Field of the Invention The invention relates to the maintenance of aircraft, and in particular fuel tanks. Specifically, the maintenance apparatus of the present invention is directed to the preparation of fuel tanks for maintenance and also maintaining of optimal ventilation during which personnel may enter the tank.

Background of the Invention In the preparation of maintenance for aircraft fuel tanks it is necessary to remove bulk fuel and residual fuel vapour from the fuel tank. In the case of larger aircraft the fuel tanks will be substantially enclosed within the wings of the aircraft. Being elongate spaces, maintenance within the fuel tank will be difficult to the extent that the fuel tank is considered a "confined space" and therefore subject to stringent safety requirements. Further, as the wing is a structural element, the fuel tank will be divided into sections separated by structural frames. Li order to conduct maintenance within this confined space, it will be necessary for the operator to navigate these frames. This further complicates the procedure in that in an emergency situation, extraction of an injured operator from a distal portion of the fuel tank is an awkward and complex exercise.

To mitigate at least a portion of the hazard involved, fuel vapour is permitted to exit the fuel tank and further, residual fuel trapped in cavities of the fuel tank is permitted to drain out using purpose built sump drains. On completion of these stages, operators may be permitted to enter the confined space after a certain period of time on the basis that said operators may use breathing apparatus and may be tethered so that in case of emergency the operators may be located and removed from the fuel tank by emergency personnel.

Despite the stringent safety precautions to be implemented, maintenance in its own right is driven by cost considerations. Therefore in meeting the safety requirements it is also necessary to streamline and make more efficient the maintenance tasks to reduce overall operating costs. It is therefore an object of the present invention to make maintenance activities more efficient particularly as they relate to aviation applications while still maintaining the high safety standards required of said activities.

Summary of Invention Therefore, in a first aspect the present invention provides a maintenance unit comprising a housing, air driven equipment said equipment including a fuel vapour purging device, and operator breathing apparatus wherein the equipment is mounted to the housing for storage and transportation as a unitary device.

It is characteristic of the equipment required for the maintenance of a fuel tank that the equipment requires a substantial air supply. Further, it will not always be possible to conduct maintenance in a hangar where available infrastructure including substantial air supply is readily available. Therefore, in order to perform the maintenance tasks offered by the present invention, remote access to an air supply for each of the stages of the maintenance process will be required. After conforming to the rigid safety requirements, efficiency is the next most critical aspect of any maintenance program. The present invention seeks to maximise the efficiency of the process by making available at a remote site not only the equipment for purging fuel vapour, and providing breathing apparatus but further to have these within a transportable unit, with the connectivity that permits a single compressor attached to the unit to service this equipment.

In a preferred embodiment the unit may further include specific functionality to transport the unit to a remote location. This functionality may include apparatus to permit the unit to be towed by various vehicles available to the maintenance staff. Alternatively or in combination with this towing apparatus, the unit may be adapted to be lifted by a forklift and so have recesses to accept forklift tines. Ih a further embodiment the unit may have lugs and/or brackets permitting the lifting of the unit by a crane. In an alternative embodiment the unit may further include a motive device permitting the unit to be self propelled. Thus, in any one of the immediately preceding embodiments the unit may be transported to the point at which the maintenance will take place by towing, lifting or placing it on the back of a flat tray truck. In a further preferred embodiment, the unit may be permanently or removably mounted to a truck.

Aircraft hangar space is at premium and so generally restricted to more critical or extensive maintenance of an aircraft. It may therefore be more efficient to conduct minor and routine maintenance of the fuel tanks at a point distant from said hangars. Further, it may be beneficial to conduct said minor and routine maintenance on the fuel tanks of several aircraft at one time. For larger aircraft where multiple points of fuel vapour extraction may be utilised, access to more than one fuel vapour purging device may assist in decreasing the cycle time for fuel tank maintenance. To this end in a preferred embodiment the maintenance unit may store a plurality of fuel vapour purging devices and may have the capacity to operate said plurality of fuel vapour purging devices simultaneously either on the same aircraft or on several aircraft positioned contiguously.

