When I was working on my instrument rating, my instructor put me in an old 6-pack kind of simulator and proceeded to fail practically everything.  I forget what I had left: cdi + dg + alt?  ...and med turbulence.

He watched me quietly as I struggled for several minutes and finally augured in. I was furious at my inability to control the plane.   "What should I have done?" I questioned.  
"Nothing.   You're toast with that much broken." he pronounced.

You can talk about statistics all day long but nothing quite captures the situation like sitting there for MINUTES knowing you are going to die and not being able to do anything about it.  


Since then, all my airplanes have a backup AI powered by something different (e.g. vac vs. electric) than the main AI.

Colyn