answer09

在国外论坛上看到一个，基本上这个说服我了，unforeseeable是形容weather本身的属性，cannot be foreseen更多指人为原因

'You cannot drink the water' and 'the water is not drinkable' are subtly different. There could be any reason why you cannot drink the water (maybe you have a toothache etc.) - the first sentence does not reflect upon a property of water - it reflects on your inability to drink it
The second one however means that there is something wrong with the water itself, because of which it is undrinkable.
Similar is the case with 'foreseen' and 'foreseeable'.

除了语法规则如that be 罗嗦，原句could不能省之外，可以用语义验证一下：考虑到后面与weather平行的是pilot error，这里的weather或许也暗示人为原因更好。