In a preferred embodiment, the equipment further includes a sump fuel drainage device for the drainage of fuel caught in interstitial portions of the tank.

In a more preferred embodiment the sump fuel may also be drained simultaneously with the purging of fuel vapour. To this end the unit may be capable of operating one or more fuel vapour purging devices simultaneously with one or more sump fuel drainage devices.

Brief Description of Drawings An embodiment of the invention will now be described, by way of example, with respect to the accompanying drawings, in which: Figure 1 is an isometric view of the maintenance unit according to the present invention; Figure 2 is a lateral cross-section of the maintenance unit of Figure 1; Figure 3 is an isometric view of a Boeing B747 aircraft; Figure 4 is a detailed view of a purger device according to a preferred embodiment of the present invention; Figure 5 is an elevation view of a fuel mist collection bag according to a preferred embodiment of the present invention; Figure 6 is an isometric view of an adapter according to a preferred embodiment of the present invention. Figure 7 is an isometric view of a B747 horizontal stabliliser; Figure 8 is an elevation view of a safety line reel according to a preferred embodiment of the present invention; Figure 9 is an air supply hose reel according to a preferred embodiment of the present invention.

Detailed Description of the Preferred Embodiment Figure 1 shows a maintenance unit 10 according to a preferred embodiment of the present invention. In this case the maintenance unit 10 is in the form of a trailer with a towing frame 30 preferably attaching it to a prime mover (not shown). Further, the maintenance unit 10 has recesses 35 which are adapted to receive the tines of a forklift so the maintenance unit 10 can be lifted to an appropriate location or on the back of a flat bed truck (not shown).

The maintenance unit 10 has a housing which has been purpose-built to contain the various pieces of necessary equipment including various storage bins 40 for ancillary equipment such as barricade chain, safety cones and spare parts for the primary equipment. To facilitate access to platform 50 in order to perform maintenance on the components located there, the maintenance unit 10 further provides steps 45 in a fixed arrangement so as to avoid the need for a ladder or other less stable means of access to the work platform 50.

To accommodate this more significant capital equipment, storage bays 20 are set into the side of the maintenance unit 10 accessible through roller shutters and so made available to maintenance personnel. Further, maintenance personnel working within the fuel tank, so as to meet safety requirements of a confined space, must be tethered to an outside structure as well as having breathing apparatus whereby the air supply is located outside the confined space. In this embodiment reels 55 A to 55D of a different coloured guide rope are provided to attach to a maximum of 4 operators. Further, hose reels 25 A and 25B are also provided to link fuel vapour purging devices to the air supply of the maintenance unit. In this embodiment and in accordance with the safety requirements for entering a confined space, the breathing apparatus will comprise an ambient air supply to avoid the issue of the operators running out of air. It follows that air is drawn through intake filter snorkels 60 which draw air into a pump within the maintenance unit 10. Said pump provides regulated air to the apparatus through the hoses and therefore satisfies the remote air supply requirement for entry into a confined space. Figure 2 shows a lateral cross-section of the maintenance unit 10. In this view the major internal chambers of the housing 15 are shown.

