United Airlines
United Airlines flight traveling from Chicago to Montreal, Canada, was diverted to Buffalo-Niagara International Airport, Cheektowaga, New York. In this picture, a United Airlines jet taxis along a runway as another jet approaches its arrival at O'Hare International Airport in Chicago, Illinois, Oct. 5, 2006. Getty Images/ Tim Boyle

A United Airlines flight traveling from Chicago to Montreal, Canada, was diverted to Buffalo-Niagara International Airport, Cheektowaga, New York, on Wednesday after smoke was seen coming out of the cockpit, according to the Niagara Frontier Transportation Authority.

The plane was carrying 50 passengers and three crew members at the time and landed safely at the Buffalo airport at 4:22 p.m. EDT, local news outlet the Cheektowaga Chronicle reported. Firefighters immediately surrounded the plane after it landed. Passengers had to spend 6 hours at the airport while waiting for the aircraft to be readied.

United Flight 3968 was delayed by 6 hours 36 minutes. Instead of its scheduled 5:05 p.m. EDT arrival, it landed at Montréal–Pierre Elliott Trudeau International Airport at 11:41 p.m. EDT. The official reason stated for the delay on the airline's website was “aircraft maintenance.”

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On Tuesday, another flight of the same airlines made an emergency landing in Newark, New Jersey, after a “mechanical issue,” as the windshield in the cockpit seemed to have been shattered. There also appeared to be a medical emergency on the flight, the details of which were not available.

The passengers of the flight were provided rooms for the night and they departed on a new flight on Wednesday, CBS New York reported.

United Airlines flights have been diverted at least four times in the previous month. On July 19, flight UA907 traveling from Chicago to Frankfurt, Germany, landed instead at Dublin International Airport, Ireland, after a passenger onboard the plane fell seriously ill. Medical personnel rushed to the runway to tend to the passenger, the Independent reported. The identity of the passenger was not revealed.

On July 20, United Airlines flight UA125 was traveling from Athens, Greece, to Newark, New Jersey, when one of the crew members onboard noticed an issue with one of the engines of the flight. The affected engine was shut down and the flight was diverted to Shannon City, Iowa, Breaking News reported.

An airline spokesman apologized for the inconvenience caused to the passengers: "Our team at Shannon Airport is providing assistance to customers of United flight 125 from Athens to Newark, New York, which diverted to Shannon Airport because of a mechanical issue and landed safely. The flight was canceled due to the crew reaching their maximum duty time.”

"We are providing hotel accommodation as well as meal vouchers for our customers, and making arrangements for them to complete their journeys tomorrow. We have apologized to our customers for the inconvenience this caused,” he said.

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In another instance, an unruly passenger on United Airlines flight 898, traveling from Houston, Texas, to New Orleans, Louisiana, forced the plane to return to the airport it took off from. According to Eyewitness News, a woman began yelling and banging the walls of the plane.

"I hear (her) screaming, 'We are all protected and loved! We are all protected and loved! This plane is going to land beautifully and kindly!'" a fellow passenger who tackled her said. She had tried to access the cockpit of the plane. However, before she could do so, she was overpowered and restrained with zip-tie handcuffs, Eyewitness News reported.

“It took five men to hold her down. It wasn't easy. She was in a total psychotic state. She was very aggressive," the passenger added.

Law enforcement was called on the site after the flight landed and the woman was taken off the plane. The flight took off shortly after the passenger was removed.

Bad weather has also been a reason behind United Airlines flights being diverted. On July 28, a United Airlines flight was diverted to Cleveland, Ohio, instead of Washington D.C. due to unfavorable climate. Incidentally, it was also the first time that a United flight had landed in Ohio, NBC affiliate WKYC reported.