In airborne radomes a considerable effort has been devoted to the calculation of boresight errors but little attention has been given to the computation of flashlobes. These are caused by reflections from the radome wall and generally appear at angles well away from the boresight of the enclosed antenna. In certain circumstances they can seriously compromise the sidelobe suppression of the overall system. This paper describes an efficient method for flashlobe prediction which gives more detailed information and can be used in an optimisation of radome shape and wall build. The technique is based on the subaperture method which has already been successfully used to predict other bulk radome effects.