Method and device for automatically protecting an aircraft against an excessive descent rate

A method for automatically protecting an aircraft against an excessive descent rate, the method comprising the following string of successive operations:

• a) measuring with a set of information sources a current vertical speed and a current height of the aircraft with respect to the ground, referred to as current flight parameters, and measuring with a different set of information sources independent from the set of information sources a current auxiliary vertical speed and a current auxiliary height of the aircraft with respect to the ground, referred to as current auxiliary flight parameters;
• b) comparing with a comparing device these current flight parameters with at least one flight envelope, referred to as a safety envelope, depending on an unauthorized flight envelope, the unauthorized flight envelope defining couples of vertical speed and height, illustrating an excessive descent rate and that are not authorized for the aircraft, and separately and independently comparing the current auxiliary flight parameters with at least one auxiliary safety envelope such that comparing the current flight parameters with the at least one safety envelope is performed independently from comparing the current auxiliary flight parameters with the at least one auxiliary safety envelope, and triggering a protection only at least if simultaneously:
• the current flight parameters are located in the safety envelope;
• and
• the current auxiliary flight parameters are located in the auxiliary safety envelope;
• and
• c) should the protection be triggered:
• generating protecting orders automatically upon the triggering with a calculation unit for controlling the control surfaces of the aircraft acting on the current vertical speed, the protecting orders configured to cause the aircraft to avoid being located in the unauthorized flight envelope;
• and
• applying the protecting orders automatically upon generation of the protecting orders with a surface operating device to the control surfaces and without requiring added actions or workload for a crew of the aircraft.