FILE PHOTO: An Airbus logo is pictured during the delivery of the new Airbus A380 aircraft to Singapore Airlines at the French headquarters of aircraft company Airbus in Colomiers near Toulouse, France, December 13, 2017. REUTERS/Regis Duvignau

PARIS (Reuters) - European planemaker Airbus AIR.PA sealed on Thursday a formal order from AerCap AER.N for 50 Airbus A320neo planes, in a deal worth an estimated $5.4 billion at list prices.

The companies said in joint statements that AerCap had exercised an option to buy the 50 planes, with deliveries starting from 2022.

Airbus and Boeing BA.N are pairing with smaller regional rivals to add sales at the lower end of their $100 billion-a-year commercial plane duopoly, but the two market leaders are also laying the foundation for a longer-term strategic contest against more powerful threats such as China.

Deals with their smaller cousins may give Airbus and Boeing more options when they develop the successors to the best-selling Boeing 737 and Airbus A320, perhaps allowing them to offer a trio of large jets coupled to a pair of smaller ones.

Sources also told Reuters this week that Airbus was drawing up contingency plans to phase out production of the world’s largest jetliner, the A380 superjumbo, if it fails to win a key order from Dubai’s Emirates.