Even more interesting when your co-pilot does not understand English and you have an interpreter in the jump seat. One of the principles of training is that when he is projecting you all to certain destruction you have to let him carry on so far to see whether he is going to correct himself. Should that not happen then you have to initiate command responsibility.
There are three ways.
1. Take over control and tell him where he has gone wrong. The interpreter will not understand the technical reasons so your co-pilot will suffer a massive loss of face because you have overruled him.
2 Tell the interpreter to tell the co-pilot what actions to take to correct the situation. This will end up in an argument between the interpreter and the pilot as to what I was talking about.
3 The final and best way. Convey to the pilot by means of the interpreter suggestions in such a way that the pilot thinks that they are his idea, in which case he will implement them. Face is saved all round and everybody comes home and Gam Beis at a big company dinner.
The world can be so different elsewhere.