A system and method for determining whether the relative rate of deployment of all the slats extending from a leading edge of an aircraft wing is the same as a predetermined relative rate of deployment. Each slat includes at least one slat deployment mechanism that includes a drive pinion drivingly coupled to each slat and a rotary actuator having an output shaft driven by a common input drive shaft. The system of the invention comprises a sensor associated with each rotary actuator to generate a signal indicative of the rate of rotation of the corresponding output shaft and to supply that signal to a controller. The controller is configured to analyze the signals supplied by the sensors and to generate an alarm signal if a relative rate of rotation of any of the output shafts differs from a predetermined relative rate of rotation.