carrier is detected yes the process goes to step st 304 in st 304 the radio waves at the frequency f 1 are demodulated to detect the id code the detected id code is checked to determine whether it is the same as the set id code since an id code is inserted every time the frequency changes the id code is detected every time the frequency hops when the detected id code is the same as the set id code yes the process goes to step st 305 when the detected id code is not the same as the set id code no the process returns to step st 302 in step st 305 control information is received the control information relates to for example control of a rudder of a horizontal stabilizer and so on the control signal also includes information regarding conditions where no control is exercised in step st 306 control information such as that regarding control of the rudder of a horizontal stabilizer and so on is sent to the servomechanisms in step st 307 the next frequency is received after a predetermined time with the radio zone x 1 the frequency f 2 is set as the next frequency the predetermined time is the time elapsed since immediately after the id was detected in step st 304 the time between the id detection and the change from the current frequency to the next frequency is always.