Acknowledging "security gaps" that could leave airliners vulnerable to a terrorist attack, the federal government is moving ahead with a new system that would allow shippers to screen cargo before it gets to the airport.

Transport Canada says the system would bring air cargo screening up to the standards of key trading partners and result in a net benefit to Canadians of $202 million over 10 years.

It would also represent a seismic shift in the way cargo is processed, entrusting known shippers with security screening that is now largely done by air carriers.

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In Canada, about half of all cargo that moves by air is carried on passenger flights — totalling more than 400 million kilograms annually.

In a regulatory plan, quietly published Saturday, the government says relying on carriers to screen all cargo for explosive devices would be "slow and impractical" and result in bottlenecks, delays and additional costs.

"Shippers need to be given the authority to screen their own goods," the proposal says.

"In order to do so, there must be a regulatory framework and program in place for the maintenance and enforcement of air cargo security that international partners will recognize."

The NDP and Liberal transport critics say that while there is a role for industry in air cargo security, the government must ensure proper oversight and accountability.

In his 2010 report on the Air India terrorist bombing, former Supreme Court justice John Major recommended urgent introduction of comprehensive air cargo examination.

Transport Canada has been consulting and drafting plans for years, mindful of threats like the October 2010 episode in which explosive devices were found in air cargo headed to the United States from Yemen.

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"Civil aviation remains a favoured target of terrorist attacks," says the newly published plan.

"Airports, aircraft and passengers offer the kind of high-profile targets that terrorists seek, and damage to a nation's civil aviation sector can cripple a nation's economy and sense of security."

The planned amendments would allow shippers, cargo companies, warehouse operators and trucking firms to take part in the program on a voluntary basis. Participation would require them to invest in secure facilities, do personnel background checks, ensure a secure chain of custody for goods, and implement training, screening and record-keeping.

The costs of participating would be offset by the benefits of avoiding screening fees and delays, says Transport Canada.

The department and other federal agencies have earmarked $17.5 million for inspector training, inspections, processing program applications and other administrative functions — though it appears the money would come from existing budgets.

Opposition MPs greeted the new plan cautiously, pointing out shortcomings with Transport Canada's oversight of rail industry safety.

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The move toward better air cargo screening and efficiency is welcome, said NDP transport critic Hoang Mai.

"The main question that remains is how it will be enforced," he added. "That's something that we will definitely keep a close eye on."

Liberal transport critic David McGuinty said he's wary of the relationship between Transport Canada and the industries it regulates.

"It seems very, very close. In fact sometimes it seems downright cosy."