THE Trident has been designed with the objective of achieving freedom from fatigue cracks on the primary structure, during the operational life of the aircraft. Additionally, in areas where the fail safe concept can be applied, the design aim has been to provide multiple load paths and/or crack stoppers so that, in the event of any one member failing, the remaining structure can sustain at least limit loads for a longer period than the interval specified between major inspections of the structure. In the places where it is not possible to apply the fail safe concept, that is on flap and slat tracks, tailplane hinge fitting, engine mountings and landing gear, a substantial margin of safe life is provided.