ESDU 03011 introduces lateral static aeroelasticity in which the effects of structural deformation on lateral stability, controllability and loading in steady lateral manoeuvres are considered. The effect of deformations are quantified using the concept of modified derivatives in which the stability derivatives associated with rigid aeroplane stability and controllability are changed to incorporate deformation effects, assuming all dynamic effects can be neglected. The modified derivatives are derived in qualitative terms to illustrate their behaviour, and the important roles of divergence speeds and reversal speeds are identified. The analysis of this Item is in line with the approach of Item 96037, which provided a qualitative introduction to longitudinal aeroelasticity, where the effects of symmetric deformations on longitudinal controllability, quasi-static loads, static stability, trim characteristics and quasi-steady pull-out manoeuvres of both swept and unswept configurations are described. In this Item, like the previous Item, consideration is given to what happens when deformation, relative to a reference state, of the various components, wing, tailplane, fin, fuselage and engine nacelles and pylons, but now the deformations are antisymmetric, giving rise to changes in lateral stability and controllability and in the antisymmetric loading distributions. The effects of structural flexibility on the lateral stability characteristics are assessed by noting the changes in the approximations for static stability, spiral mode, rolling subsidence and Dutch roll in terms of the lateral stability derivatives when modified derivatives are used.