Abstract: An energy absorbing structural unit is attached outside the fuselage belly of an aircraft having at least two decks arranged one over another. At least the lower deck, of which the floor is adjacent to the fuselage belly, includes passenger cabin compartments and/or service facilities. The energy absorbing structure is an energy absorbing structural unit (5) that is attached outside of the existing aircraft fuselage (2) approximately vertically below the passenger cabin compartment (9) and/or service facilities provided on the lower deck of the aircraft. The energy absorbing structural unit absorbs impact energy arising in a crash or emergency landing of the aircraft. Because impact energy is absorbed by the external structural unit rather than or in addition to the structure of the aircraft fuselage and air frame, it is possible to provide lower deck passenger cabin space that may be continuously occupied by passengers and crew even during the take-off and landing phases of a flight.