Aerospace giant Bombardier has won a contract with American Airlines worth a potential £1bn for 30 regional jets which are part-made in Belfast.
The $1.4bn deal is the latest good news for the Canadian firm's Northern Ireland workforce of around 4,500 after it won a US legal challenge by rival Boeing over a separate order for its C Series jets.
The complete centre fuselage for the CRJ900 is manufactured in Belfast.
American Airlines has placed a firm order for 15 of the planes with the option to buy 15 more.
Bombardier said the firm deal was worth $719m (£528.9m).
East Belfast DUP MP Gavin Robinson said the order was a huge boost for the company and its Belfast plant.
"Whilst the focus has been mainly on the more recent C-Series planes it is important to recognise the other aircraft which are still being manufactured and sold," he said.
"These all contribute to the success of the company.
"There have been a number of recent orders secured by Bombardier and I hope this is a sign of things to come."
The deal was announced as Bombardier revealed a 12% increase in revenues for the start of 2018 to $4bn.
Fred Cromer, president, Bombardier Commercial Aircraft, said: "We are pleased with American's continued confidence in Bombardier and the CRJ900 aircraft.
"This order is a testament to the tremendous value that the CRJ Series provides to airlines in the North American regional market."
Bombardier's first quarter results also revealed that a tie-in with rival Airbus is expected to be signed before the end of June, ahead of schedule.
The companies announced a deal last year for a joint venture for the production of the C Series, a narrow-bodied passenger jet.
Its wings are made in Belfast - and under the proposed deal, the complete jet will be assembled at a new Airbus plant in Alabama in the US.
Alain Bellemare, president and chief executive of Bombardier, said: "We continue to deliver on our financial commitments and make solid progress executing our growth programmes and strategic initiatives."
The CRJ900 deal was welcomed by Sinn Fein councillor Mairead O'Donnell, chair of Belfast City Council's growth and regeneration committee.
She said: "Bombardier is a huge employer here and is a massive part of our economy, so today's news that they have secured a $719m deal to sell up to 30 of its CRJ900 jets to American Airlines will be welcomed by many in Belfast and across the north."
Last year Boeing had complained about Bombardier selling its C Series jets to Delta Airlines below cost price.
The US Department of Commerce recommended a near 300% punitive duty on sales of the jets for five years, putting around 1,000 jobs in Belfast at risk. But the International Trade Commission (ITC) in the US ruled against Boeing and in favour of Bombardier in January.