Singapore Airlines has formally confirmed its order for 20 Boeing 777-9s and 19 787-10s. The order is theoretically worth $13.8bn at current list prices. The airline also has options for 12 additional aircraft, six of each aircraft type.

The signing ceremony, which took place at the White House, was witnessed by U.S. President Donald Trump and Prime Minister of Singapore Lee Hsien Loong, along with Singapore Airlines' CEO Goh Choon Phong and Boeing Commercial Airplanes' President & CEO Kevin McAllister.

The aircraft — until now attributed to an unidentified customer — were already included in the Boeing order book. Commitments for both aircraft models were announced in February.

Singapore Airlines already has more than 50 777s in service and is the launch customer of the 787-10, the first of which is scheduled for delivery in the first half of 2018. With a prior order for 30 787-10s, the airline now has 49 on order, making it the largest customer for this type.

The 787-10 will serve the airline's medium-range operations while partnering with the 777-9 for long-haul routes.

The Singapore orders mark the end of a two-year order drought for the two Boeing long-range twins. The 787-10 had not booked an order since November 2015 (18 aircraft for EVA Air), while the last 777X order was received in June 2015 (30 aircraft for unidentified customers, including the 20 for Singapore Airlines).

Boeing recently kicked off wing production for the first 777X, which is scheduled to roll out in 2018.