By Agence France-Presse
The company said in a statement late Friday that it had agreed to buy 25 Boeing B787-9 aircraft, known as the Dreamliner, and 25 Airbus A350-900 aircraft.
In addition, it has the option to buy five more of each aircraft from both suppliers, meaning the eventual purchase could total 60 planes.
It said six would be delivered in 2019, 14 in 2020, 10 in 2021, 12 in 2022, 11 in 2023 and 7 in the year 2024.
A statement by Airbus indicated that the catalogue price of the 25 A350s alone would amount to $9.5 billion.
Turkish Airlines chief executive Ilker Ayci said that the announcement came after agreements signed during recent visits to France and the United States -- the homes of Airbus and Boeing -- by President Recep Tayyip Erdogan.
He hailed the deals as a "very important initiative to meet the need for wide-body aircraft at the new airport" and strengthen the fleet ahead of the 100th anniversary of the founding of modern Turkey in 2023.
"We believe this will not just accelerate the steady rise of Turkish Airlines, but also contribute to Turkish civil aviation as a whole," Ayci said, quoted by the Anadolu news agency.
The government plans to open the new airport by Istanbul's Black Sea coast on October 29, hoping to make it a global hub that can compete with Dubai for transfer traffic.
Turkish Airlines, which is 49-percent owned by the government through a wealth fund, has grown exponentially in recent years in a rise strongly supported by Erdogan to create a national champion.
Passenger numbers have swelled from just 14 million in 2005 to 69 million in 2017.
And the airline is targeting a total 74 million passengers in 2018 and wants to expand its fleet from 329 at present to 424 planes by 2023.