An aircraft freestream data system, comprising: a first ultrasonic air data system, UADS, configured to sense local acoustic properties at a first location on one side of an aircraft; a first local air data module operatively connected to the first UADS and configured to determine first local air data of the first location and to output first local air data parameters including first local airspeed, first local wind angle, first local speed of sound, first local air temperature and first local Mach number; a second UADS configured to sense local acoustic properties at a second location on a second side of the aircraft, opposite the first side; and a second local air data module operatively connected to the second UADS and configured to determine second local air data of the second location and to output second local air data parameters including second local airspeed, second local wind angle, second local speed of sound, second local air temperature and second local Mach number; and a freestream data module operatively connected to the first local air data module and the second local air data module, and configured to: receive the first local air data parameters from the first local air data module; receive the second local air data parameters from the second local air data module; determine one or more freestream air data parameters based on converting the first and the second local air data parameters based on relationships determined by flight testing the system against a set of reference sensors, and based on differences between first and second local airspeeds and/or first and second local wind angles; and output the one or more freestream air data parameters to one or more aircraft consuming systems; wherein the one or more freestream air data parameters include aircraft true airspeed, TAS, or freestream air temperature. a first ultrasonic air data system, UADS, configured to sense local acoustic properties at a first location on one side of an aircraft; a first local air data module operatively connected to the first UADS and configured to determine first local air data of the first location and to output first local air data parameters including first local airspeed, first local wind angle, first local speed of sound, first local air temperature and first local Mach number; a second UADS configured to sense local acoustic properties at a second location on a second side of the aircraft, opposite the first side; and a second local air data module operatively connected to the second UADS and configured to determine second local air data of the second location and to output second local air data parameters including second local airspeed, second local wind angle, second local speed of sound, second local air temperature and second local Mach number; and a freestream data module operatively connected to the first local air data module and the second local air data module, and configured to: receive the first local air data parameters from the first local air data module; receive the second local air data parameters from the second local air data module; determine one or more freestream air data parameters based on converting the first and the second local air data parameters based on relationships determined by flight testing the system against a set of reference sensors, and based on differences between first and second local airspeeds and/or first and second local wind angles; and output the one or more freestream air data parameters to one or more aircraft consuming systems; wherein the one or more freestream air data parameters include aircraft true airspeed, TAS, or freestream air temperature. receive the first local air data parameters from the first local air data module; receive the second local air data parameters from the second local air data module; determine one or more freestream air data parameters based on converting the first and the second local air data parameters based on relationships determined by flight testing the system against a set of reference sensors, and based on differences between first and second local airspeeds and/or first and second local wind angles; and output the one or more freestream air data parameters to one or more aircraft consuming systems; wherein the one or more freestream air data parameters include aircraft true airspeed, TAS, or freestream air temperature.