trijet

A trijet, or three-jet aircraft, is a jet-powered airplane that uses three jet engines.

The most common configuration places two engines under the wings and a third engine in a tail-mounted pod on the rear fuselage. This layout was widely used on several early wide-body airliners and was chosen to provide needed power and redundancy with the engine technology available at the time.

The tri-jet concept emerged in the 1960s and 1970s as a compromise between range, payload, and the reliability of available engines before twinjet designs with extended ETOPS capability became practical. Its main advantage was continued operation after a single engine failure, but this came at the cost of higher maintenance, greater weight, and more drag.

Notable examples include the Lockheed L-1011 TriStar, the McDonnell Douglas DC-10, and the MD-11. In the Soviet Union, the Tupolev Tu-154 served a similar role as a three-engine airliner. Over time, many trijets were retired or converted to freight aircraft as twin-engine efficiency improved and long-range ETOPS coverage expanded.

Today, tri-jet airliners are relatively rare in passenger service. The remaining occurrences are primarily cargo aircraft or older models phased out of most commercial fleets. The term remains of historical interest in civil aviation discussions of aircraft design and performance trade-offs.