Aircraft assembly

1. An aircraft assembly in an aircraft, the aircraft assembly comprising:

a mount for an aircraft engine;

a wing;

first and second tension bolts arranged to suspend the mount below the wing, the first and second tension bolts connected to the wing such that a lower end of each of the first and second tension bolts extend below a lower surface of the wing and are accessible from respective outer surfaces of the mount and the wing, wherein the first and second tension bolts each include a longitudinal axis oriented substantially vertically while the aircraft is on ground and the first and second tension bolts extend downward through the lower surface of the wing; and

first and second fail-safe mechanisms each associated with a respective one of the first and second tension bolts and arranged to suspend the mount below the wing responsive to failure of a respective first or second tension bolt.

2. The aircraft assembly according to claim 1 , wherein the first and second fail-safe mechanisms are arranged not to suspend the mount below the wing when there is no failure of the respective first or second tension bolt.

3. The aircraft assembly according to claim 1 , wherein the first and second tension bolts are connected to the mount via flanges on the outer surfaces of mount.

4. The aircraft assembly according to claim 1 , wherein the first and second tension bolts each comprise a head, a shaft and a retaining nut, and

wherein the first and second tension bolts are each arranged such that the retaining nut is at the lower end of the respective first or second tension bolt that is accessible from the respective outer surface of the mount.

5. The aircraft assembly according to claim 1 , comprising first and second shear attachments connecting the mount and the wing, wherein the shear attachments are arranged to receive a primary load in a shear direction.

6. The aircraft assembly according to claim 1 , wherein the mount is an engine mounting pylon and the wing includes a wing box comprising a front spar, and

wherein the first and second tension bolts connect the engine mounting pylon to the front spar.

7. The aircraft assembly according to claim 1 , wherein the at least one of the first and second fail-safe mechanisms comprises a fail-safe fastener arranged in a parallel direction to the longitudinal axis of the respective first or second tension bolt.

8. The aircraft assembly according to claim 7 , wherein the fail-safe fastener is rotatable about a longitudinal axis of the fail-safe fastener when the respective first or second tension bolt is in use.

9. The aircraft assembly according to claim 7 , wherein the fail-safe fastener is separated from the respective first or second tension bolt by a separating structure.

10. The aircraft assembly according to claim 7 , wherein the fail-safe fastener extends through a central bore of the respective first or second tension bolt.

11. The aircraft assembly according to claim 1 , comprising a structural health monitoring system associated with each of the first and second tension bolts.

12. An aircraft comprising an aircraft assembly according to claim 1 .

13. An aircraft assembly of an aircraft, the aircraft assembly comprising:

an engine mounting pylon configured to attach an aircraft engine to an aircraft wing;

a wing box;

first and second tension bolts connecting the engine mounting pylon to the wing box in tension, wherein a lower end of each of the first and second tension bolts are below a lower surface of the wing box and are accessible from external surfaces of the engine mounting pylon, wherein the first and second tension bolts each include a longitudinal axis oriented substantially vertically while the aircraft is on ground and the first and second tension bolts extend downward through the lower surface of the wing box, and

first and second fail-safe arrangements each associated with a respective one of the first or second tension bolts, and arranged to support the engine mounting pylon relative to the wing box responsive to failure of the respective first or second tension bolt.

14. A method of mounting an engine mounting pylon to a wing box of an aircraft wing on an aircraft, the method comprising:

attaching the engine mounting pylon to the wing box with first and second shear attachments;

connecting the engine mounting pylon to the wing box with first and second tension bolts arranged such that a lower end of each of the first and second tension bolts are below a lower surface of the wing box and are accessible from external surfaces of the engine mounting pylon, and an upper end of each of the first and second tension bolts is held captive in the wing box, wherein the first and second tension bolts each include a longitudinal axis oriented substantially vertically while the aircraft is on ground and the first and second tension bolts extend downward through the lower surface of the wing box;

connecting the engine mounting pylon to the wing box with first and second fail-safe mechanisms such that the fail-safe mechanisms are arranged to support the engine mounting pylon relative to the wing box responsive to failure of a respective one of the first and second tension bolts; and

tensioning the first and second tension bolts to a predetermined tension by applying a tensioning force to an end of each of the tension bolts accessible from the respective external surfaces of the engine mounting pylon.