OTTAWA

The auditor general's office wasn't "nitpicking" when its probe into F-35 procurement found "significant things missing" from the government's life cycle cost estimates, the federal spending watchdog said Thursday.

"For example attrition, for example upgrades and the fact that these aircraft were going to last for 36 years, not just 20 years," Michael Ferguson told MPs on the public accounts committee examining his report into the stealth fighter program.

The feds have been using a 20-year life cycle in their $25 billion estimate for the cost of the jet, something Ferguson said appeared to be "normal practice" at the defence department.

But he added that according to the documents prepared by the department, officials "for the most part indicated they understood the life cycle of the aircraft were going to be at least 30 years."

He also pinpointed Public Works officials, who he argued didn't use sufficient due diligence when signing off on a sole-source potential purchase with little information from the defence department.

Ferguson's criticism built on his biting report released earlier this month, which concluded defence officials didn't adequately inform ministers about problems with the F-35 fighter program, underestimated expected costs and bent the procurement rules.

But on Wednesday, the watchdog refused to finger any politicians in the F-35 costing issues, saying he wasn't privy to the names of cabinet ministers who may have been aware of full life cycle costs.

"Those budgets were approved, they went through a formal process, but I certainly wouldn't have access to information about who saw what when," he said.

Still, he conceded the point from Tory MPs that F-35 figures were estimates - the jets have not been purchased - but noted even ballpark figures need to be calculated with the best and most precise information.

Next week, the public accounts committee will hear from senior officials from Public Works, National Defence, Industry, and the Treasury Board.