A method and system for determining an airspeed of an aircraft, known as assisted aircraft, comprises: a) determining a position; b) measuring a ground speed; c) receiving a plurality of messages from a plurality of other assisting, aircraft, each message containing a first item of information, indicating a position of an assisting aircraft, and a second item of information, indicating a wind speed at the position; d) estimating a wind speed at the position of the assisted aircraft by interpolating the wind speed values at the positions of the assisting aircraft obtained in step c); and e) computing a true speed of the assisted aircraft by using the vector difference between its ground speed, measured in step b), and the wind speed estimated in step d). The method can check operation of an anemometric subsystem aboard an aircraft, to compensate for any malfunction and/or to enable automatic piloting.