Enhanced Stall Warning design and integration in the Airbus A320 family Auto Flight System

The Auto Flight System (AFS) is the Airbus avionic system in charge to manage and guide the aircraft during its automatic flights. The AFS does not replace human operators yet; instead it assists them in controlling the aircraft. This allows the crew to focus on broader aspects of operations such as monitoring the trajectory, weather and other systems. The system of automatic flight assists the pilot in flying the aircraft within the normal flight envelope, enhancing safety, optimizing performance, reducing pilot workload (fuel consumption) and decreasing costs. This Master Thesis aims to illustrate how the Enhanced Stall Warning function is implemented in the Auto Flight System in order to deliver to the airlines, aircrafts facing with higher standard of safety and reliability. As an external member of the Airbus Design Office, my activities during the course of this thesis were focused on the Enhanced Stall Warning (ESW) function development. Airbus started improving its stall warning system with feasibility studies, after the catastrophic accident during the flight AF447 the 1st June 2009 that involved an A330-203 and it provokes the total loss of the aircraft and of all the 228 cabin occupants. Translating the high level aircraft requirements into low level system requirements, the implementation of the Enhanced Stall Warning system carries out a more robust, reliable and available system with respect to the legacy version which is flying on the on-service Airbus aircrafts. The improvements come from the recent UAMM update (Unreliable Airspeeds Mitigation Means) and the fact that the new stall warning version will consider both the ADC and IRS angles of attack and the speeds in order to trigger the stall aural and message alarm only in case of reliable stall warning avoiding the activation of spurious alarms. Cross-check monitoring was implemented in order to consolidate function data avoiding every false autopilot disconnection. This project gets into a wider field with the aim to widen the autopilot authority even in case of multiple failures. Further evolution of the function will be considered in this master thesis up to the introduction in the cockpit of a new pilot interface that allows the crew to monitor in every situation the aircraft attitude and to display the aircraft marge from the aerodynamic stall. The stall problem is at the state-of-the-art one of the most topical problem in the civil aviation after the two Boeing 737 Max 8 crashes in the last year that provoked the death of more than 340 people (Lion Air Flight 610 and Ethiopian Airlines flight 302). A paragraph is entirely dedicated to the Boeing study case to highlight the Reason’s model which brought the complete Boeing 737 Max 8-9 fleet to be stopped on ground since March 2019 after the two catastrophic accidents that occurred in October 2018 and March 2019. Some consideration will be made and some advices and preventive measures will be given to improve the flight safety since what has been learnt during my experience.