A Vancouver-bound Air Canada flight forced to land at the Seattle-Tacoma International Airport due to mechanical issues has sparked a discussion about what domestic air passengers should know if they happen to land on U.S. soil without advance warning.

What was supposed to be a five-hour domestic flight from Toronto to Vancouver last Sunday turned into a 13-hour international ordeal for passengers.

But once the plane landed in Seattle, one passenger wondered aloud about the consequences for anyone carrying cannabis products.

Harold Wax, a security executive in the real estate sector, was one of 255 passengers aboard Air Canada flight AC125. Wax said as the plane was approaching Vancouver airport, the pilot came on and announced he had to abort the first landing attempt due to fog.

Problems with the auto-landing system led to a second failed attempt. Wax said the pilot informed passengers that because of the two failed attempts the crew would divert to Seattle to refuel, then return to Vancouver.

The flight path taken by an Air Canada 787 Dreamliner on Nov. 3, 2019 which tried twice to land at Vancouver International Airport but then headed to the Seattle airport where it finally landed. (FlightAware.com)

But when the plane reached Sea-Tac Airport, passengers learned the plane would be grounded for maintenance and they would have to disembark. Wax said that's when people aboard the plane became anxious.

"The passenger sitting beside me made a comment. She said 'I really wonder how hard it's going to be for passengers who don't have a passport to get into the U.S.''' Wax said.

"And I kind of chuckled and I said 'I hope nobody is carrying cannabis or CBD oil.'"

'Don't take a chance, dump your stash'

Immigration lawyer Richard Kurland warned Canadians who find themselves in a situation such as this that they should be prepared to ditch any cannabis products if necessary. He said U.S. officials are often willing to forgive possession of personal use CBD oil but even that isn't a sure bet.

"In cases where an emergency landing is required on U.S. territory, be aware that U.S. law will fully apply to you if you are transporting cannabis which may have been legal in Canada," said Kurland.

Air Canada passenger Harold Wax said his domestic flight to Vancouver was diverted to Seattle which caused concerns aboard the flight over proper documentation and cannabis rules. (CBC News)

He said the airline should inform passengers if their flight is going to be diverted to an airport outside of Canada — to give them time to dispose of any cannabis products.

"The best practical advice is queue for that washroom and the flight attendant should keep that washroom available to passengers who may need to dispose of any cannabis product in their possession."

In terms of identification needed to cross the Canada-U.S. border, Kurland said in this type of situation, a passport might not be needed. "There is no need to carry every last candlestick of ID with you aboard an airplane," he said.

In an emergency situation, current identification technology, including advanced biometrics is sufficient for Canadian travellers to be processed by U.S. border agents.

Air Canada responds

Air Canada said the 787 Dreamliner aircraft required a maintenance inspection in Seattle after developing a mechanical fault so the airline made an arrangement for authorities to enable passengers to "clear customs appropriately."

Air Canada spokesperson Angela Mah said in a written statement that there were no problems dealing with U.S. customs and extra airline staff members were scheduled to work to help passengers.

"We were advised there were no issues for any reason clearing the passengers from this flight."

Mah said the airline has a cannabis policy which states that in the event of a diversion, a passenger refused entry into a country because of cannabis possession is responsible for the consequences, including payment for the return trip home.

She said Air Canada regrets the inconvenience for last Sunday's delay, and is in touch with customers. She said passengers were provided with overnight hotel rooms, though some left for Vancouver by ground transportation.

Cannabis edibles, CBD infused gummies and other products were legalized in Canada on Oct. 17, 2019. (Shutterstock/Victor Moussa)

Harold Wax said upon landing, he didn't immediately see staff at the Air Canada counter, so he carpooled with other passengers to Vancouver.

He said the experience was an important reminder about what a worst-case scenario can look like.

"If you are flying on a domestic flight, you got to understand there's a chance that you might get diverted whether it's an emergency of a malfunction or something else.

"You could be diverted to the United States."