The present invention relates to the cargo aircraft sector and refers to a cargo door with a fail-safe locking mechanism for locking the door in a closed condition.

Commercial aircraft are usually equipped with a multiplicity of entry and exit openings at the bottom of the aircraft fuselage to allow loading and unloading of baggage, cargo and the like into and out of the hold, and doors suitable for closing such openings. Some cargo doors swing outwards; these doors are designed in such a way that the interior cabin of the aircraft may be pressurized only when the doors are fully and correctly closed and locked. For this purpose, one or more relatively small vent panels are made in the cargo door, with the operating mechanisms of the cargo door and the vent panel connected together in such a way that the closure of the vent panels is precluded if the cargo door is not completely and correctly closed and locked; thus, the pressurization of the internal compartments of the aircraft is prevented until every single door is closed, latched and locked.

The current Large Cargo Door fitted to cargo aircraft in use has a locking mechanism which is controlled by a vent panel controlled by the same shaft that actuates the closing/opening of the cargo door. If the cargo door locking and unlocking mechanism is defective, the vent panel will either not close or not open, depending on the condition of the panel at the time the mechanism fails. In this way, the presence of a fault is indicated.

Current cargo door locking mechanisms do not ensure verification under all conditions, including in the event that one of the components of the locking mechanism has failed.

In short, the present invention proposes to provide a locking mechanism equipped with a double drive shaft, the operation of which is ensured even in the presence of a failure of one of the shafts, capable of operating the vent panel by correctly signaling the locking of the latches. The two shafts are coaxial, whereby the size of the double shaft is the same as that of a single shaft. The inner shaft benefits from the protection of the outer shaft both with respect to aggressive chemicals and mechanical or thermal effects. An exemplary and preferential but non-limiting embodiment of the invention will now be described, with reference to the appended drawings, in which

Fig. 1 is an inside view of a cargo door depicted in the closed position, where some parts have been removed for the sake of clarity, showing in particular those parts of the actuation mechanism used to lock/unlock the cargo door;

Fig. 2 is a side view of a double torsion shaft forming part of the mechanism of the cargo door of Fig. 1 ;

Figs. 2A and 2B are enlarged views of two details of Fig. 2;

Fig. 3 is a detail on an enlarged scale, indicated with III in Fig. 2, of a joint between the two shafts, inner and outer, of the double torsion shaft; and

Fig. 4 is a schematic view of an end part of an inner shaft.

Referring initially to Fig. 1, a cargo door is indicated as a whole with the reference number 10. The illustrated cargo door is, in this example, an outward-opening swinging door adapted to be hinged to the body structure of an aircraft fuselage along a horizontal hinge axis extending along an upper edge of a compartment (not shown) formed in the fuselage and closable by said cargo door.

The cargo door 10 comprises one or more vent panels 11 (in the illustrated configuration only one is provided) to allow the inner compartments of the aircraft cabin to be pressurized during flight operations and, at the same time, to allow the internal pressure of the cabin and the external pressure to be equalized in preparation for opening the cargo door.

The cargo door is locked in a fully closed position by a locking mechanism indicated as a whole with 12, which includes a plurality of latch locking devices 13 mounted on the inner face of the cargo door. The locking devices 13 are horizontally spaced near a lower horizontal edge 15 of the cargo door. The locking mechanism 12 comprises a horizontal torsion shaft 14 extending near the lower horizontal edge 15 of the cargo door. The torsion shaft 14 serves to support and rotationally drive a plurality of actuation pins 19 which lock and unlock the locking devices 13.

The locking mechanism 12 comprises a manually operated control handle 16, known per se, which assumes a closed position flush with the outer surface of the fuselage skin. The torsion shaft 14 also serves to transmit a rotational torque to an actuation shaft 20 of the vent panel 11.

The control handle 16 is attached to a control shaft 17 which, by means of a drive 18, is coupled to the torsion shaft 14.

The torsion shaft 14 is a double “fail-safe” shaft, composed of two coaxial shafts 21, 22, mechanically connected at both ends, which ensure the transmission of motion from the control handle 6 towards each actuation pin 19, even if one of the two coaxial shafts loses integrity.

The double torsion shaft 14 comprises an inner or central control shaft 21 and an outer tubular drive shaft 22.

The various locking devices 13, six in number in the example illustrated in Fig. 1, are distributed over a considerable distance, which requires an overall long torsion shaft 14.

For constructive and assembly requirements, it is preferable to divide the torsion shaft into several segments joined together. The outer control shaft 22 may therefore be composed of a plurality of tubular segments, in this example three in number, axially aligned and joined together, preferably in a removable way (for example by means of bolts 23, Fig. 3) and rigidly integral with the inner control shaft 21, so that the double shaft 14 controlled by the control handle 16 transmits the movement to the actuation pins 9 and to the vent panel 11. The two shafts making up the torsion shaft 14 are preferably made of steel. Some bearings adapted to support rotatably the torsion shaft 14 on the cargo door are schematically indicated with 26, 27 (Figs. 2, 2A, 2B).

For constructional and assembly reasons, the inner shaft 21 may be composed of two joined steel tubes of adequate size which are inserted inside the outer tubular control shaft.

The tubes making up the inner shaft 21, rigidly integral with the outer tube 22, ensure the integrity of the locking system and, consequently, the transmission of the motion from the control handle 16 to the actuation pins 19 and to the vent panel 11 also in the event wherein the outer drive shaft has suffered a failure (for example due to corrosion, shock, or heat).

Operating on the control handle 16, the torsion shaft 14 transmits the movement to the actuation pins 19 which lock the locking devices of the cargo door. The vent panel 11 is closed when the handle 16 actuates the mechanism for locking the door, allowing the cabin to be pressurized, which remains hermetically sealed. In the event that the vent panel 11 remains open due to a failure in the drive system (for example due to breakage of the torsion shaft), pressurization may not take place because the “cut-out” hole (hermetically closed when the vent panel is closed) is not closed and discharges the air to the outside.

Since current standards permit the failure of a single device of a plurality of locking devices 13, it is permissable that the torsion shaft 14 does not extend in its double shaft configuration along its entire length. As shown in Fig. 1 and 3, a portion of the torsion shaft 14 may have only one of the two inner or outer shafts. In the example shown, an intermediate portion of the torsion shaft 14 which actuates the third from the left of the locking devices 13, has only the inner control shaft 21 and has no outer control shaft 22.

Preferably, the inner shaft 21 or the segments that compose it are joined to the outer shaft 22, and/or to the segments that compose it, only in proximity to the opposite ends of the inner shaft or the relative segments.

To facilitate the assembly and possible disassembly of the torsion shaft 14 in the event of maintenance, and in particular to facilitate the insertion of the inner shaft into the outer one, the inner shaft 21 has a smaller outer diameter than the inner diameter of the outer shaft 22. In this way, the cylindrical surface of the main part of the inner shaft is not in contact with, and therefore does not rub against, the inner cavity of the outer shaft.

At the ends of each inner shaft 21 or segment that composes it, two centering bushings 24 may be mounted, each interposed between the inner cavity of the outer shaft 22 and one end of the inner shaft 21 or a segment that composes it. The bushings 24 may be inserted on the ends 25 (Fig. 4) of the inner shaft having smaller diameters or transverse dimensions than the outer diameter of the main part of said inner shaft. The bushings 24 ensure the coaxiality of the inner and outer shafts. As may be appreciated, the outer shaft exerts a chemical, mechanical and thermal protective action with regard to the innermost shaft. The proposed solution ensures the functionality and monitoring of the cargo door lock system in all conditions including the occurrence of an individual fault.