Directorate General of Civil Aviation and the Aircraft Accident Investigation Board are probing the incident, reported PTI. The aircraft was carrying over 240 passengers.

The Boeing 787 Dreamliner (VT-ANI) experienced turbulence due to bad weather for 10-15 minutes, reported PTI. The aircraft was at an altitude of 15,000 feet.

Preliminary data indicated that passengers on the airliner encountered up to three times the force of gravity “at an altitude of 18,000 feet-32,000 feet during the climb phase of the aircraft,” shortly after take off from Amritsar, according to NDTV. The turbulence was so strong that the auto-pilot systems in the cockpit tripped after exceeding their design tolerances, forcing the pilots to take manual control of the airliner.

Senior Air India air safety experts looking into the incident said “clear air turbulence appears to the preliminary cause”, according to NDTV. “Meteorological reports are being collected. No weather phenomenon of this sort was predicted on the charts.”

An unidentified official said, “The turbulence on AI 462 was such that the head of a seated passenger, who possibly did not have his seat belt fastened, hit the overhead cabin because of a bump”, according to The Times of India.

A senior Air India official told The Times of India, “This was a freak high level turbulence.”

One of the injured passengers received stitches after the aircraft landed safely at Delhi’s Indira Gandhi International Airport. Two others suffered minor injuries. “All the injured passengers took their connecting flights after receiving first aid,” the official said.

A video clip released by ANI shows an air hostess trying to fix a part of a passenger window that fell apart in the turbulence.

In October 2014, a Singapore Airlines flight was hit by sudden turbulence when it was descending to land in Mumbai, injuring 22 passengers and crew.