SNS3Guppy:
That's what the crew in American Airlines #965 thought, too. Lots of redundancy, a solid data base, enter the information, and you're good to go. At least a little way.
.......
Too many "children of the magenta line" today that think they have a FMS/FMC, and they're golden. The crew of Flight 965 was golden, too. Now, of course, they're dead.
The phrase "errant blunder" describes the result of the most grossly inept actions of the AAL 965 crew. Historically, in the design of nav aids and instrument flight procedures it has never been possible to protect against gross errors by flight crews.
Having said that, had that horribly inattentive, disoriented (unoriented?) crew had 3-D synthetic vision integrated with EGPWS/TAWS there is a good chance they would have seen the situation in sufficient time to have prevented the crash.
They descended through a lot of beneign, but unprotected black air before they gradually came upon relatively forgiving terrain (compared to other terrain further away).