Method and device for determining a safety altitude for an aircraft

The method involves determining a safety altitude from a sum of high altitude of an aircraft from ground and a protection height. A control surface defined laterally in the safety surface and vertically by the safety altitude, is determined. A location of each point of the control surface at a height corresponding to the protection height, above the ground is verified. An independent claim is also included for an aircraft having a device for determining a safety altitude of the aircraft.