Trijets are more efficient and cheaper than four-engine aircraft, as the engines are the most expensive part of the plane and having more engines consumes more fuel, particularly if quadjets and trijets share engines of similar power, making the trijet configuration more suited to a mid-size airliner compared to larger ...

Many FedEx planes, specifically the McDonnell Douglas MD-11 and MD-10, feature three engines (a "trijet" configuration) because of their historical advantage in range and payload during the late 20th century. When these planes were built, international regulations (ETOPS) restricted twin-engine planes from flying long distances over oceans, making three-engine planes the perfect "middle ground" between smaller twin-jets and massive four-engine 747s. While most passenger airlines retired trijets in favor of more fuel-efficient twin-engine planes (like the 777 or A350), cargo carriers like FedEx find them exceptionally valuable because they have a high weight-carrying capacity and are already paid for, making the "cost per ton" very competitive for freight. As of early 2026, FedEx is one of the last major operators of the MD-11 freighter, though they are gradually phasing them out in favor of the twin-engine Boeing 767 and 777 freighters to meet newer environmental and fuel-efficiency standards. The iconic third engine, mounted at the base of the tail fin, remains a symbol of the heavy-lift "workhorse" era of global logistics.