Pitch Autotrim

Okay so 15 deg bank is a less than standard rate turn unless you're pretty slow and 0 -500 fpm descent would be expected unless you corrected with back pressure (nose up pitch correction). My advice to anyone trying to figure out so-called autotrim (I really don't like that terminology) is to ignore it. Just fly the airplane like a Cessna, in which you are required to nose up in a turn.

Your advice about ignoring the autotrim system and flying the 777 like a Cessna is very sound. I do the same myself. The point being made was that even up to 30 deg bank the real 777 FBW will maintain the vertical flightpath so no pitch correction should be necessary. Assuming you are stabilised before starting to turn of course. So the natural tendency for the nose to drop doesn't happen. Beyond 30 deg bank it is allowed to.

 

If you make a pitch input inadvertently while applying wheel input then the aircraft will respond of course. Also if there are gusts or turbulence then it won't maintain altitude perfectly either.

 

As long as you keep the aircraft trimmed correctly for the current airspeed then it works well. Display the PMDG optional trim reference speed bug if it helps. Fly with small inputs. The FBW simulation isn't ideal but it works well enough if you respect its limitations.