. Optimal design of complex engineering systems, such as aircraft composite
structures, can often be accomplished only by decomposition techniques. In general, it is
characterized by a multidisciplinary task, usually involving multiple objectives, with many
design variables and several constraints associated to each one of the disciplines taken
into account. One of these techniques is represented by the multilevel approach, where
the complex problem of multidisciplinary optimization is solved based on the idea \divide
and conquer". The original problem is split into several smaller subproblems, making the
new conguration inherently suited to parallel and distributed computing. In this paper the
optimal design of a composite wing-box is addressed by using a parallel two-level scheme,
where a stochastic method is used to solve each second-level problem. At this level, since
the changes in the components of one of the sub-problems have no in°uence on the solution
of the thers, they can be solved simultaneously
