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An aircraft engine nacelle nose cowl has a supply duct to deliver pressurised hot gas into an internal compartment of the nose cowl. A slot is provided in the nose cowl to enable pressurised hot gas to pass out of the compartment through the slot. As the pressurised hot gas passes out of the compart

An aircraft engine nacelle nose cowl has a supply duct to deliver pressurised hot gas into an internal compartment of the nose cowl. A slot is provided in the nose cowl to enable pressurised hot gas to pass out of the compartment through the slot. As the pressurised hot gas passes out of the compartment through the slot, this causes a film of water on an outer surface of the nose cowl to detach from the nose cowl. The slot is of restricted dimensions which causes localised heating of the nose cowl around the slot as the pressurised hot gas pass out of the compartment through the slot. In this manner ice is prevented from accumulating on the outer surface of the nose cowl and/or ice is removed from the outer surface of the nose cowl.

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1. A system for use with a structure comprising an aircraft engine nacelle nose cowl to protect the structure from accumulation of ice on at least part of an outer surface of the structure, the system comprising:means to deliver pressurised gas into an internal compartment of the structure; and at l

1. A system for use with a structure comprising an aircraft engine nacelle nose cowl to protect the structure from accumulation of ice on at least part of an outer surface of the structure, the system comprising:means to deliver pressurised gas into an internal compartment of the structure; and at least one aperture in the structure to facilitate passage of gas out of the compartment; the at least one aperture being located so as to extend in a circumferential direction around an inward side of the nose cowl and configured for passage of gas out through the aperture at an angle in the range of from about 45° to 90° to the direction of airflow over the outer surface of the structure and at a momentum sufficient to detach a film of water from an outer surface of the structure. 2. A system as claimed in claim 1 wherein the aperture is of restricted dimensions to cause localised heating of the structure around the aperture upon passage of gas out through the aperture.3. A system for use with a structure comprising an aircraft engine nacelle nose cowl to protect the structure from accumulation of ice on at least part of an outer surface of the structure, the system comprising:means to deliver pressurised gas into an internal compartment of the structure; and at least one aperture in the structure to facilitate passage of gas out of the compartment, at an angle in the range of from about 45° to 90° to the direction of airflow over the outer surface of the structure and; the at least one aperture being located so as to extend in a circumferential direction around an inward side of the nose cowl and of restricted dimensions to cause localised heating of the structure around the aperture upon passage of gas out through the aperture. 4. A system as claimed in claim 3 wherein the aperture is located upstream of the aircraft engine air intake.5. A system as claimed in claim 3 wherein the compartment is a forward compartment formed by a forward bulkhead and an inner surface of the structure extending forwardly of the forward bulkhead.6. A system as claimed in claim 5 wherein the forward bulkhead is attached to the structure by means of a passage member.7. A system as claimed in claim 3 wherein the system comprises means to direct the gas towards the aperture.8. A system as claimed in claim 7 wherein the directing means is arranged to direct gas out through the aperture at an angle in the range of from about 45° to about 90° to the direction of airflow over the outer surface of the structure.9. A system as claimed in claim 8 wherein the directing means is arranged to direct gas out through the aperture substantially normal to the direction of airflow over the outer surface of the structure.10. A system as claimed in claim 7 wherein the directing means comprises a passage to channel the gas towards the aperture.11. A system as claimed in claim 10 wherein the passage is formed by two or more opposed passage members.12. A system as claimed in claim 11 wherein a forward one of the passage members is attached to an inner surface of the structure.13. A system as claimed in claim 12 wherein a rearward one of the passage members is attached to an outer surface of the structure.14. A system as claimed in claim 10 wherein the transverse dimension of the passage is substantially equal to the transverse dimension of the aperture.15. A system as claimed in claim 10 wherein the system comprises means to diffuse the gas as it passes through the passage.16. A system as claimed in claim 15 wherein the diffusing means comprises one or more baffles in the passage.17. A system as claimed in claim 3 wherein the aperture is in the form of a slot.18. A system as claimed in claim 17 wherein the slot extends in a circumferential direction around at least part of the structure.19. A system as claimed in claim 18 wherein the slot extends around the entire circumference of the structure.20. A system as claimed in claim 17 wherein the slot extends substantially transverse to the direction of airflow over the outer surface of the structure.21. A system as claimed in claim 17 wherein the slot is of sawtooth form.22. A system as claimed in claim 17 wherein the slot comprises a plurality of slots.23. A system as claimed in claim 22 wherein the slots are located in a row.24. A system as claimed in claim 23 wherein the plurality of slots comprises a plurality of slot rows.25. A system as claimed in claim 24 wherein the slot rows are staggered.26. A system as claimed in claim 3 wherein the gas temperature is in the range of from about 80° C. to about 200° C.27. A system as claimed in claim 26 wherein the gas temperature is approximately 140° C.28. A system as claimed in claim 3 wherein the structure at least partially comprises an aluminium alloy material.29. A system as claimed in claim 3 wherein the structure at least partially comprises adhesive-bonded materials.30. A system as claimed in claim 3 wherein the means to deliver gas into the compartment comprises a supply duct.31. A system as claimed in claim 30 wherein the means to deliver gas into the compartment comprises an apertured spray ring in communication with the supply duct.32. A system as claimed in claim 3 wherein the system further comprises electrical heating means configured to heat the structure.33. A method of protecting a structure comprising an aircraft engine nacelle nose cowl from accumulation of ice on at least part of an outer surface of the structure, the method comprising the steps of:delivering pressurised gas into an internal compartment of the structure; and passing the gas out of the compartment at an angle in the range of from about 45° to 90° to the direction of airflow over the outer surface of the structure and at a momentum sufficient to detach a film of water from an outer surface of the structure wherein said at least one aperture is located so as to extend in a circumferential direction around an inward side of the nose cowl. 34. A method as claimed in claim 33 wherein the aperture is of restricted dimensions to cause localised heating of the structure around the aperture upon passage of the gas out through the aperture.35. A method of protecting a structure comprising an aircraft engine nacelle nose cowl from accumulation of ice on at least part of an outer surface of the structure, the method comprising the steps of:delivering pressurised gas into an internal compartment of the structure; and passing the gas out of the compartment at an angle in the range of from about 45° to 90° to the direction of airflow over the outer surface of the structure and through at least one aperture located so as to extend in a circumferential direction around an inward side of the nose cowl and of restricted dimensions in the structure the aperture to cause localised heating of the structure around the aperture. 36. A method as claimed in claim 35 further comprising the step of directing the gas towards the aperture.37. A method as claimed in claim 36 further comprising the step of directing the gas out through the aperture substantially normal to the direction of airflow over the outer surface of the structure.38. A method as claimed in claim 36 further comprising the step of diffusing the gas upon passage out of the compartment through the aperture.39. A method as claimed in claim 35 wherein the gas is delivered into the compartment at a temperature in the range of from about 80° C. to about 200° C.40. A method as claimed in claim 39 wherein the gas is delivered into the compartment at a temperature of approximately 140° C.