Bump for this thread, I had this exact same problem. Have flown hundreds of flights without issue, I believe that the problem was caused as someone mentioned earlier, because I changed the step climbs on the init page after getting some updated weather and fuel figures.

 

The aircraft would not obey the MCP altitude no matter what. I ended up cancelling the flight and diverting shortly after I reached FL300 because the autopilot was misbehaving too badly.

 

I want to chalk this up to user error but it looks suspiciously like a bug.

 

James Burke

 

 

The aircraft would not obey the MCP altitude no matter what

You can dial in whatever into the MCP but if the PROF mode is active the plane will stay on profile as commanded by the FMS. As a general rule, changes in the MCP altitude window has no effect on the plane when in PROF mode.

 

 

but it looks suspiciously like a bug.

 

If it were, you'd see a lot more of it here on the forum, yet this is not the case.

Okay, I think I have tracked down the issue, at least partially.

 

The inability to hold/obey altitude commands seems to have been a controller issue that ONLY affects the MD-11, for some reason it was not registering my yoke as centered. It must have been a very very small centering error. In any case I increased the PMDG deadzone and disabled yoke movement AP override and it seems to be OK, for now. I will carefully monitor this in future flights though.

James Burke