Bombardier’s CSeries plane will finally take to the skies again, possibly in the coming days, more than three months after it was grounded due to an engine fire.

The geared-turbofan engines, made by Pratt and Whitney, have been modified to adapt the oil lubrication system that led to the fire, with the first set installed in the second CSeries plane, known as flight test vehicle 2.

The plane came out of the hangar on Friday at the Mirabel airport, and officials will run a slew of tests before it takes off again.

The first plane, known as flight test vehicle 1, has had to undergo additional repairs, including some to the carbon-fibre wing that was damaged in the fire.

Rob Dewar, general manager of the CSeries program, said in a video on the company website that the engine modifications have had “no impact whatsoever to the performance,” including thrust, fuel burn, emissions and noise.

Spokesman Marc Duchense refused to specify a target date for a return to flying, saying only it will occur this month. That’s a change from the message of Bombardier officials including CEO Pierre Beaudoin, who have insisted since the May 29 fire that the plane would fly again “in the coming weeks.”

Even when the plane, touted as quieter and more fuel-efficient, returns to complete flight-test hours, many uncertainties remain for Bombardier’s CSeries development program, which has faced repeated delays and rising costs.

The biggest one will be whether entry into service could be pushed back, even though officials insist its target of the second half of 2015 remains unchanged despite the plane’s grounding.

RBC Capital Markets analyst Walter Spracklin said Friday in a note that the date likely had a six-month buffer, but with the latest delay, “this buffer is quickly being sopped up.”

Spracklin said if Bombardier does not have any additional development issues, the entry date could be achievable, but other issues could surface.

Earlier this week, Goldman Sachs analyst Noah Poponak downgraded Bombardier stock, saying a delay was “inevitable.”

The New York analyst anticipates the 110- to 160-seat plane will “negatively impact” Bombardier’s financial results and create “negative catalysts” for several years.

Poponak says Bombardier will not likely be able to dramatically pick up the pace of flight tests to about 160 hours per month, from 37 hours before the program was grounded, to meet its delivery deadline.

Uncertainty over the program prompted Swedish company Braathens Aviation to announce last week that it no longer wishes to be the first customer for the CS100 jets.

“We have informed Bombardier that we will not assume the role of formal launch operator of the aircraft type. Due to increased uncertainty, we are discussing possible changes to the aircraft delivery schedule with Bombardier,” Braathens said in a statement.

Bombardier’s Duchesne disputed any suggestion that Braathens’ decision is related to potential delays.

“They said they didn’t need the aircraft as early as expected,” Duchesne said. “Our point of view is they reviewed their business strategy. It’s not an issue for us.”

Dewar added that during the grounding, extensive testing and hardware and software upgrades were done, as well as maintenance checks that are usually done later in the program.

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Porter Airlines has placed a conditional order for the CSeries plane in hopes of expanding its flight network. However, Toronto city council voted to defer any decision on whether to permit jets at Toronto’s island airport until 2015.

The port authority has begun work on various studies including an environmental assessment, preliminary runway design and airport master plans, estimated at $3 million.

With files from Star’s wire services

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