Abstract: The ultrasonic air data system determines the relative velocity of an aircraft with respect to the medium in one, two or three directions. In addition, it may determine the speed of sound and the approximate temperature. In the one direction system, a first ultrasonic transducer transmits a pulse to a second transducer where it is detected and reflected back to the first transducer and again reflected to the second transducer. The pulse transmit times for each direction are determined, and the relative velocity, the speed of sound and the approximate temperature are provided as a function of the transit time. In the two or three direction systems, three or four transducers are positioned in a two or three dimensional configuration. In the first half cycle, the first transducer transmits a pulse to the second where it is reflected to the third or last transducer in a two-dimension system and then to the last transducer in a three-dimension system.