Method for monitoring at least one avionics system linked to a shared communication medium comprising various monitored operational systems (115-1, 115-2) composed in particular of one or more active elements, this method being characterised in that it comprises the following two phases: - a preliminary analysis phase comprising the following steps: determination of the communication streams in the shared communication medium; - functional analysis of the shared communication medium; - analysis of the conditions of alarm activation for each alarm of the said operational system; - storage of the said conditions of activation of the said at least one alarm and of an identification of the said at least one alarm; - a second monitoring phase based on the modelling during the preliminary phase comprising the following steps: - reception of fault messages in respect of the operational systems; - determination of the state of the said at least one active element of the said communication medium with the aid of a different specific link from the said communication medium; - evaluation of a state indicator of the said communication medium on the basis of the said state of the said at least one active element of the said communication medium and on the basis of the conditions of activation of alarms stored in the analysis phase; and, - selection and activation of an alarm according to the said evaluated state of the said communication medium and according to conditions of activation of the said alarm and of an identification of the said alarm. - a preliminary analysis phase comprising the following steps: determination of the communication streams in the shared communication medium; - functional analysis of the shared communication medium; - analysis of the conditions of alarm activation for each alarm of the said operational system; - storage of the said conditions of activation of the said at least one alarm and of an identification of the said at least one alarm; - a second monitoring phase based on the modelling during the preliminary phase comprising the following steps: - reception of fault messages in respect of the operational systems; - determination of the state of the said at least one active element of the said communication medium with the aid of a different specific link from the said communication medium; - evaluation of a state indicator of the said communication medium on the basis of the said state of the said at least one active element of the said communication medium and on the basis of the conditions of activation of alarms stored in the analysis phase; and, - selection and activation of an alarm according to the said evaluated state of the said communication medium and according to conditions of activation of the said alarm and of an identification of the said alarm. - reception of fault messages in respect of the operational systems; - determination of the state of the said at least one active element of the said communication medium with the aid of a different specific link from the said communication medium; - evaluation of a state indicator of the said communication medium on the basis of the said state of the said at least one active element of the said communication medium and on the basis of the conditions of activation of alarms stored in the analysis phase; and, - selection and activation of an alarm according to the said evaluated state of the said communication medium and according to conditions of activation of the said alarm and of an identification of the said alarm.