And to answer itzly's comment below, NO ONE (that expects to walk away) is going to be landing a passenger airliner in "terrain"
Depends on what you call "terrain". Not so long ago, US 1549 made a successful landing in Hudson River. Would you want the computer to prevent that ? If not, how are you going to stop a suicidal pilot to hit a bridge support instead ?
The point is that with current state of technology, it's better to trust the judgement of an experienced pilot than a computer system. Look at Turkish Airlines 1951 for instance. The computer messed up and landed the plane a mile north of the runway due to faulty radio altimeter, killing 9 people on board. Mechanical problems are still more common than suicidal pilots.
Both good points. I'm not sure we are at the point in autopilot design that could have fully "understood" US1549's dilemma, other than the fact that I think there were several warning alarms going off in the cockpit (like engine failure, stall warning, and icing warning) PRIOR to when the Pilot would have "requested" the autopilot to disengage. I think that even now, that autopilot software could be written to allow manual control in that situation, without exposing too many cases where a rogue Pilot could set-up those kinds of conditions PRIOR to disengaging the autopilot.
And, OTOH, I very much doubt that, other than the low-altitude and proximity-alarms, that there was much that the Germanwing's avionics was upset about even seconds before the co-Pilot screwed the pooch... Maybe I'm wrong; but I still think that even a fairly primitive system could tell the difference between a pilot attempting to regain control of an aircraft that was in distress from a pilot that was simply trying to drive into a mountain.... Or a skyscraper.
As for the Turkish Airlines flight, I DO think that GPS and inertial-guidance-assisted positioning, coupled with on-board mapping, even of the "Car Navigation Computer" quality, could have prevented THAT tragedy. IOW, the computer should have had some "redundancy" in its position-determination software. That one COULD have been avoided without having to graft a homing-pigeon-brain into the autopilot!