Boeing’s slow-selling 747-8 received a huge boost Thursday with a firm order for 14 freighter versions of the big quadjets from UPS. The contract, which includes options for 14 more 747-8Fs, raises the program’s order backlog from 15 to 29 and potentially extends the type’s production run for more than another two years at the current rate. Boeing now builds six 747-8s per year.

Schedules call for delivery of the 14 new aircraft between 2017 and 2020. UPS said the 747-8s will allow it to begin a “cascade” of aircraft route reassignments meant to add capacity to the company’s busiest lanes, optimizing cargo volume beyond the effect of adding new jets.

“UPS is making several strategic capital investments for increased global operating capacity,” said UPS chairman and CEO David Abney. “These investments will help enable customers to expand their presence in new and existing markets while fueling our profitable growth and attainment of UPS’s long term business objectives.”

UPS added that the 747-8 offers training and operating efficiencies because pilots of the company’s existing 747-400 fleet will enjoy a common equipment rating, allowing them to fly both aircraft types.

It also stressed the greater economies of scale in maintenance and ground handling the airplanes will bring. The 747-8 freighter carries 34 shipping containers on its main deck and 14 in its lower compartments. It holds a cargo capacity of 307,600 pounds, or approximately 30,000 packages, and flies to a range of 4,340 nautical miles.

“UPS could not have selected a better aircraft to meet its growing business needs,” said Boeing Commercial Airplanes vice president of sales for North America and leasing Brad McMullen. “We’ve continued to make the 747-8 Freighter even better, and we look forward to seeing UPS introduce it to its fleet.”