An aircraft (100, 200) comprising a crash attenuation system, the system comprising: an airbag assembly (111, 211) carried by the aircraft (100, 200) and inflatable generally adjacent an exterior of the aircraft, the airbag assembly (111, 211) comprising an airbag (112, 212, 213, 214, 215, 402) and a vent system, wherein the vent system comprises a vent passage supported by the aircraft, the vent passage having a continuously adjustable vent area through which gas can escape from within the first airbag; a gas source system in fluid communication with an interior of the airbag (112, 212, 213, 214, 215, 402); a sensor system (130, 302) for detecting selected crash conditions; and a control system (126, 354) for controlling rate at which gas can escape from within the airbag (112, 212, 213, 214, 215, 402) through the vent passage (122, 408) based on the detected crash conditions; wherein the vent passage (122, 408) extends between a first opening in the vent passage and a second opening in the vent passage (122, 408); and wherein the first opening is in fluid communication with the interior of the airbag (112, 212, 213, 214, 215, 402), and the second opening is open to the ambient air, and is positioned beyond an outermost extent of the airbag when the airbag (112, 212, 213, 214, 215, 402) is inflated; and characterised in that the vent passage (122, 408) is at least long enough to extend beyond the upper portion of the airbag (112, 212, 213, 214, 215, 402); and i) the upper side of the vent passage (122, 408) is flush with the under side of the fuselage; or ii) the bottom side of the vent passage (122, 408) is flush with the under side of the fuselage; and the vent passage is at least partially contained within the fuselage 416 of the aircraft (100,200). an airbag assembly (111, 211) carried by the aircraft (100, 200) and inflatable generally adjacent an exterior of the aircraft, the airbag assembly (111, 211) comprising an airbag (112, 212, 213, 214, 215, 402) and a vent system, wherein the vent system comprises a vent passage supported by the aircraft, the vent passage having a continuously adjustable vent area through which gas can escape from within the first airbag; a gas source system in fluid communication with an interior of the airbag (112, 212, 213, 214, 215, 402); a sensor system (130, 302) for detecting selected crash conditions; and a control system (126, 354) for controlling rate at which gas can escape from within the airbag (112, 212, 213, 214, 215, 402) through the vent passage (122, 408) based on the detected crash conditions; wherein the vent passage (122, 408) extends between a first opening in the vent passage and a second opening in the vent passage (122, 408); and wherein the first opening is in fluid communication with the interior of the airbag (112, 212, 213, 214, 215, 402), and the second opening is open to the ambient air, and is positioned beyond an outermost extent of the airbag when the airbag (112, 212, 213, 214, 215, 402) is inflated; and characterised in that the vent passage (122, 408) is at least long enough to extend beyond the upper portion of the airbag (112, 212, 213, 214, 215, 402); and i) the upper side of the vent passage (122, 408) is flush with the under side of the fuselage; or ii) the bottom side of the vent passage (122, 408) is flush with the under side of the fuselage; and i) the upper side of the vent passage (122, 408) is flush with the under side of the fuselage; or ii) the bottom side of the vent passage (122, 408) is flush with the under side of the fuselage; and the vent passage is at least partially contained within the fuselage 416 of the aircraft (100,200).