But only the qualified pilot can legal fly the aeroplane under IFR unless undergoing instruction
Where does it say so? Leaving aside the old IFR but in VMC chestnut, obviously the aircraft should only be in IMC with an instrument qualified pilot on board, but I dont see that the instrument qualified pilot is not entitled to let the non instrument qualified pilot "steer" without him being under instruction?
With regards to this and the earlier case I am not sure that the "qualified" pilot by definition must "carry the can". I think the can carrier needs the service of a good barrister.
Two pilots set off together and clearly agree that pilot A is PIC. Pilot A enters IMC, but is not qualified to do so, and there is an accident. Pilot B is instrument qualified but didnt know pilot A wasnt. It would be quite ridiculous for pilot B to be liable, any more than if it turned out pilot A's medical or license had expired. The key would be whether or not it could be demonstrated who was in command, or who was most likely to have been in command. Obviously this could prove difficult if both pilots disagreed as to who was in command, or they died. However, while not conclusive, who was in the LHS would be significant. Were I the judge if the charge was the pilot in the RHS was in command I would want to see some reasonable evidence that the RHS pilot was accustom to flying the aircraft from the RHS and some reason as to why he was so seated (assuming of course this was not a student instructor scenario). On the whole it is rare for RHS command in private flights however it might be so argued retrospectively and almost always in my experience the pilots would have had some good reason for the RHS pilot being in command if that is what they had itended.
If you find yourself in command in the RHS then make the arrangement very clear and be prepared to "carry the can" if anything goes wrong. If you are in the LHS and think you are not in command make very certain the other pilot knows he is in command and is qualified to be so.