The Liberal government's plan to keep a number of its CF-18 fighters flying through the 2020s — possibly up to 2032 — is a "high-risk" and "costly" option, according to an internal government report obtained by CBC News.

The technical engineering assessment was written for the material group at National Defence in the run-up to the former Conservative government's decision two years ago to extend the life of the front-line jets until 2025.

It raises questions about the serviceability and survivability of the aging fighters at the crucial transition time when the Liberal government hopes to bring a replacement on line.

The report takes on fresh relevance in light of the government's decision last week to postpone holding an open and transparent competition for a new fighter. Bidding is not expected to start until next year after the new defence policy has been released and could take up to five years.

The analysis has the Opposition Conservatives wondering why the Liberal government is not proceeding directly to the competition it promised in the last election.

National Defence says it intends to buy up to 18 Boeing Super Hornets as a stopgap measure until a brand-new fleet arrives.

The analysis is also significant considering this week's fatal crash of a CF-18 at a training range near Canadian Forces Base Cold Lake in Alberta.

Defence Minister Harjit Sajjan announces the purchase of 18 Super Hornet fighter jets 0:50

Defence Minister Harjit Sajjan last week said permanent replacements for the '80s-vintage jets "will be fully operational in the late 2020s."

That is further into the future than the former Conservative government had planned.

"That means we must continue to fly the legacy CF-18s throughout the 2020s, no matter what," Sajjan said during the news conference announcing the government's decision.

'A high-risk solution'

The Conservatives had planned to refurbish the fighters to keep them operational until 2025, something the internal analysis says results in "a reasonably low to moderate technical and operational risk" in light of the fact the U.S. navy intends to keep flying some of its F-18s and Super Hornets during the same timeframe.

It is after 2025 that the significant concern emerges.

The CF-18s would require a major overhaul — known as a Control Point 3 life extension — to remain operational after that date.

"This option is a high-risk solution, from both a technical and operational perspective," says the 13-page, unredacted evaluation.

"A majority of the fleet (50 aircraft) would need to be flown beyond the currently certified safe life."

The assessment goes on to list the components that would need replacing, and the list is extensive.

"A large and costly procurement of new wings and flight controls would be required to support this effort, as the structural lives of these components would expire for many of the fleet's aircraft."

Shortage of spare parts, weapons

The report also notes, among other things, that the fighter jets' transponders, which identify them as friend or foe to other aircraft, will have to be upgraded.

The avionics system will be considered outdated by the early 2020s and won't meet U.S. requirements for encrypted communications, which threatens operations with the Americans and the North American Aerospace Defence Command (Norad).

"From an operational perspective, the fleet will be exposed to a more lethal threat environment," says the analysis. "In addition there will be decreased interoperability with newer aircraft flown by Canada's allies."

The further into the decade the fighters operate, the more concern there will be about access to weapons and spare parts, the report adds.

$400-million upgrade needed

In an interview with CBC News, Sajjan downplayed the analysis, saying the Liberals have conducted their own, more recent studies that give them comfort.

"The engineers have assured us the life extension can be done in high confidence and we can meet our needs," he said, adding that concern about the overall condition of the fleet is one of the things that drove the Liberals to recommend the interim purchase of Super Hornets.

"Yes, we can extend our fighters to 2025. After that time they will be slowly graduated out."

Conservative defence critic James Bezan said the Liberals are stalling.

"We know Denmark just did a competition in 11 months. Norway did theirs in about a year and a half. Japan did theirs in a year and 11 months," he said. The Liberals "could do an open and fair competition right now and get a plane faster than they can in five years' time."

The refurbishment to 2025 is estimated to cost $400 million, but Sajjan was unable to say how much more it will be to keep the fighters flying beyond that date.

Unpublished, internal defence estimates shown to CBC News suggest the total overhaul cost could rise to $1.3 billion depending on the upgrades selected by air force planners.

In the last election campaign, the Liberals promised to buy a cheaper fighter in an open competition and plow the savings back into rebuilding the navy.

With an interim purchase of Super Hornets and a life extension program, the government will be hard-pressed to find savings.

"Yes, we are investing more. This option costs more money, but this is the situation we were dealt with," said Sajjan.