Winslow Wheeler, a former defence auditor in Washington, says anyone would be a "fool" to commit to the program before the multi-role jetfighter exits its testing and development phase in 2019.
Wheeler was among four witnesses to appear on Parliament Hill on Tuesday before a panel of New Democrat MPs, who interrupted their summer recess in an attempt to put last spring's incendiary controversy back on the public radar.
"The F-35 is only 25 per cent through its flight test program. That's only the preliminary flight tests. That's the laboratory testing," Wheeler told the four New Democrats.
"The more combat-realistic testing starts in 2017 and won't be finished until 2019. Anybody, including my country, who buys this airplane before then, is a fool because you don't know what you're getting in terms of performance. And you don't know what you're getting in terms of cost."
The Harper government plans to begin purchasing a handful of the radar-evading jets in 2016, but Wheeler testified that the country's defence needs might be better served by maintaining two separate fleets of fighters — something military planners have ruled out as costly and impractical.
His comments were echoed by former Canadian defence bureaucrat Alan Williams, who last spring wrote a scathing book that critiqued of the federal government's management of the program. The procurement that could cost taxpayers between $25 billion and $40 billion over 30 years.
"Typically in Canada, with our limited budgets, we try to shy away from products that are being developed, products that are paper products," said Williams who headed the defence materiel group until 2005.
"We would much prefer to buy products that have already been established, where the (research and development) we know has been successful, as opposed to spending a lot of our money on research and development, which is so limited; with the risks that that money won't be properly used."
An expert in defence procurement, Philippe Lagasse of the University of Ottawa, said he's worried the Harper government is plunging head first into a costly program when it has not laid out in detail the reasons the air force needs a stealth fighter.
"All defence procurements must be linked to government policy," he told the MPs.
"Thus far there has not been a clear statement of what defence policies and priorities are guiding the procurement of the CF's new fighters."
Conservatives argue that their Canada First Defence Strategy is such a policy document. But critics argue it is nothing more than a shopping list of equipment and doesn't spell out what potential threats the country faces and how the military is expected to deal with them.
Defence journalist Scott Taylor testified the F-35 is a weapon meant for conducting first strikes on potential adversaries and has a dubious potential as an interceptor in the skies over Canada.
Wheeler was even more critical, calling the emphasis on stealth technology a passing "fad" and tearing apart the capabilities of the fighter-bomber, which is expected to intercept threats coming into Canadian airspace and attack ground targets.
It doesn't carry out any of the functions particularly well, he said.
Last spring the auditor general tore a strip off the government, accusing National Defence of hiding $10 billion in continuing costs for the fighter and Public Works of not doing enough homework to justify the purchase.
Conservatives responded with a seven-point action plan that took responsibility for the plane away from defence, giving it to a secretariat at Public Works.
"We will not proceed with a purchase until the seven-point plan we have outlined is completed, including an independent verification of costs," said Chris McCluskey, a spokesman for Associate Defence Minister Bernard Valcourt in an email following Tuesday's hearings.
"Funding for a CF-18 replacement, including payments to the Joint Strike Fighter program under the MOU, has been frozen until the due diligence is complete and conditions have been satisfied. We will ensure that we have full confidence in the numbers before any decision to proceed is taken."
The government promised to deliver that independent cost estimate in June, but has yet to hire an outside auditor.
The government insists maintaining the F-35 will cost about $19,000 per flying hour — or roughly the same as the current fleet of CF-18s, which are due to retire in 2020.
Wheeler dismissed that as "utter foolishness" and pointed to figures from the Pentagon, which suggest maintenance on the software-dependant jet could be double that of existing jets.
A better comparison would be to contrast the F-35 with the U.S. Air Force's F-22 Raptor, which costs about $50,000 per flying hour to maintain.
New Democrat defence critic Jack Harris says the party organized the hearing, during Parliament's summer recess, in order to get the testimony of experts on the record.
"We will be referring to the testimony that was given here today. We will using that to reinforce the arguments that this government is not doing the right thing," said Harris.
Boeing, a rival aircraft-maker, was invited to participate but declined.
The manufacturer of the F-35, Lockheed Martin, was apparently aware of the meeting but didn't show up.
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