There's little wiggle room to prolong the life of Canada's CF-18 jet fighters beyond 2020 and they may have to be flown gently if there are further delays in the F-35 program.
A Defence Department chart that tracks maintenance on all 77 aircraft shows the CF-18s had used up about 73 per cent of their airframe life prior to last year's Libya bombing campaign.
National Defence has acknowledged there is no back-up plan if the multi-national F-35 stealth fighter program encounters more problems or postponements.
The retirement date for all but three of the CF-18s is set at 2020, according to the spreadsheet tabled in Parliament last year in response to written questions by Opposition parties.
On average, each aircraft is expected to end its service life with just over 7,000 hours in the air; most had already surpassed an average 5,151 hours at the time the snapshot was taken in late 2010.
The aging fighters have gone through a decade-long $1.8-billion upgrade to their weapons systems and sensors, and senior defence officials say they'll "easily be effective" for another eight years.
All of the jets were purchased between 1984 and 1989. Aircraft No. 925 is expected to clock out with the airtime at 8,637 hours, according to the documents.
The first of the problem-plagued F-35s is supposed to be delivered in 2016, with the bulk of the planned 65 aircraft arriving in 2020.
The New Democrats say it's foolish that the Harper government has not prepared a solid back-up plan, even if that contingency is simply investing in some sort of airframe life-extension.
"The way they are proceeding simply confounds me," said NDP critic Matthew Kellway. "I don't know how they could have painted themselves into this corner without a back up, and if they have one they refuse to tell us what it might be."
But for the Harper government, the figures underscore the need to replace the aging fighters.
"Canada's CF-18s are nearing the end of their usable lives," said Chris McCluskey, a spokesman for Associate Defence Minister Julian Fantino.
"We have set a budget for replacement aircraft and we have been clear that we will operate within that budget. We will make sure that the Air Force has aircraft necessary to do the job we ask of them."
Other nations, notably the United States, have invested in programs to keep their F-16 Fighting Falcons and F-15 Eagles flying because of delays in the US $328-billion stealth fighter, which is the most costly weapons program in American history.
In fact, Lockheed Martin, which manufactures both the F-35 and the F-16, announced last week that it would offer upgrade kits to keep older Falcons in the air and might even build new ones.
Industry observers see it as a hedge against more possible delays.
The current Defence Department plan in Ottawa sees the first F-35s arrive in 2016 and enter service in the 2018 time frame, at which point the oldest of the current fighters would be retired. But development setbacks and delayed orders from other allied nations have cast doubt on that.
Defence experts have been pushing the government since last fall to consider a further upgrade to the CF-18s.
Retired air force lieutenant-colonel Dean Black has said it's something that should be considered rather than going down the road of Australia buying new Super Hornets, the beefed up version of the F-18.