A trijet is an aircraft powered by three jet engines. Early twin-jet 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.

TRIJET AIRCRAFT
Aerojet unveils trijet for reusable hypersonic power
Twin-jet and trijet aircraft: a study for an optimal design of regional aircraft
H ∞ longitudinal control of crippled trijet aircraft with throttles only ☆
Boom time : stretched, trijet 50-seat configuration to be tested by subscale supersonic demonstrator
Searches for Low-Mass Dijet Resonances in Trijet Final States using Monte Carlo Samples
Falcon 8X : Dassault's flagship trijet delivers more range, comfort and capability than ever before
Integration and Vehicle Performance Assessment of the Aerojet "TriJet"Combined-Cycle Engine
Dassault's new Falcon 8X airborne : ultra-long range trijet on track for second half 2016 service entry
Integration and Vehicle Performance Assessment of the Aerojet "TriJet"Combined-Cycle Engine - 16th AIAA/DLR/DGLR International Spac...