Canada's CF-18 fighter jets are due to retire in 2020. They need to be replaced, but no fully operational F-35s will be available by that date.

Stephen Harper has a decision to make: buy another model of fighter jet, or face a dangerous capability gap. He cannot expect our pilots to fly supersonic aircraft beyond their lifespan.

The Prime Minister, however, has been ragging the puck since April, 2012, when Auditor-General Michael Ferguson reported that the government had misled Canadians about the cost of the F-35s.

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In March, 2011, the Department of National Defence told Parliament the F-35s would cost $14.7-billion, including maintenance and operations. Internally, however, both the Department and Cabinet were working with a number of $25-billion.

The Auditor-General's report caused a storm of controversy, which Mr. Harper quelled by instructing the Royal Canadian Air Force to re-evaluate its options to replace the CF-18s. He set up an "Independent Review Panel" to monitor the Air Force's progress on the file.

The re-evaluation is now complete, though not yet public. Last month, the Air Force briefed deputy ministers on its findings.

The report is supposed to assess the cost, capabilities, and strategic advantages of four models of aircraft: Lockheed Martin's F-35, Boeing's Super Hornet, the French-made Rafale, and the Eurofighter Typhoon.

If the report is objective, it will explain that the F-35 is an increasingly uncertain gamble. In the United States, the F-35 program is already seven years behind schedule and $163-billion over budget.

Frank Kendall, the Pentagon official in charge of procurement, has described the F-35 program as "acquisition malpractice" based on flawed assumptions, unrealistic estimates, and "a general reluctance to accept unfavorable information."

Many of the problems concern the 24 million lines of computer code in the electronics of each F-35. The Pentagon is gambling that the enhanced sensory awareness of the aircraft, along with a stealth design that seeks to deny that awareness to adversaries, will triumph over speed, agility and firepower in future aerial combat.

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It is a gamble because stealth requires compromises on other capabilities. The F-35 is actually slower, less manoeuvrable, has a shorter range, and carries fewer munitions than the three-decade old CF-18s.

Just last month, Mr. Kendall warned that the F-35 software was "behind schedule" and that reliability was "not growing at an acceptable rate." President Barack Obama has personally intervened, ordering the Pentagon to assemble a team of independent experts to study the software delays.

Additional delays have arisen from "significant findings" of stress cracks in the fuselage and engine mounts of test aircraft "that will require mitigation plans and may include redesigning parts and additional weight."

The problems help explain why the U.S. government is slowing down its acquisition of F-35s, purchasing just 34 of the aircraft in 2014-15, eight fewer than originally planned. These will be test aircraft, useful for training but unsuitable for combat.

Under these circumstances, Canada cannot realistically hope to receive a fleet of fully operational F-35s within the next decade. And there's the rub.

The CF-18s were initially due to retire in 2002, but $1.8-billion in upgrades stretched their life expectancy to between 2017 and 2020.

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This deadline has been confirmed by Department of National Defence documents obtained by journalists through Access to Information requests. One e-mail from September 21, 2011 states: "The planned CF-18 estimated life expectancy is currently 2020."

The Independent Review Panel overseeing the Air Force's evaluation of possible fighter replacements has requested an assessment of how long the CF-18s could be kept flying, including through further upgrades. But fighter jets are subject to extreme forces during tight turns and at supersonic speeds, raising serious concerns about metal fatigue.

Our CF-18 pilots could be ordered to go easy on the aircraft. But while that approach might work for training, it would be suicide in combat. A training-only fleet of fighter jets is about as useful as an armoury full of blanks.

The Prime Minister is left with two responsible options. He could ditch the F-35 and launch an accelerated competition among the alternatives, with a view to receiving the first fully operational replacement aircraft by 2017.

Alternatively, he could sole source a small number of Super Hornets, which are the latest version of the CF-18s and therefore easily integrated into the Air Force's existing training, operations and maintenance regimes.

An infusion of Super Hornets would ensure the continuation of Canada's fighter jet capability until the F-35 either proves itself, or fails definitively. It would also provide time to observe the progress of other technologies such as drones, which at some point will render piloted fighter jets obsolete.

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Either way, Stephen Harper has to buy some fully operational fighter jets, and quickly – before the Royal Canadian Air Force loses its teeth.

Michael Byers holds the Canada Research Chair in Global Politics and International Law at the University of British Columbia.