Bombardier has won a $5.6bn (£3.84bn) order for its C Series passenger planes from American airline Delta.
It has placed a firm order for 75 of the aircraft, with an option for 50 more.
Bombardier described the deal as a “watershed moment”, after orders had stalled for two years.
Wings for the aircraft are manufactured in Belfast. In February, the firm announced 1,080 job losses at its five Northern Ireland plants.
It said cost over-runs and delays to the C Series project were a major factor.
Earlier this month, the firm adjusted its job cuts programme in Belfast, announcing a greater number of redundancies in 2016.
The latest order is the largest in the history of the Canadian-owned aerospace firm.
Confirmation of the Delta order will lift two years plus of gloom surrounding the C Series.
This is a symbolic win over Boeing and Airbus.
It will provide a much-needed fillip for the project and help steady the Bombardier business.
Unions in Belfast will ask what it means for jobs.
Bombardier has already begun trimming its local workforce by a planned 630 this year.
Unless anything changes, there would be a further 450 redundancies in 2017.
No clarity is likely on that in the immediate future.
But workers will be heaving a sigh of relief at the news – boosting morale as well as company finances.
Alain Bellemare, chief-executive officer of Bombardier, said the news of a new order of C Series planes showed the company’s “turnaround plan” was gaining traction.
“Our decisive actions to improve our operations and business model across all our businesses are starting to pay off.”
Michael Ryan, vice-president and general manager at Bombardier Belfast, said: “We’re delighted that another customer has placed such a significant order for the C Series aircraft.
“This is a further endorsement of the aircraft’s excellent operating economics and environmental credentials, to which we in Belfast are contributing with the production of the advanced composite wings.”
Initially, Delta is taking the smaller CS100 model of the plane.
The company has been under severe financial pressure as cost overruns on its new C Series jet have drained cash out of the company.
The C Series programme received $1bn (almost £700m) from the provincial government in Quebec last year.
The firm has also been hit by a downturn in the business jet market.
Bombardier is the largest manufacturing employer in Northern Ireland and supports hundreds more jobs through its supply chains.
More than half of the jobs being cut this year come from the firm’s “complementary labour force”.
That part of the workforce is made up of temporary and contract workers and tends to fluctuate depending on demand.
Late last year the Northern Ireland workforce was asked to accept pay cuts and other changes to terms and conditions with the firm saying it was “in serious financial crisis”.
However the proposal was overwhelmingly rejected in a ballot of union members.