FedEx Corp (FDX.N), the world’s largest cargo firm, has signed a deal to buy 50 additional Boeing Co (BA.N) 767-300 freighters in the biggest order ever for the plane, allowing the aircraft maker to extend its production line well into the next decade. FedEx said the aircraft will be delivered by Boeing for its FedEx Express arm over the fiscal years 2018-2023. The latest deal brings FedEx’s firm orders for 767Fs to 106 and extends the company’s drive to modernize its fleet.