Selection by Air France-KLM Group of 50 Boeing 787-9 and Airbus A350-900 twinjets sets the scene for an interesting powerplant competition.
Air France-KLM is a loyal General Electric customer but the A350 is only available with the Rolls-Royce Trent XWB engine, meaning that the mainline carrier will be signing for its first Rolls-Royce engines in decades.
While GE's GEnx engine might appear the odds-on favourite for the 787 deal, Rolls-Royce said it will "absolutely" fight to take the powerplant contract for the type.
"We believe the Trent 1000 is a very strong [candidate]," the manufacturer added, indicating that the choice will be made by the end of the year, when the carrier group is due to finalise the order.
Air France-KLM's maintenance organisation has previously indicated that it would consider offering support for new-generation engines from Rolls-Royce as well as GE. Rolls-Royce said that this did not amount to a "sticking point".
KLM will be the first beneficiary of the long-haul order, becoming the operator of the 787-9 in 2016.
Air France will take its first A350 two years later, in 2018. But both carriers in the group will operate both aircraft types eventually, it said.
The order is aimed at replacing the 200- to 350-seat aircraft in the fleet over the medium term, said the group. While the firm orders are evenly split, 25 each, Airbus has listed 35 options against 25 for Boeing. The value of the firm portion is $12 billion at list prices.
Boeing Commercial Airplanes chief Jim Albaugh said the 787 would "bring outstanding value to the two airlines" and will be a "great complement" to their Boeing fleets.
Air France and KLM each operate Boeing 747 and 777 variants, while KLM also uses several 737 family members. KLM only operates the A330 from Airbus, while Air France essentially uses the whole Airbus family from the A318 to the A380.
By 2024 the Air France-KLM fleet will have 30 787s and 43 A350s. The company said the acquisitions are "scaled to a size that can be financed through cash flow generated from group operations".