In that case what happens when the Captain needs a physiological break during the say 8 hour cruise? What if they think they can't leave the seat and as a result become incapacitated?
- then they would be big plonkers, Rodney, who had not read the Ops Manual. This 'need' is covered (in my experience anyway) - and STRICTLY controlled - by company Ops Manuals. What these manuals do NOT 'cover' or 'control' is placing an unqualified pilot in your seat and 'flying' (as part of the constituted crew) from the jump seat! (Well, mine never did, anyway?)