Aerodynamically monitoring the performance of an aircraft's lifting surface provides the missing component in stall warning. The missing component is the ability to measure the premature loss of lift due to contamination such as insect deposits, snow, slush, or ice on the lifting surface. Conventional stall warning systems, which use a fuselage mounted angle of attack sensor, do not measure the actual stalling condition at the wing. The key to determining an early stall due to the presence of contamination is to measure the flow directly at the lifting surface. Local velocity changes in a region above the upper surface of the wing provide a consistent indication of an approaching aerodynamic stall even when contamination is present. This method of stall warning also offers new levels of safety during low level windshear recovery and takeoff performance monitoring.