Abstract: An aircraft defueling system includes a fuel jettison port (10) extending between the bottom side of a fuel tank (11) an the exterior of an aircraft. The port is sealed with a glass closure (12). A cylinder (13) with a piston (17) therein is positioned above the glass closure. A pressurized inert gas bottle (23) is connected to an expandable chamber (28) between the top ends of the cylinder and the piston. A metering port (27) is arranged on the side of the cylinder below the piston. Just prior to an unavoidable crash, a valve (25) on the gas bottle is opened to force the piston downwardly, so that the glass closure is broken by a conical bottom extension (18) on the piston. The piston is moved past the metering port. The inert gas is released into the fuel tank through the metering port, so as to pressurized the fuel tank and rapidly jettison the fuel through the port.