Lt.-Gen. Andre Deschamps said the air force would have to review how much "concurrent activity" it could handle if the number of radar-evading F-35s drop below the 65 aircraft the government has promised.
"The air force will live with whatever the government procures for us," said Deschamps in an interview with The Canadian Press.
"In the end, it's all about managing risk in delivering the defence mission. The number 65 gives us the capacity to cover all our missions with confidence."
The minister in charge of buying equipment for the military, Julian Fantino, said in an interview with Montreal-based L'actualite that the number of stealth fighters Canada intends to purchase is not carved in stone.
"We still talk about it; it is (being) analyzed. There is still time, until 2013, to decide the final number," said Fantino, the associate defence minister. "Could be under 65? Maybe. At some point, we make a decision."
Deschamps acknowledged that the number of F-35s is "subject to review," but warned that the air force would be challenged to carry out missions "if the number of aircraft changes dramatically."
The Harper government committed itself in July 2010 to the current number of multi-role fighters, but does not expect to begin taking delivery until 2016.
It is the smallest fleet the air force is able to live with given its current commitments to North American air defence, which requires at least 36 fighters to be set aside for NORAD missions. The initial joint-strike fighter proposal said Canada was prepared to buy 80 aircraft, replacing the current fleet of CF-18s almost one-for-one.
Deschamps said the decision to move to 65 jets was based on a mixture of "affordability" and what numbers the air force believes "it needs to deliver on our numerous defence missions."
Both Fantino and Defence Minister Peter MacKay have insisted the $9 billion set aside for the initial purchase is a hard figure and will not be exceeded.
The price tag Canada and other nations will pay per aircraft is unclear despite intense speculation, and Fantino did not elaborate whether the Harper government could buy fewer F-35s.
The government has insisted it will pay roughly $75 million per aircraft when it begins placing orders for delivery in 2016.
But in figures released over the weekend for initial production batches, the U.S. and Britain are expected to fork out between $140.9 million and $144.9 million per aircraft.
The price tag fluctuates year-to-year, depending on the number of aircraft ordered. If the current figure holds, the government would be forced to either take fewer planes — or increase its capital budget.
Matthew Kellway, an Ontario New Democrat MP, said he sees Fantino's comments as the government's back-door admission that it can't meet its target and that critics were right in focusing on the enormous cost.
"It's an acknowledgment they can't get the plane for the number they said they could," he said. "I think just about everybody else in the world has acknowledged that is the case."
The Norwegians have been more pragmatic by laying out a range for the F-35 price, Kellway said.
There has been speculation in the defence community that a potential shortfall in manned stealth fighters could be made up with the planned Harper government purchase of unmanned aircraft, such as the U.S.-made MQ-1 Predator.
But Deschamps says drone technology, while rapidly evolving, does not allow it an air-to-air combat role, which is the primary requirement of the stealth fighter.
He also questioned the ability of remotely-operated aircraft to conduct air-to-ground attacks against heavily defended targets.
Currently, drones do an excellent job in surveillance and strikes against targets that don't shoot back, said the air chief.
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