A leading Israeli airport security expert says the Canadian government has wasted millions of dollars to install "useless" imaging machines at airports across the country.

"I don't know why everybody is running to buy these expensive and useless machines. I can overcome the body scanners with enough explosives to bring down a Boeing 747," Rafi Sela told parliamentarians probing the state of aviation safety in Canada.

"That's why we haven't put them in our airport," Sela said, referring to Tel Aviv's Ben Gurion International Airport, which has some of the toughest security in the world.

Sela, former chief security officer of the Israel Airport Authority and a 30-year veteran in airport security and defence technology, helped design the security at Ben Gurion.

He told MPs on the House of Commons transport committee via video conference from Kfar Vradim, Israel, that he wouldn't reveal how to get past the virtual strip-search scanners, but said he can provide briefings to officials with security clearance.

Canada this year bought 44 body scanners for major Canadian airports -- three of them for Vancouver International. Each machine cost $250,000 and is being use for secondary screening to detect non-metallic threats, unless the passenger prefers a physical pat-down.

CATSA, the Canadian agency in charge of screening airline passengers, declined to provide comment on Sela's analysis.

Junior Transport Minister Rob Merrifield, who is responsible for the agency, defended the $11-million investment in the machines.

"Full-body scanners are used by dozens of countries around the world and are considered one of the most effective methods of screening," Merrifield said in a statement.

Sela testified it makes more sense to create a "trusted traveller" system so pre-approved low-risk passengers can move through an expedited screening process. That would leave more resources in the screening areas, where automatic sniffing technology would detect any explosive residue on a person or their baggage.

Behavioural profiling also must be used instead of random checks, he said.

"Having a random search at the airport is like Russian roulette," said SelaPolitical scientist Mark Salter, an aviation security expert at the University of Ottawa, testified alongside Sela. He told MPs he disagreed with Sela's take on full-body scanners, calling the machines a "genuine leap forward" because they not only detect current threats, such as liquid explosives, but also the next generation of non-metallic threats.

"It is a much better mousetrap," Salter said.