The term “All-Weather Systems for Helicopters” is capable of many different interpretations dependent upon operational requirements. Certainly there are no hard and fast rules laid down defining the equipment required to enable a helicopter to operate under adverse weather conditions. The accuracy to which the aircraft has to be flown under instrument conditions and the ability of the pilot to complete a given mission safely without undue fatigue are the prime considerations which need to be considered in determining the facilities and degree of sophistication necessary for a flight control system.