Canada plans to buy a handful of used Australian fighter jets as a stopgap on the way to replacing all of the air force's aging CF-18s sometime in the mid-2020s, the Liberal government said Tuesday.

Cabinet ministers at the same time formally announced the beginning of the competition to replace the entire fleet of fighter jets, a process that will take years.

The long-expected purchase of 18 warplanes puts an end to a bid for brand new Boeing Super Hornets, which had been the Trudeau government's initial plan over a year ago.

But the proposal went down in flames after the Chicago, Ill.-based aerospace giant launched its trade fight against Bombardier passenger jets.

No price tag was released in the formal announcement, which was made by Defence Minister Harjit Sajjan and Public Works Minister Carla Qualtrough.

Australia has made a formal offer that will be subject to negotiation, but the expectation is that the first "Classic" Hornets will begin arriving in January 2019.

Minister of National Defence Harjit Sajjan discusses the government's plan to replace Canada's aging fighter jets by the mid-2020s 8:39

The U.S. government will still have to give its blessing to the deal because the U.S. was the original manufacturer.

The Liberals said in the 2015 election campaign that they would not buy the Lockheed Martin-built F-35.

Mechanism to measure 'Canada's economic interests'

Angered by the Bombardier trade complaint, the Liberals have said Boeing was "no longer a trusted partner."

The complaint with the U.S. Commerce Department, alleging the Montreal-based aerospace-maker was dumping passenger jets into the American market at unfair prices, resulted in nearly 300 per cent import duties.

Despite that, senior officials speaking on background at a technical briefing Tuesday said no company will be excluded from the full fighter replacement program.

There is, however, one interesting, new aspect to that contest.

It involves the introduction of an additional assessment mechanism to measure each bidder's "overall impact on Canada's economic interests," said officials who spoke on background to CBC News prior to the announcement.

That means competitors will not only have to deliver billions of dollars in economic offsets in return for the specific contract, but also demonstrate their other business dealings benefit the country.

That is clearly aimed at Boeing.

"Bidders responsible for harming Canada's economic interests will be at a distinct disadvantage compared to bidders who aren't engaged in detrimental behaviour," Qualtrough said.

"We're hoping this policy incentivizes all suppliers to behave in such a way that they won't be at a disadvantage."

Public Services Minister Carla Qualtrough tells reporters how Canada will choose new jet fighters 1:42

Qualtrough said a contract award is anticipated in 2022 and the first replacement aircraft could be delivered in 2025.

In the meantime, the air force will use the Australian jets to meet its commitments.

Sajjan said those jets are urgently needed to help Canada cover a long-standing capability gap, referring to the government's claim that there are not enough jet fighters for the air force to carry out its NATO and NORAD duties at the same time.

"Our government will not risk-manage our national defence commitments."

Life span doubts

The Australian jets are nearly three decades old, roughly the same vintage as Canada's existing fighters and they have the same basic configuration.

They are, however, close to the "end of their useful life," according to a government background which noted that the fighters require "regular corrosion maintenance."

Defence experts in Australia told CBC News in October that the country had few customers for its used warplanes, and selling to Canada was easier than most other proposals.

General Jonathan Vance, Chief of the Defence Staff (left to right) Defence Minister Harjit Sajjan, Carla Qualtrough, minister of public services and procurement, Navdeep Bains, minister of innovation, science and economic development and Marc Garneau, minister of transport make an announcement on fighter jets at the National Press Theatre in Ottawa on Tuesday, Dec. 12, 2017. (Sean Kilpatrick/Canadian Press)

That's because the Pentagon will not require all sensitive technology to be stripped out of the aircraft. A recently retired NORAD commander said Canada has only so much room to manoeuvre.

"There are finite limits to how long you can extend the operational life of an aircraft and it is difficult to modernize an aging aircraft without adding too much weight," said former U.S. admiral Bill Gortney, in an interview published Tuesday by the Washington-based Woodrow Wilson Centre.

He also predicted that the stopgap purchase would not end Canada's difficulties in being able to generate enough aircraft for all its missions.

"This will assist with the capacity gap, but does not address the capability gap the RCAF faces today," said Gortney.

"It is more and more difficult to find spare parts for these older models," he said.

"Maintenance crews are forced to cannibalize some jets to keep others in the air. There are only so many times the lives of the current aircraft can be extended before putting the safety of pilots at risk."

The commander of the Canadian air force, speaking to CBC News prior to the announcement, said he has "absolutely" no safety concerns about the used jets.

Lt.-Gen. Mike Hood said they will, however, require a critical life extension to keep them flying until 2025, something the CF-18s have already been given.

"They would be brought up to exact same strict standards from airworthiness and flight safety standards as our present fleet," Hood told CBC News.