The new airplanes, Boeing's 767 and 777 freighters, have a list price of $6.6 billion, said Boeing, which has sold more than 50 widebody freighters so far this year, including the latest order.

Air freight demand is expected to increase 4 percent this year, according to the International Air Transport Association (IATA). Last year was the best for cargo since 2010, with traffic growth more than doubling to 9 percent, three times the growth in capacity.

While trade tensions are rising, the industry is counting on e-commerce continuing to soar, with more people buying products online for quick delivery.

FedEx's order comes nearly four months after rival United Parcel Service Inc said it had ordered 14 additional Boeing 747-8 cargo jets.

(Reporting by Arunima Banerjee in Bengaluru; Editing by Cynthia Osterman)