Boeing faces an uphill battle in getting the 737 Max certified again after two ill-fated flights that cost hundreds of lives.
The reduced capacity - WestJet, Air Canada and Sunwing have a total of 41 of Max jets in their fleets - means the likelihood of higher fares and less choice for passengers looking to travel this summer, said Fred Lazar, associate professor of economics at York University's Schulich School of Business.
Boeing shares were down almost five percent in afternoon action at $308.59 after the New York Stock Exchange halted trading for around 40 minutes.
The statement is a shift from Boeing's most recent stance on the status of its top-selling aircraft, that eliminated a target date entirely after timeframes repeatedly mapped out in 2019 were not met.
The 737 MAX has been grounded since March following two fatal crashes that killed 346 people.
In its statement, Air Canada said decisions about returning the jet to service would be based on its own safety assessment following "approvals by the FAA and Transport Canada".
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It will also make it harder for it to resume production later this year should the 737 Max be cleared by then.
Boeing has released a statement estimating that the ungrounding of the plane will take place during mid-2020.
The trial run is scheduled for Thursday at 1800 GMT, although "flight testing is dynamic, and the date could change due to weather and other factors", Boeing said.
Toward the tail end of 2019, Boeing had said that it was hoping to resume deliveries shortly. In fact, the opposite came true. "It is subject to our ongoing attempts to address known schedule risks and further developments that may arise in connection with the certification process. It also accounts for the rigorous scrutiny that regulatory authorities are rightly applying at every step of their review" of the plane's flight controls and pilot-training requirements. Getting that issue resolved has the potential to cause further delays.
Boeing said it will provide additional information with quarterly results next week.
It's more of a question of when the aircraft will return to service, rather than if.