The communication apparatus (1100) configured to be installed in a first aircraft (1b) comprises a controller (1110) and a transmitter (1106). The controller (1110) is configured to acquire resource information and determine a communication condition based on the resource information, the resource information being related to a second aircraft (1a) different from the first aircraft (1b) or to a radio altimeter installed in the second aircraft (1a). The transmitter (1106) is configured to transmit transmission data to one other communication apparatus installed in the first aircraft (1b), according to the communication condition.