Costs for the used F-18 fighter jets the government plans to purchase from Australia are still up in the air, the minister of defence revealed Tuesday when pried by opposition MPs on the topic.

“We don’t have the exact costs just yet,” Harjit Sajjan told members of the House Standing Committee on National Defence.

“We will know, but we want to make sure we have the right details. Giving you an estimated cost right now would be irresponsible. It’s better to make sure that we get you the correct information once we have the further details,” he said.

The government first announced that it would be buying 18 used Boeing F-18s from the Australian government for roughly $500 million. In the Royal Canadian Air Force the model is known as the CF-18. Canadian fighters have flown the jets since 1982. Canada opted out of a plan to purchase a fleet of modern Boeing F/A-18 Super Hornets from the United States and into an agreement with Australia for the more than 30-year-old planes in December.

The defence minister said the first of the planes purchased from Australia should touch down on Canadian soil in Spring 2019.

Which specific Australian F-18s to be sold to Canada has yet to be settled.

“We don’t want to take aircrafts that are at the very end of their service life,” Patrick Finn, assistant deputy minister of materiel of the Department of National Defence, told the committee. “These will be flyable assets that are in service with the Royal Australian Air Force as we see today.”

Finn said the planes that Canada is purchasing have been used more on average than the same jets currently in Canada’s air force. He asked for the committee to look beyond the hours-used of the aircraft.

“They, like us, have put a lot of investment into those air craft. I’ve sailed on 40-year-old ships that had brand new modern missiles. I think we’ve got to be careful about the age of an aircraft and saying that reflects its capability,” Finn said.

Finn said the bill of sale has not yet been signed for the jets and the acquisition is currently being reviewed by a third party. He added Canada has been given data about each of the airplanes in question and has been able to conduct their own examinations of each.

“We know exactly what shape they’re in,” Finn said. “We actually expanded that further and we have inspection points — very discreet ones — where we actually put the aircraft through a very detailed maintenance process.”

If Canada is offered an aircraft in better shape a few months later than one that can be acquired immediately, then it will choose to wait for the better model, Finn said.

Canada plans to fly the fleet of F-18 fighter jets until 2032, after which it plans to adopt the plane’s successor.