MONTREAL - Experts say a Sunwing flight that devolved into a raucous onboard party might have been halted mid-trip had certain aviation protocols been strictly followed.

Videos of the Dec. 30 charter voyage from Montreal to Mexico shared on social media show unmasked passengers in close proximity singing and dancing in the aisle and on seats as some clutch bottles of liquor, snap selfies and vape.

John Gradek, head of McGill University's aviation management program, says the captain has responsibility for the plane, including the decision to turn around or touch down early due to unruly behaviour or other breaches by passengers.

“Pilots basically have full discretion to manoeuvre the airplane,” Gradek said in a phone interview.

“He's the boss on board the airplane. It's his or her decision. But he or she does that in consultation with headquarters, in consultation with dispatch in Toronto.

“I'm guessing that Sunwing dispatch instructed them to continue on,” he added.

Sunwing declined to comment about the decision to keep flying, citing “active internal and regulatory investigations.”

The Toronto-based tour operator said in an email that passengers - some were Quebec-based social media influencers - violated aviation regulations and public health rules with “unruly behaviour,” prompting the internal probe.

The health and safety of crew and passengers is “always our top priority,” Sunwing wrote.

Transport Canada has also launched an investigation in conjunction with the federal health and public safety departments.

It warned that non-compliance with COVID-19 or air safety regulations can result in fines of up to $5,000 per offence. It also noted that anyone giving false information to a Canadian government official - on vaccination status, for example - could face fines of up to $750,000, six months in jail or both.

Louis-Eric Mongrain, who worked as a commercial airline pilot for 14 years before the pandemic hit, said the decision to halt the flight all comes down to risk assessment.

“If the safety of other passengers or other crew members is at stake, it's definitely necessary to divert the aircraft at that point if it's feasible,” he said in a phone interview.

“But that is assuming that passengers were told to stop their behaviour. If they weren't, that doesn't really apply.”

Rena Kisfalvi, president of the Canadian Union of Public Employees local representing about 1,000 Sunwing flight attendants, said that while things got out of hand, her colleagues told her the guests were never “aggressive.”

“This wasn't a catastrophic event,” she said in a phone interview.

“Were they non-compliant with vaping? Yes. Were they non-compliant with masks? Yes. Were they non-compliant with alcohol consumption? Yes.

“But when you're in the air and you're halfway to where you need to be, there's a lot of factors that come into turning that plane around or landing it immediately,” she said.

“I think it was a decision that they made as a crew.”

Sunwing proceeded to call off the 154-passenger return flight from Cancun that had been scheduled for Wednesday.

“Our decision to cancel the return flight was based on the group's refusal to accept all terms and our security team's assessment that non-compliance would be likely based on their previous disruptive onboard behaviour,” the airline said in an email.

The trip organizer, who identifies himself on social media as James William Awad, said in a blog post Thursday that he had initially agreed to Sunwing's terms, including that no alcohol would be served, all passengers would “remain seated and belted,” and multiple “in-flight guardians” would be on board.

But Awad said that “we couldn't conclude an agreement” because Sunwing refused to provide meals on the roughly five-hour journey.

Prime Minister Justin Trudeau weighed in Wednesday, saying he was “extremely frustrated” with the young travellers' choices and calling them a “slap in the face.”

Robert Kokonis, president of consulting firm AirTrav Inc., said he was “shocked” the plane did not return to Canada.

“The protocol for most carriers in a situation like that, where the cabin crew have lost control of the passengers on the flight, is to get the airplane put down as soon as possible. If they can make it back to Canada, great. If not, you set down at the closest airport where it would make sense,” he said in a phone interview.

This report by The Canadian Press was first published Jan. 6, 2022.