In this view the arrangement for the breathing apparatus can more clearly be seen. The intake filter snorkel 60 is in fluid communication with the ambient air supply to the pump 70. Said pump 70 is connected to, in this view, hose reels 85A and 85B within a storage compartment of the housing 15. Within said compartment is further located guide rope reels 55A to 55D and so in combination with the hose reels 85A and 85B provides a safety line and air supply for maintenance operators. In a further compartment is located a fuel vapour purging device (not shown) which attaches to an opening on the fuel tank in order to remove fuel vapour from the tank through a driven air supply. To this end the fuel vapour, purging device is attached to a valve on the fuel tank. To the fuel vapour purging device 75 will be attached to a hose located upon hose reels 25 A and 25B which are in fluid communication with the external air pump 67. Thus, the air supply provided by the external air pump 67 drives air into the fuel vapour purging device with the fuel vapour being drawn out from said device over a period of time. The use of said devices reduce the normal vapour extraction period from by as much as 80%. It follows that the removal of fuel vapour from the tank must be completed prior to access by maintenance personnel so as to avoid the presence of hazardous fumes in the confined space. Having access to said fuel vapour purging device within the maintenance unit 10 together with the breathing apparatus, leads to a more efficient use of capital equipment and time, thus reducing overall operating costs for the maintenance program.

Figure 3 shows a Boeing B747 aircraft 90 highlighting the locations of the primary fuel tanks 95 and 105. The diagram shows the largest single fuel tank 95 extending internally within both wings with a central portion within the main fuselage linking the two wing based fuel tank portions. Located in the horizontal stabilizer is an isolated fuel tank 100 with a larger central tank within the base of the horizontal stabilizer and extending partially within the horizontal stabilizer.

Figure 3 shows further the location of sump fuel drains in the wing 11OA to I as well as the rearwardly located fuel sump drains 115 and 120.

It is within these fuel tanks that prior to maintenance, fuel is siphoned, the sump fuel drains emptied and any remaining fuel vapour purged from the tanks.

Figure 4 shows an example of the use of a fuel vapour purging device 130 as it applies to the center tank of a B747 aircraft. The center tank 125 having purging and ventilation access panels 150 have attached thereto the purging device 130 using adapter 135. Connected to the adapter is a collapsible hose 140 which at an opposed end is attached to the purging cone 145. The process commences by opening a purge door (panel) 148 which in this example is located at the rear right upper portion of the same tank. The purging device 130 is securely grounded for safety before air is sucked out of the center tank, removing fuel vapour through the purging device 130. In a preferred embodiment of the present invention, the purging device with the adapter and 10 m of 225 mm diameter collapsible hose is stored within the maintenance unit 10 for each application of the purging device. In more preferred embodiments whereby the maintenance unit is capable of operating multiple purging devices, multiples of the collapsible hose and adapters will be stored within the maintenance unit. Figures 5 and 6 show accessories for the purging device 130. Figure 5, in particular, shows a fuel mist collector bag 155 which is attached to the outlet end of the purging cone 145 to collect the coalesced fuel vapour as it is purged from the fuel tank. In a preferred embodiment, the fuel mist collector bag 155 will be constructed with stitch cotton permeable to the air flow driving the fuel vapour from the tank. The collector bag 155 will also have a replaceable solvent pad 158 which is adapted to directly collect fuel vapour condensate or to collect run off as it collects on the cotton structure running into the solvent pad 158. In a preferred embodiment, the maintenance unit 10 may store multiple fuel mist collector bags and a box of replaceable solvent pads.

Figure 6 shows a stainless steel hose adapter 135 used for the purging device as it connects to the purging panel outlet. It is constructed to fit over the inlet and with a spigot 160 to connect directly to a collapsible hose. In a preferred embodiment, several of such adapters would be stored in order to have the purging device compatible with a range of different purging panels within a single aircraft and also for multiple types of aircraft.

Figure 7 shows a further example of two purging panels in the horizontal stabilizer tank. Said panels 165 requires a further adapter stored within the maintenance unit 10. As with the central tank, the procedure follows the process of opening panel 170 and attaching the adapter of the purging device to panel 165 to conduct the purge. Figure 8 shows the safety line reel 55 in further detail. The reel 55 is protected by a guard cover 185 which fits the safety line 175 through a feeder 180 comprising an eyelet, feeder drum and guiding tube.

Figure 9 shows the supply air hose reel 25 which delivers the supply air hose 190 through guiding arm 195 to facilitate free unwinding of the air hose.