> MCAS is a convenience feature that counteracts the plane's tendency to pitch up more than you want when climbing. It's still controlling control surfaces. >

> MCAS is a convenience feature that counteracts the plane's tendency to pitch up more than you want when climbing. It's still controlling control surfaces. > Sure it can improve safety, so can lane keeping in a car. Neither are critical to operation. You can fly/drive perfectly safely without them so they need not be super hardened against failure because you can just switch them off. I'm not quite sure where to begin. Just because the absence of something would make the plane flight worthy doesn't mean the addition of it keeps the plane flight worthy. Take your lane following example. Sure, they can be turned off, but that didn't help the person whose Tesla ran straight into a jersey barrier because it got confused by it and where the lane was. (https://www.popularmechanics.com/technology/infrastructure/a21205127/ntsb-teslas-autopilot-steered-into-barrier-in-fatal-crash/ https://www.popularmechanics.com/technology/infrastructure/a...) If a mechanisms can control the vehicle, it is safe critical. It needs to fail safe under all conditions. The requirement to fail safe is part of what makes it a safety critical system. In the most extreme of examples, adding a lane following module to a car that randomly swerves into jersey barriers once at speed and if the barrier is close enough would be a clear example of a situation where the automatic controls can cause a situation that a human could not possibly react to; hence, the system itself needs to be held to much higher standards.