The effect of a turbulent, free shear layer is to introduce a random phase variation on a light beam propagating through that layer. It an incoming parallel beam is brought to focus after propagating through the layer, then the effect of this added random phase variation is to scatter energy out of a diffraction limited focused spot and form a halo around the spot. In an imaging system, this could degrade image quality and reduce contrast due to scattering of energy over a large area. The rapid growth of a free shear layer results in a phase screen whose characteristics rapidly change with distance in the flow direction, therefore part of the beam may propagate through a benign region of the flow field, while that part of the beam located further downstream may be severely aberrated. The specific flow condition chosen is one in which the flow separates from a cylindrical turret with a large optical aperture. The spatially varying characteristics of a free shear layer are explicitly accounted for by constructing a spatially varying phase screen, in which the aerodynamic characteristics are based on turbulence measurements made on large scale wind tunnel models, and on flight measurements made on a large aircraft. The resultance Strehl ratios and beam profiles for typical flight conditions are presented.