Some of them are quite serious (such as dual FMC failures in the case of the 777), and could have been catastrophic if there hadn't been a flight crew there to take over and fly the aircraft manually.
Wheels up, I'm repeating myself here, but the 777 FMC is designed to "fail passive" and give the pilots control. For obvious reasons, that wouldn't be the case with systems designed for a pilotless aircraft.
Also, the FADEC and FBW computers are "Design Assurance Level (DAL) "A". That means flight critical - a significant s/w error is considered to be potentially catastrophic (e.g. unilaterally surging or shutting down the engines, or commanding a dive into the ground). Yes, we still find errors in the implementation, but to the best of my knowledge a DAL A system has never been identified as the cause of a crash.
The 777 FMC is
not a DAL "A" system. It is designed and certified to a lower level - a level that assumes if it screws up the pilots can and will take corrective action (granted, not always a valid assumption).
Also, the 777 systems were designed over 20 years ago. Ancient in electronic terms (compare a 1992 cell phone to one of today's smart phones). In fact one of the larger challenges that Boeing faces today is sourcing those 20 year old electronic components to keep building airplanes.
As I said before, electronics are advancing at an exponential rate. Same thing with s/w development. FADEC s/w isn't people entering lines of code (hasn't been for a long time) - it's people laying out 'flow diagrams' of how the want the s/w to work. Highly specialized automated programs then turn those diagrams into code - which is then exhaustively tested to make sure it functions as intended.
As Tourist pointed out, a pilotless airplane doesn't necessarily need to be perfect, it just needs to better than an all too flawed human pilot.
When SLF are routinely riding to the airport in automated cars that have an accident/fatality rate orders of magnitude better what us flawed human drivers can accomplish today, just how many CFTs, or 777 crashing into a seawall because the human pilot couldn't be bothered to monitor airspeed, do you think they'd be willing to tolerate?
It won't happen this decade, it may not happen during my lifetime (and I expect another 40 years, minimum
). But it will happen.
BTW, those of you noting the Star Ship Enterprise has human pilots, you do know that's science
fiction 