A drunk passenger caused a ruckus aboard an Alaska Airlines flight — allegedly groping his seatmate, lighting up a cigarette and telling her, “We’re all going to die” – before he was restrained by two off-duty cops.

Adam David Seymour, 37, was flying from Seattle to Anchorage aboard Flight 49 on April 5 when he began harassing a woman who had initially found him to be friendly, according to a criminal complaint obtained by The Post.

The woman, identified as D.S., said Seymour’s grotesque behavior started shortly after he pulled three travel-sized bottles – colored pink, green and blue – from the seat pocket and drank something from the green one, the document said.

He then ordered and drank two bottles of Jack Daniels with Coke, after which “he started slurring his words, began moving physically closer to D.S., rubbed her lower thigh and knee on the inner and outer areas without her consent and tried to rest his head on her shoulder.”

Seymour allegedly made several comments about her sexuality, including that he thought she “looked like a lesbian,” and talked about licking her “down there,” according to the court filing.

The woman said she leaned away from Seymour and tried to ignore the sicko’s questions and sexual comments out of fear of triggering him further.

He then told her that “we’re all going to die,” as he gestured with his hands in a way she interpreted as showing the plane crashing, the document says.

As she tried to get the attention of the flight attendants, the suspect told her he “could p—- real good” and tapped his hand over a blanket that she placed on her lap – directly over her genitals.

“D.S. immediately closed her legs, leaned forward, and turned her back to him,” the document states. “A few moments later she heard a sparking sound and turned to see Seymour holding an ignited lighter and lit cigarette.”

When she told him smoking was not allowed, he allegedly said, “I’m a bad person.”

The desperate woman finally wrote a message on her phone and slid it to a man and woman sitting in front of her – and they turned out to be off-duty police officers.

After reading the plea for help, the male officer called a crew member who moved the woman to another seat.

But Seymour continued his unhinged behavior, threatening to kill a male passenger seated by the window, according to the court document.

The off-duty cops then restrained the suspect with flex cuffs and moved him to a jump seat, where he managed to break free before being tied again.

The man in the window seat told authorities that he observed Seymour manhandling the “clearly uncomfortable” woman.

After she was moved, the male passenger told Seymour to “stay in his lane. Sit down and shut up. Leave people alone,” the filing states.

“I’m going to kill you,” Seymour allegedly told him.

The suspect “groped me, assaulted a woman, threatened my life, and was clearly so wasted it was impossible to tell if he would explode,” the man said.

Two flight attendants stopped serving alcohol after they learned about the incident.

“He was obviously inebriated and snuck his own alcohol on the plane,” one of them said.

One flight attendant asked Seymour what he was drinking and he replied, “Hand sanitizer,” according to the filling.

Airport police in Anchorage swabbed Seymour’s hands, which triggered an alarm “for the presence of cocaine,” the affidavit said.

The suspect, who refused a Breathalyzer test, was charged Friday in Anchorage federal court with assault with intent to commit a felony.

He was transported to the Anchorage Correctional Center and has since been released from custody, the Alaska Daily News reported.

Alaska Airlines told The Post in an email: “On April 5, a guest caused a disturbance onboard Alaska Airlines Flight 49 that departed from Seattle to Anchorage.

“The situation was immediately contained, and the flight safely continued to its destination. The crew requested that law enforcement meet the flight upon arrival. The passenger was taken into custody by law enforcement authorities,” a spokesperson wrote.

In another incident involving Alaska Airlines, Chloe Dasilva, 32, was charged with one count of interfering with crew members after she allegedly threatened to kill a flight attendant.

She became “disruptive” during a Friday flight from San Francisco to Chicago and got into a profanity-laden confrontation with the male flight attendant, officials said.

Dasilva was restrained with zip ties and the flight diverted to Kansas City.

Last month, US Senate and House members proposed a new no-fly list for unruly passengers that would allow the Transportation Security Administration to ban people convicted or fined for assaulting or interfering with commercial airline crew members.