An on-board maintenance system for an aircraft, said aircraft comprising pieces of equipment connected together through a first on-board data transmission network for exchanging operational data intended for piloting the aircraft, said maintenance system including a processing unit and being characterized in that it comprises a second data transmission network, distinct from the first network, for exchanging data intended for maintenance of the equipment of the aircraft, said second network connecting at least some of said pieces of equipment to the processing unit; said processing unit are being adapted for receiving in real time, a data provided by the pieces of equipment on the second network and processing them with view to determining the cause of equipment malfunctions according to at least said received data.