Just to raise a topic of discussion.
Being the Captain the ultimate responsible for the safety of the flight can he/she refuse to take off with a FO which he/she deem not sufficiently proficient on the type?
Personal experience :
First assignement I got once ckecked out on the 777 was to sit in the left seat in the sim for a F/O who was just coming back from part time leave if I recall.
Simple enough, it was supposed to take an hour with 3 engine failures between V1 and VR: three times in a row..............we crashed up to the point where the intructor decided it was the sim that wasn't working properly !!!!!! and triggered the engine failure after gear retraction. We barely barely made it and I thought we were in cookoo land.
Sure enough, the F/O was checked and signed and left merry as a lark leaving me with the tought that if I ever see him / her again on my flight, he / she is history. Does that answer the question ?
Question : Why didn't I open my mouth ??? That's the trick, because if you do.............you're toast !!