The sound pressures, associated with a jet efflux, set up stresses in an aircraft structure which are essentially those occurring in the resonant condition of the structure. These sound pressures contain components in a wide range of frequencies and the resultant stresses in the structure have low magnitude by normal structural standards but, because of the high frequency, they are very important from the fatigue standpoint. A rigorous theoretical approach is being developed at Southampton University which, although extremely difficult to apply to actual aircraft structures, emphasises the factors which must be considered. However, for immediate practical use it is suggested that an approximation can be made to render the problem tractable. It is considered that in an actual aircraft the effects are primarily local and on this assumption an approximation is developed and compared with test results. Reference is made specifically to the de Havilland Comet aircraft.