A data communication system including a plurality of aircrafts and being configured to perform data communication between the plurality of aircrafts, wherein each of the plurality of aircrafts includes: - a flight mechanism; - a detection sensor configured to acquire positional information of other aircrafts than an own aircraft and a third party, the third party configured to detect the data communication performed between the plurality of aircrafts, - a location sensor configured to acquire positional information of the own aircraft; - a communicator configured to perform communication between a communicator of the own aircraft and a communicator of another aircraft by means of wireless communication, and configured to transmit and receive various pieces of data therebetween in a mutual fashion; - a controller; and - a storage that contains map data including terrain information, third party information, and a data communication program that causes the controller to implement a method that performs the data communication between the plurality of aircrafts, the terrain information being information on terrain on periphery of the plurality of aircrafts; _ wherein controllers of third aircrafts (10B, 10C) of the plurality of aircrafts are configured to select a fourth aircraft from the third aircrafts (10B, 10C) when transmission of transmission data from a first aircraft to a second aircraft out of the plurality of aircrafts (10, 10A, 10B, 10C, 10D) is not successful, the third aircrafts (10B, 10C) being remaining aircrafts out of the plurality of aircrafts (10, 10A, 10B, 10C, 10D) excluding the first aircraft and the second aircraft and being successful in receiving the transmission data from the first aircraft, the fourth aircraft being lowest in a possibility that the data communication is detected by the third party out of the third aircrafts (10B, 10C) on a basis of the positional information of each of the third aircrafts (10B, 10C), the terrain information, and the positional information of the third party, and wherein a controller of the fourth aircraft is configured to transmit the transmission data to the second aircraft. - a flight mechanism; - a detection sensor configured to acquire positional information of other aircrafts than an own aircraft and a third party, the third party configured to detect the data communication performed between the plurality of aircrafts, - a location sensor configured to acquire positional information of the own aircraft; - a communicator configured to perform communication between a communicator of the own aircraft and a communicator of another aircraft by means of wireless communication, and configured to transmit and receive various pieces of data therebetween in a mutual fashion; - a controller; and - a storage that contains map data including terrain information, third party information, and a data communication program that causes the controller to implement a method that performs the data communication between the plurality of aircrafts, the terrain information being information on terrain on periphery of the plurality of aircrafts; _ wherein controllers of third aircrafts (10B, 10C) of the plurality of aircrafts are configured to select a fourth aircraft from the third aircrafts (10B, 10C) when transmission of transmission data from a first aircraft to a second aircraft out of the plurality of aircrafts (10, 10A, 10B, 10C, 10D) is not successful, the third aircrafts (10B, 10C) being remaining aircrafts out of the plurality of aircrafts (10, 10A, 10B, 10C, 10D) excluding the first aircraft and the second aircraft and being successful in receiving the transmission data from the first aircraft, the fourth aircraft being lowest in a possibility that the data communication is detected by the third party out of the third aircrafts (10B, 10C) on a basis of the positional information of each of the third aircrafts (10B, 10C), the terrain information, and the positional information of the third party, and wherein a controller of the fourth aircraft is configured to transmit the transmission data to the second aircraft.