A flight management assembly of an aircraft and method of monitoring the flight management assembly. The assembly includes two flight management systems, and a monitoring and backup unit, each of the flight management systems configured for generating data including a trajectory and a prediction of a parameter of the aircraft, one of the flight management systems being active and the other being passive, the monitoring and backup unit configured for carrying out monitoring of at least one of the items of data generated by the active flight management system in order to verify if the item of data is valid, the flight management assembly carrying out, in case of validation of the monitored item of data, a synchronization of the monitoring and backup unit and of the passive flight management system, with data called synchronization data of the active flight management system, namely a flight plan and/or a flight trajectory.