A method of automatically triggering an emergency
buoyancy system (10) for a
hybrid helicopter (20) having a
fuselage (21), two half-wings (23, 23′), and two propulsive propellers (24, 24′). During the method, said emergency
buoyancy system (10) is primed, and then if a risk of said
hybrid helicopter (20) ditching is detected, two retractable wing undercarriages (28, 28′) are deployed, each wing undercarriage (28, 28′) being fastened under a respective half-wing (23, 23′) and being provided with at least one immersion sensor (16). Finally, if the beginning of said
hybrid helicopter (20) ditching is detected, at least one main
inflatable bag (11, 11′) 7B suitable for being arranged under such
fuselage (21) and at least one secondary
inflatable bag (12, 12′) suitable for being arranged under each half-wing (23, 23′) are inflated so as to ensure that said hybrid helicopter (20) floats in stable manner.