"The FMS is not a complete take-off performance computer" Agreed. And that's an understatement. And if Mr Boeings product liability department saw it touted as such they'd have kittens. That's not to say it can't offer a useful cross-check against SOME parameters; but it's not something which was in the toolbox of the subject AF crew, -or any type I operate and hardly justifies your spiky jibes.