British Airways Flight 295 dropped about 27,000 feet in minutes after departing London Heathrow for Chicago, leaving passengers terrified as oxygen masks deployed and the aircraft descended to around 9,000 feet.

Passenger Gauri Jayaram described the terrifying moments aboard the Boeing 777, saying she could physically feel the aircraft descending rapidly before alarms sounded and oxygen masks suddenly dropped from the ceiling.

“I have never been in a situation where we’ve got oxygen masks hanging,” Jayaram said, describing the experience as unlike anything she had encountered despite traveling frequently.

Passengers were instructed to keep their oxygen masks on for around 30 minutes as the crew explained that the aircraft had lost cabin pressure. Flight attendants moved through the cabin checking that passengers, including a baby, were using the masks correctly.

After leveling off at about 9,000 feet, passengers were allowed to remove their masks. However, the ordeal continued as the aircraft turned back toward Heathrow.

The Boeing 777 spent several hours flying over England and the surrounding area while pilots prepared for an early landing. Fuel was dumped to reduce the aircraft’s weight, while the landing gear was lowered earlier than usual to help prepare for the landing.

Jayaram described the aircraft as shaky for nearly two hours and said the situation was intimidating.

British Airways confirmed that the incident was caused by a “technical issue” and said the aircraft eventually landed safely at Heathrow.

Jayaram had been traveling to Chicago for the Chicago Marathon but remained in London following the incident and was later rebooked onto another flight.

The incident is now raising questions about what caused the dramatic loss of cabin pressure and the rapid descent from cruising altitude.