When this is done badly, we end up with the 737Max.....
Turns out that the 737MAX didn't have (working) backup systems. And now they have tried to implement one, they are getting strange system crashes (that would ultimately lead to a plane crash).
It's truly bizarre that the MAX's flight computers only look at one angle of attack sensor, when there are clearly two fitted to the aircraft...unless the other one only talks to the MCAS system...
In any event, it's clear to anyone with eyes and an engaged brain that the problem with the MAX isn't a software issue. The problem is with MCAS itself, or rather the reason it was put in in the first place. It's a hack job, pure and simple, because the alternative was to significantly modify the airframe (an FAA major mod), far better to develop some software (MCAS), sell it to the FAA as a minor mod that marginally improves flight characteristics and save a boatload of cash upfront.
Then blame the pilots when your flawed plane hits the deck.