Aircraft often need to be defueled prior to performing certain types of maintenance or repairs. There are generally three stages of aircraft defueling: pumping (removing the majority of fuel from the aircraft fuel cells), bottom sumping (removing most of the remaining fuel from the bottom of the fuel cells—traditionally done by some type of gravity feed), and depuddling (which involves removing the small puddles remaining in the fuel cells). A number of aircraft defueling systems have traditionally been available to handle the various stages of aircraft defueling. At some point, however, most defueling systems require some type of gravity feed, resulting in low drain rates and long drain times. In fact, for many large aircraft, depending on the amount of fuel remaining in the tanks, it can take up to several hours to fully defuel the aircraft using a gravity dependent system.
More recent defueling systems include a vacuum assist to increase the defueling rate. Vacuum assist defueling systems can evacuate airplane fuel tanks in a fraction of the time normally allocated to a gravity system. Nevertheless, many vacuum assist systems are only useful with specific fuel drain configurations. Thus, the use of such vacuum assist systems is limited to certain aircraft and certain personnel trained to match an inventory of attachments with the design requirements of fuel drain systems of particular aircraft.
Accordingly, a universal coupler described in U.S. Pat. No. 5,117,876 (“the '876 patent”), which is incorporated in its entirety herein by this reference, is intended for use with nearly all aircraft. However, attaching the universal coupler to certain aircraft can be a challenge. Some airplanes, for example, have a surface radii of curvature at drain fuel drain locations that prevent standard universal connectors from being easily attached to the drain valves. Therefore, there is a need for an aircraft defueling apparatus that can be used in a variety of environments, including with aircraft that have contoured surfaces around their drain valves, to minimize the risk of fuel leaks.