If you have chewbacca pilot card and determination can you discard ship critical cards?

I don't see why you would. Pilots get discarded as per determination, all others get downraded as per chewie.

Since both abilities trigger off of "When you are dealt a faceup Damage card", you get to choose the order in which the abilities resolve. Naturally, as Vonpenguin said, if the card has the Pilot trait you would use Determination to discard it. If it has the Ship trait then Determination cannot be used to discard it, so you just flip it without resolving the card text as per Chewbacca's ability, and it becomes a "normal" damage card.

i though chewie ability mean no crits were possible at all so all face up damage cards go face down regardless of ship or pilot

DarkGuard said:

You need to read the rules more closely, not just rely on mental shortcuts.

Chewbacca: When you are dealt a faceup Damage card, immediately flip it facedown (without resolving its ability)

Determination: When you are dealt a faceup Damage card with the PILOT trait, discard it immediately without resolving its effect.

And, as stated above, since both abilities are trigged by the same word-for-word condition, you choose which takes effect first. Myself, I'd rather discard it entirely rather than have another point of damage.

Yeah, chewie doesn't discard crits, just flips them face down, you still take the damage. Determination actually discards PILOT crits entirely, thus you don't take any damage from them.