A flight management assembly for an aircraft and method for monitoring such an assembly. The flight management assembly includes two guidance systems each provided with a flight management system, the flight management systems being independent, each of the flight management systems carrying out at least one calculation of roll commands for the aircraft, the flight management assembly also comprising a data generating unit, preferably forming part of a guidance computer, for calculating a roll command and a monitoring unit for carrying out a monitoring of the roll commands calculated by the two flight management systems and by the data generating unit in such a way as to be able to detect and identify a defective flight management system.