[EddieCPU]

"Underestimating the dangers of designing a protection system"

https://www.youtube.com/watch?v=PlaMQBEg-9M

“In the course of the investigation, a new type of flight assistance system known as the Maneuvering Characteristics Augmentation System (MCAS) came to light. It was intended to bring the flight characteristics of the latest (and fourth) generation of Boeing's best-selling 737 airliner, the "MAX", in line with certification criteria. The issue that the system was designed to address was relatively mild. A little software routine was added to an existing computer to add nose-down trim in situations of higher angles of attack, to counteract the nose-up aerodynamic moment of the new, much larger, and forward-mounted engine nacelles.”

“Apparently the risk assessment for this system was not commensurate with its possible effects on aircraft behaviour and subsequently a very odd (to a safety engineer's eyes) system design was chosen, using a single non-redundant sensor input to initiate movement of the horizontal stabiliser, the largest and most powerful flight control surface. At extreme deflections, the effects of this flight control surface cannot be overcome by the primary flight controls (elevators) or the manual actuation of the trim system. In consequence, the aircraft enters an accelerated nose-down dive, which further increases the control forces required to overcome its effects.”