The federal cabinet is poised to consider the possible deployment of CF-18 jetfighters and CP-140 Aurora surveillance aircraft in the ever-expanding air war against the Islamic State of Iraq and the Levant.

But there is concern within National Defence and among critics about the wear and tear of yet another combat mission on the venerable fighter-bombers, which are well into middle age, and about how the aircraft will be used.

The expectation that Canada will contribute a combat detachment is running high in the international community, as allies have already offered specific airfield space in the region.

Before that happens, though, the Harper government has promised to hold a vote in Parliament — a pledge Foreign Affairs Minister John Baird repeated Monday.

"We have been asked to do more by the Obama administration," Baird told the House of Commons under questioning by the NDP. "I can assure the member opposite, clearly no decisions have been taken."

He went on to state that "if there were to be a combat mission, we would seek to bring it before Parliament as a matter of confidence."

Beyond the initial airstrikes?

Declaring the vote to be a matter of confidence, which if lost could technically defeat the government, smacks more of pre-election bravado than political drama, since the Conservatives have more than enough votes to carry the motion.

But it is also a sign of how deeply invested the Harper government sees itself in the struggle against the Islamic extremists who captured the world's attention with a series of atrocities in northern Iraq and Syria, as well as the savage beheadings of two captured American journalists and a British aid worker.

Skeptics, including a former air force officer, wonder how much more can be accomplished from the air beyond the initial strikes carried out over the last week by the U.S. and a host of Arab allies.

"The element of surprise is gone," said retired colonel Paul Maillet, who noted that ISIL has already stated publicly that it will disperse its headquarters and other administrative operations.

"Now, in this kind of campaign, I believe you are almost past the utility of using the air force. They should pause and let the Iraqi army do its thing."

He does see the need for aircraft to support local forces when called upon, but there are already a number of countries contributing jets.

A further series of precision strikes on infrastructure targets like bridges and power plants would only add to the misery of people under ISIL occupation, said Maillet, a former air force engineer and now defence analyst.

"What they have done is taken out all of the high-value, easy targets now," he said. "What they're going to be doing is going after very difficult targets that are going to hide themselves in buildings in populated areas. The leadership (of ISIL) is going to be incredibly hard to dig out the cities without causing civilian casualties."

Concerns over aging fleet

The air force has four CF-18s already in the field flying air policing missions over the Baltic as part of NATO's eastern European reassurance measures.

There is concern about the impact of deploying the aging fleet even further.

In terms of a jet's airframe life, every hour spent on combat sorties equals three regular missions at home, and the CF-18s have already used up about 73 per cent of their lifespan, according to documents laid before Parliament in 2012.

Following the Libya bombing campaign of 2011, there was concern in the air force that despite life extension upgrades under the former Liberal government, the fighters were being driven too hard.

Each aircraft has about 8,000 hours of airframe life before major structural extensions are needed.

Maillet said he's not as worried as much about the physical condition of the aircraft as he is about the effect another mission will have on the entire fleet's support structure.

Combat operations have a tendency to chew through spare parts, which could prompt the air force to curtail other activities — and possibly cannibalize other jets — to keep the front line going, he said.

Internal defence documents support that assessment, noting in 2012 that on future missions a "permanent surge" in fighter operations could be "sustained indefinitely, if accompanied by a reduction in support to other users" — meaning domestic operations such as Norad and other routine missions involving the navy and army.