Method and device for determining a safe altitude for an aircraft

1. A method for determining a safe altitude for an aircraft, said method comprising:

a) defining a clear zone, corresponding to a lateral area defined in the lateral plane of the aircraft and linked to the flight of said aircraft;

b) determining the highest altitude of the ground that is located under this clear zone; and

c) determining the safe altitude as the sum of said highest altitude determined in step b) and a guard height, wherein the following operations are carried out:

determining a control area, defined laterally by said clear zone and vertically by said safe altitude; and

checking each point of said control area to ensure that it is located at at least a height corresponding to said guard height, above the ground.

2. The method as claimed in claim 1 , wherein, furthermore, in step d), at least said safe altitude is presented to a pilot of the aircraft.

3. The method as claimed in claim 1 , wherein said guard height is a predetermined height, which can be modified by an operator.

4. The method as claimed in claim 1 , wherein said guard height is around 300 meters.

5. The method as claimed in claim 1 , for an aircraft flying along a predetermined flight path comprising a lateral path provided with waypoints (P 1 A, P 1 B), wherein said clear zone is linked to said lateral path.

6. The method as claimed in claim 5 , wherein said clear zone has at least one rectangular area ( 16 , 24 , 25 ) which is centered laterally relative to a straight-line segment linking two successive waypoints (P 1 A, P 1 B) and which is defined at least over a part of said straight-line segment.

7. The method as claimed in claim 6 , wherein said clear zone has a plurality of adjacent rectangular areas.

8. The method as claimed in claim 5 , wherein said clear zone includes a circle ( 17 , 18 , 26 , 27 ) at at least one of said waypoints (P 1 A, P 1 B).

9. The method as claimed in claim 8 , wherein said circle ( 17 , 18 , 26 ) is centered on said waypoints (P 1 A, P 1 B).

10. The method as claimed in claim 8 , wherein said circle ( 27 ) is centered on a point of intersection of two successive straight-line segments associated with said waypoint (P 1 B), when the flight at said waypoint (P 1 B) presents an obligation to fly over the latter.

11. The method as claimed in claim 1 , for an aircraft which is in free flight, wherein said clear zone ( 3 ) is linked to the current position of the aircraft.

12. The method as claimed in claim 11 , wherein said clear zone presents a length which corresponds to a predetermined flight time of the aircraft at the current speed.

13. The method as claimed in claim 11 , wherein said clear zone presents a length which depends on a longitudinal scale of a display screen on the aircraft.

14. The method as claimed in claim 11 , wherein said clear zone presents a width which takes into account an uncertainty concerning said current position of the aircraft.

15. The method as claimed in claim 11 , wherein said clear zone presents a conical shape.

16. The method as claimed in claim 1 , wherein said clear zone can be modified by an operator.

17. The method as claimed in claim 1 , wherein a safe altitude profile is determined, taking into account any variation of the safe altitude at least forward of the current position of the aircraft.

18. A device for determining a safe altitude for an aircraft, said device comprising:

means for determining a clear zone corresponding to a lateral area dependent on the flight of the aircraft;

means for determining the highest altitude of the ground that is located under this clear zone; and

means for determining the safe altitude, by calculating the sum of said highest altitude and a guard height, which also includes, to control said safe altitude, means which determine a control area defined laterally by said clear zone and vertically by said safe altitude and which check that each point of said control area is located at at least a height corresponding to said guard height, above the ground.

19. The device as claimed in claim 18 , which also includes display means for presenting at least said safe altitude on at least one display screen.

20. An aircraft, which includes a device such as the one specified in claim 18 .

21. An aircraft, which includes a device for implementing the method specified in claim 1 .