An unnamed European airline has signed a letter of intent (LOI) for 61 Bombardier CSeries aircraft. The agreement is for 31 firm orders and 30 options, Bombardier says.

“The LOI is subject to execution of a purchase agreement, which is expected before year-end,” the company says. The order could be worth as much as $2.4 billion dollars at list prices, and up to $4.8 billion if all options are exercised.

The order ends an 18-month sales drought for the CSeries since Delta Air Lines placed an order for 75 aircraft in 2016. Other than a 45-aircraft order from Air Canada, Bombardier has notched just a handful of orders for the CSeries since the Delta order.

The new deal is a shot in the arm for the once-beleaguered CSeries program, which was rescued last month by Airbus taking a majority stake in the program in a no-cash deal that stunned the industry. Airbus says it will assemble the aircraft for U.S. customers at in Mobile, Alabama, in a move that could resolve a decision by U.S. officials to subject it to U.S. tariffs if made by Bombardier in Canada. Boeing had complained, and the U.S. Commerce Dept.’ agreed, that Bombardier had been pricing the aircraft way below the cost of production.

After the deal closes, Airbus will own 50.01% of the CSeries program; Bombardier will hold 31%; and the government of Quebec, which had invested $1 billion in the program in 2015, will have a 19% stake.

Bombardier has warned customers that CSeries deliveries this year could slip to 20-22 aircraft, down from an expected 30-35, due to production ramp-up issues for Pratt & Whitney’s PW1500G geared turbofan engine. Pratt will make cash advances to Bombardier to support excess CSeries inventory and is working with the airframer to reschedule deliveries. The production slip could reduce revenues at Bombardier’s commercial aircraft unit by $300-500 million.

The Airbus deal could benefit the CSeries program by bringing the European airframer’s clout to bear on the supply chain. Some analysts believe supply-chain costs could drop 30-40% thanks to Airbus’ muscle. JP Morgan believes that decreasing procurement costs by 10% would add six points to the program margin.

Not including the newest order, Bombardier has 360 firm orders for the CSeries, with a backlog, mostly for the larger CS300 variant, and a backlog of 341 aircraft, according to the company’s website.