A generator of inert gas from an airflow, in an inerting system for at least one aircraft fuel tank is disclosed. The generator includes a system with an air inlet and means for distributing the airflow to a plurality of air separation modules arranged in parallel on the air system to deplete oxygen in the air and generate a nitrogen-enriched inert gas at the outlet. The generator also includes a programed control unit for the distribution means to selectively supply air to a single, a portion or all of the air separation modules, depending on the flight phase of the aircraft.