Airbus has agreed to buy a majority stake in Bombardier’s CSeries jetliner programme, giving a powerful boost to the Canadian plane- and train-maker in its costly trade dispute with Boeing.

The deal, which would come at no cost for Europe’s largest aerospace group, would give Airbus a 50.01 per cent interest in CSeries Aircraft Limited Partnership, which manufactures and sells the jets, the companies said.

While Bombardier will lose control of a plane programme developed at a cost of $6bn (£4.5bn), it gives the CSeries improved economies of scale, a better sales network and, crucially, could change the power balance in the trade dispute with Boeing.

The 110-to-130 seat plane, which has not secured a new order in 18 months and is being threatened by a possible 300 per cent duty on US imports, would be built for US airlines at Airbus’s Alabama assembly plant, circumventing any import penalties in a move that apparently caught Boeing off guard.

Bombardier said the partnership should more than double the value of the CSeries program.

“Bombardier no longer has control of this jet, but then again, it’s better to have a 30 per cent share of a very successful programme than to struggle with a highly risky programme that was perhaps too big for them from the start,” said aerospace analyst Richard Aboulafia.

Canadian innovation minister Navdeep Bains, who must decide whether to approve the deal, said in a statement that “on the surface, Bombardier’s new proposed partnership ... would help position the CSeries for success”.

Boeing – which is also locked in a separate 13-year trade dispute with Airbus – said it was a “questionable deal” between two of its subsidised competitors.

At 08:15 on Tuesday morning, Airbus shares were up 2.5 per cent at €78.96, the biggest rise by a European blue-chip stock.

Airbus chief executive Tom Enders said the company, based in Toulouse, France, had offered to assemble some of the narrowbody jets at its US plant in Alabama for orders by US carriers.

The US assembly line would mean the jets would not be subject to possible US anti-subsidy and anti-dumping duties of 300 per cent, Bombardier chief executive Alain Bellemare said.

Mr Bellemare called the deal with Airbus, which was first attempted unsuccessfully in 2015, a “strategic” decision that is expected to close in the second half of 2018.

“We’re doing this deal here not because of this Boeing petition. We are doing this deal because it is the right strategic move for Bombardier,” Mr Bellemare said, referring to Boeing’s complaint that the Canadian firm received illegal subsidies and dumped CSeries planes at “absurdly low” prices.

A Boeing spokesman dismissed the agreement as a “questionable deal between two state-subsidised competitors” to try to skirt a recent US trade finding against the CSeries.

In February, the Canadian government announced C$372.5m ($297m) in repayable loans for the CSeries and another Bombardier jet programme.

The Airbus investment does not place any more financial burdens on Ottawa, two sources close to the case said on Monday.

The sources, who requested anonymity because they were not authorised to speak to media, also said the deal would have no effect on a separate dispute between Canada and Boeing over a proposed purchase of 18 Super Hornet jets.

Ottawa has frozen contacts with Boeing’s military wing until the company drops its challenge against the CSeries.

Bombardier said the deal would not result in job losses and would keep the head office in Montreal. Unions said the deal would benefit the programme.

“Ultimately, the US actions have created a stronger Bombardier,” said Jerry Dias, president of Unifor, which represents some of Bombardier’s unionised workers in Canada.

The Boeing-Bombardier dispute has snowballed into a bigger multilateral trade dispute, with Prime Minister Theresa May asking US President Donald Trump to intervene in order to save British jobs.

Bombardier is the largest manufacturing employer in Northern Ireland. Ms May’s Conservatives are dependent on the support of the Democratic Unionist Party party for their majority in Parliament.

Business Secretary Greg Clark welcomed the Airbus deal with Bombardier, saying Britain would work closely with the firms to protect its interests and the leader of the Northern Irish party propping up Ms May’s minority government said it was “incredibly significant news” for Belfast.

Talks for the deal between Airbus and Bombardier first started in August. Enders said the deal was different from an earlier round of talks in 2015, when he abruptly ordered an end to negotiations. He said the CSeries has since been certified, entered service and was performing well.

“It’s an entirely different situation,” he said.

Delta Air Lines, which ordered 75 CSeries planes, said after the announcement that it looked forward to introducing the planes into its fleet.

The deal could also drive Boeing closer together with Brazil’s Embraer, with which it already cooperates. Embraer’s E2 jet is one of the main potential losers from the CSeries deal.

“The world has two top-tier airframers, and two second-tier airframers,” said Teal Group analyst Richard Aboulafia. “Airbus and Bombardier are now allies. This greatly increases the likelihood of a stronger Boeing-Embraer alliance as a response.”

Under the deal, Bombardier will own about 31 per cent, while Investissement Québec, the investment arm of the province of Quebec, will hold 19 pe rcent. In 2015, Quebec took a 49 per cent stake in the CSeries programme for $1bn, although its stake was more recently diluted to 38 per cent.

Quebec’s largest pension fund, which holds a 30 per cent stake in Bombardier’s rail division, said the decision strengthened the company and improved its growth prospects.

Bombardier is in the middle of a five-year turnaround plan after considering bankruptcy because of a cash-crunch as it developed multiple plane programmes simultaneously, including the CSeries.

The deal also provides Airbus warrants exercisable to acquire up to 100 million Class B Shares of Bombardier.

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Airbus will provide procurement, sales and marketing, and customer support expertise to CSALP, the companies said.

There will be no cash contribution by any of the partners, nor will CSALP assume any financial debt, they added.