If it is company policy that there are to be no flight deck visits in flight then NO-ONE but crew members visit the flight deck. Not difficult, is it?
I once had a captain fly a non SOP approach. ISTR saying "Well YOU'RE the captain!" Thought the tvat might get the message.
Next time it was "Captain! You are high and fast on a short wet runway!"
The prat landed and burst all the maingear tyres. Still, better than going off the end.
