Without wanting to sound overly blunt, I sincerely hope you're joking - mistaken FMS entries have caused far too many hull losses and near-misses over the years - the Cali 757, and the Indian and Air Inter A320s just for starters!
I'd agree with you that the FMS mistake was huge in the Cali crash but the Indian Airlines and Air Inter A320 crashes involved incorrect vertical mode selections, not FMS (or FMC) mistakes as I recall.
Still, the format of modern FMS entries is archaic and purely textual, definitely DOS or early IBM style. You get a crossing restriction of FL90 in Europe, is it FL90, FL090, 9000, 90, /090 etc.?
We Americans couldn't correctly call out flight levels below 180 even if our lives depended on it (and maybe they do). We burn hours of sim time doing wacky 'route mods' to try to figure out how to get the FMS to do what we want. A more modern user interface like that found on some corporate aircraft would save lives and cut training costs.
However, I don't think poor FMS programming can explain more than an hour of lost comm over the Lower 48.
Maybe they really just 'lost track of the time' and forgot to descend but that explaination sure does sound fishy.
You can B.S. the fans, but you can't B.S. the players...
