ESDU 96037 introduces some of the fundamental concepts relating to the effects of structural flexibility for aeroplanes of classical configuration (aspect ratios greater than 4 and sweep angles less than 35 degrees) in wholly subsonic flow either in steady flight or in a quasi-steady pull-out manoeuvre. Bending and twist deformations of the wing and tailplane are assumed to occur only in the spanwise direction about a straight elastic or flexural axis; chordwise deformations are ignored. Weight distribution changes due to deformation are neglected. In trimmed level flight expressions are developed for aeroplane incidence, elevator angle to trim and elevator trim margin. The steady pull-out manoeuvre is treated as a quasi-steady perturbation superimposed on the steady level trimmed state and expressions are developed for aeroplane manoeuvre incidence, elevator manoeuvre angle and elevator manoeuvre margin. An elevator trim divergence speed is found to depend on tailplane torsional stiffness and pitching moment due to elevator deflection and is unchanged for manoeuvring flight. Finally, stability is considered in terms of overall static stability, constant speed static stability and overall structural mode static stability.