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The most recent need to update airplane gust load design requirements became apparent in the late 1980's as new aircraft designs evolved whose active control systems depended on better descriptions of design level atmospheric gusts. As a result, the various national certifying agencies began to require various new and different, but often overlapping, gust load design analyses for certification and delivery of new airplane models. This led to recent efforts by the manufacturers and the certifying agencies to harmonize the various national requirements; which, in turn, required a redefinition of atmospheric disturbances or gusts. The past and continued evolution and development of airplane gust loads design requirements is discussed and is shown to depends on the definition and characterization of gust structure, accurate aircraft response analysis, and good gust encounter and aircraft operations statistics.

The Boeing program to investigate methods for establishing fatigue curves for broad band random loading is described. The approach used was to absorb the trends indicated by the results of the experimental program, together with the results of other investigations, into an expression involving the constant cycle S-N relationship, the root mean square stress, and other simple parameters which could be derived from the random load stress power spectrum and from the appropriate stress frequency distributions.