This order, previously attributed to an unidentified customer, follows Swiss' 2013 order for six 777-300ERs, and will form the backbone of the Swiss flag-carrier's long-haul fleet renewal.

"I am delighted that with the formal signing of the contract, Swiss has set a further milestone in its long-haul fleet renewal," said Harry Hohmeister, CEO of Swiss.

"Swiss' latest order for additional airplanes is a testament to the unrivalled economics of the 777-300ER as the carrier continues to renew its long-haul fleet," said Todd Nelp, vice president of European Sales, Boeing Commercial Airplanes. "The 777-300ER will help Swiss to offer customers good service and maintain its position in international travel."