Disclosed are an airplane system including duplex modules, and a control method thereof. The control method of the airplane system includes: receiving, by each of a plurality of duplex modules, a corresponding event command from a client; performing, by a first module, a first event specified by the event command in response to the event command; performing, by a second module different from the first module, a second event specified by the event command after the first event is completed; and returning a first response signal indicating a result of the performance of the first event and a second response signal indicating a result of the performance of the second event to the client, in which the client compares the first response signal and the second response signal, and determines whether the plurality of duplex modules is synchronized or has an error.