Aircraft provided with a buoyancy system, and a buoyancy method

An aircraft having an airframe that extends longitudinally along an anteroposterior plane, the airframe extending transversely from a left side to a right side, and in elevation from a bottom to a top, the aircraft having a buoyancy system, the buoyancy system being provided with at least one pair of two floats, two distinct floats of a pair being arranged transversely on opposite sides of the anteroposterior plane, wherein the buoyancy system is provided for each float with at least one slide mounted to slide relative to a rail, each rail extending in elevation, each slide being attached to a corresponding float, each float is movable in elevation from a bottom position to a top position by each slide fastened to a float sliding along a rail, each float presenting a center of gravity present in a top plane perpendicular to the anteroposterior plane when in the top position, and in a bottom plane when in the bottom position, the bottom plane being parallel to the top plane and being situated below the top plane when the aircraft presents a roll angle of zero, the buoyancy system including, for each float a blocking system for blocking each float by default in the bottom position, and for blocking the floats present on one of the sides only of the aircraft in the top position under a predetermined condition.