An Examination of the available data on aircraft unreliability, whether on civil or military aircraft shows quite clearly that the systems engineering is more troublesome than the structural engineering.

The statistics show that landing gear, brakes, hydraulics, fuel and air conditioning systems are all at fault to approximately the same degree. In addition equipments for which the airframe manufacturer is not directly responsible, are a frequent cause of trouble.

The aircraft manufacturers’ contribution to improving reliability must come from three directions.