We study nonlinear deformation and bearing ability of a composite panel of grid structure that used as a bearing element of a caisson of an aircraft wing. The panel is loaded by bending moments and shearing force. We solve the problem in displacements using one-term approximation of the function of flexure. We determine the least eigenvalues and the limiting values of stresses for fiber-glass plastic panels of various types of grid structure when they deform jointly with longerons of a caisson. We propose a rational structure of supporting ribs for a grid composite panel.