An order for 39 new Boeing aircraft worth $13.8 billion has been signed by Singapore Airlines.

The airline has agreed to place firm orders for 20 Boeing 777-9s and 19 Boeing 787-10 Dreamliners, for additional growth and fleet modernisation throughout the next decade.

Six options of each aircraft type will increase the order to 51 aircraft if confirmed.

The 777-9s are due for delivery from the 2021-22 financial year and the 787-10s for delivery from the 2020-21 financial year.

The deal gives SIA flexibility to substitute the 787-10 orders for other variants of the 787 family.

The airline is already the launch customer for the 787-10, which is currently in development, having placed an initial order in 2013 for 30 aircraft for delivery from the 2018-19 financial year.

SIA has outstanding orders with Airbus for five A380-800 superjumbos and 57 A350-900s.

Wholly-owned SilkAir has outstanding orders with Boeing for 37 737 MAX 8s, while Scoot has orders for eight 787-8/9s and Tigerair has orders with Airbus for 39 A320neos.

SIA is a longstanding Boeing customer with more than 50 current generation long range 777s in service.

Subsidiaries SilkAir, Scoot and SIA Cargo are also operators of Boeing aircraft, with 737-800s, 787-8/9s and 747-400 Freighters in service, respectively.

SIA chief executive, Goh Choon Phong, said: “Today’s major order for widebody aircraft enables us to continue operating a modern and fuel-efficient fleet, providing the SIA Group with additional expansion opportunities to ensure that we retain our industry-leading position.

“We are continuing to invest for the future of the SIA Group. This order is also another demonstration of our commitment to further growing the Singapore hub, as we will be able to offer even more travel options for our customers.”