A trijet is a jet aircraft powered by three jet engines. Early twinjet designs were limited by the FAA's 60-minute rule, whereby the flight path of twin-engine jetliners was restricted to within 60 minutes' flying time from a suitable airport, in case of engine failure. In 1964, this rule was lifted for trijet designs, as they had a greater safety margin. This led to a flurry of trijet designs, which in their heyday of the 1980s were the most popular airliner configuration. However, subsequent improvements in engine reliability and a corresponding relaxation in airline safety rules made the trijet obsolete for normal passenger services, and no manufacturer now produces three-engine airliners.