In recent years some types of aircraft have shown signs of structural trouble due to repeated loading and exploratory thought has therefore been given to the general problems arising. There are two main aspects to be considered: the nature and magnitude of the loads repeatedly occurring in flight and the behaviour and strength of aircraft structures under such loads. In this country a good deal of attention has already been given to the first side of the question, mainly by V-g recorder work, but also by some strain gauge investigations, but the other side of the matter—the resistance of aircraft structures to repeated loading— has so far received less attention. Direct experiments have not in this country gone much beyond exploratory work on a series of Typhoon tailplanes, described by Oaks and Townshend.