Irish budget carrier Ryanair has agreed to acquire 175 new Boeing 737-800s, an agreement it values at nearly $15.6 billion at list prices.
The carrier says the deal, yet to be finalised, will take its fleet to more than 400 aircraft by the "end of the delivery stream" in 2018.
Once approved by Ryanair shareholders the purchase will, the airline claims, be the "largest ever" aircraft order by a European carrier.
The 737-800s are exclusively powered by CFM International CFM56 engines.
Some 75 of the new aircraft will replace part of Ryanair's current fleet of 305 737s. "But the remainder will drive new growth of Ryanair's fleet of young, highly efficient aircraft," the carrier says.
Ryanair says it is continuing to evaluate the re-engined 737 Max, which is due to enter service in 2017.