FedEx Express, FedEx Corp.'s air and international unit, said it will purchase 19 Boeing 767 freighters as part of FedEx's plan to modernize its domestic U.S. air fleet.

The 19 Boeing 767s will be delivered from fiscal years 2015 to 2019 and will replace older Boeing MD-10 and Airbus Industrie A-310-200 aircraft, FedEx said. The 767s will provide similar capacity as the MD-10s, which are retrofitted McDonnell Douglas DC-10s, but with an approximate 30-percent increase in fuel efficiency and a 20-percent reduction in unit operating costs, FedEx said.

The announcement, made Friday, comes less than a month after Memphis-based FedEx announced the permanent retirement of 18 A310 aircraft and 26 related engines as well as six MD-10 aircraft and 17 related engines. With that decision, FedEx brought the total number of aircraft that it planned to retire by the end of its 2013 fiscal year to 50.