United Airlines Passenger Sues Claiming Airline Covered Up Shattered Window

United Airlines pilots had to deal with a shattered windshield at 40,000 feet, and although the airline said bird strike caused the emergency ... one passenger claims there was a massive cover-up.

United's flight 931 left Chicago bound for London on Oct. 27, 2018, and about 3 hours into the trip the pilot announced the windshield was splintered and they had to land immediately ... according to a passenger named Theodore Liaw.

In his lawsuit against United, Theodore says he and the other passengers aboard the damaged 767 had to "white knuckle" it for 30 minutes ... while the pilot and co-pilot rapidly went from cruising altitude to Goose Bay Airport in Newfoundland, Canada.

Theodore claims United's customer support agents told them a "bird hit the windshield," but he calls that a big fat lie, and claims he got the truth straight from the pilot during 8 hours on the ground. According to the suit, he asked the pilot and co-pilot if they'd hit something, and they "chuckled" and said that was impossible because "there's nothing alive at 40,000 feet."

In docs, obtained by TMZ, Theodore says the pilots openly confessed it was most likely caused by a mechanic over-tightening windshield bolts. They also admitted 2 of 3 layers of the glass were destroyed and they were nearly sucked out of the cockpit ... according to the suit.

Theodore is suing United for negligence. He says he hurt his back in the emergency landing and he's suffered horrible plane crash nightmares ever since the flight.