Kate Major Arrest: She Terrorized Passengers and Flight Attendants ... Cops Say

A judge ordered Kate Major go straight to rehab after she was busted for threatening to slash someone's throat during a flight -- and it's pretty clear she was wasted before getting on the plane.

According to the criminal complaint, Michael Lohan's estranged wife started trouble before the flight took off ... bitching about having to put her seat forward. The situation quickly escalated in the air -- a witness told a crew member Major was harassing a passenger and was possibly drunk. Kate allegedly yelled the witness' wife was a "bitch," and then threatened to "slit her throat."

Flight attendants moved Kate to a different seat to keep an eye on her. When she asked for a glass of wine, the flight attendant refused. So, Kate whipped out her phone and started recording the flight attendant.

The last straw came when she allegedly threw the phone and then rushed at a flight attendant. A passenger had to step in to hold her back -- and that's when the pilot decided to divert the plane to New Orleans.

Kate was arrested at the airport and booked for interfering with flight crew members, a federal offense with a very stiff penalty -- up to 20 years in prison.