I'm wondering whether it might be feasible to develop a system that causes a plane to automatically descend to something like 5000ft
This was mentioned elsewhere ( probably the other thread) - such a system would have to be tied into a Terrain database since in many parts of the world descending to FL50 will put you under the ground (10000' amsl won't give you clearance in parts of Europe and the States, in some parts of the world even 15000' won't do).
FWIW I've "enjoyed"
similar training to that fireflybob describes - I agree entirely with his post.