Abstract: A specially contoured barrier type filter disposed in front of a helicopter turbine inlet provides for maximized airflow during forward, as well as sideways flight. The contouring additionally reduces the tendency of the filter to clog. A bypass mechanism is provided should the pressure differential across the filter exceed a predetermined value. The bypass configuration achieves a limited particle separation function in order to provide residual protection. An air box attached to the inlet is formed to provide low distortion levels in the airflow entering the engine inlet.