UAL Corp.’s (UAUA) United Airlines finalized its order to buy 25 of Boeing Co.’s (BA) 787 Dreamliners with an option to buy another 50.

United, the third-largest U.S. airline by traffic, hadn’t ordered new aircraft for 11 years. In December, United unveiled plans to order an equal number of planes from Boeing and rival Airbus, a subsidiary of European Aeronautic Defence & Space Co. (EAD.FR, EADSY).

The Boeing order is valued at $4.2 billion at average list prices, but airlines often pay less when placing big orders. The planes should be delivered just as United begins to retire is Boeing 747 and 767 models flying internationally.

The Dreamliner was plagued by costly delays for years, but it finally made its first flight in December. Boeing’s commercial aerospace division also suffered from a drop in demand as airlines quit ordering planes during the recession and the subsequent plunge in travel demand.

But in the fourth quarter, United Airlines noted a strong recovery in international passenger traffic, especially on transatlantic routes, as it posted a narrower loss. The Dreamliner, thanks to improved fuel efficiency, will allow airlines like United to add new, nonstop city routes.