A warning is generated if the altitude loss is excessive for the accumulated time-altitude product after take-off (38, 40).
This problem is solved by comparing the accumulated altitude loss after take-off (12, 14, 62, 34) with the product of a barometrically derived altitude and the length of time the aircraft has been flying (12, 14, 30, 32, 34).
According to a second embodiment, the height-lowering means is in the form of a cable, one end of which is provided with an anchoring means, while the other end is connected to the user harness.
A boundary line (BL) to be the bottom limit boundary for avoiding crashing into the ground and making resuming flight possible in the event that the aircraft loses altitude is then calculated on the basis of the flight capability of the aircraft.
The height-gathering survival means comprises an envelope, cords, a user harness, a flexible tube, a height-lowering means, and a filling means with a feed valve.