Autopilot versus Autothrottle
Would it be possible to get dominating or conflicting guidance, navigation or flight control commands due to the mode selection when using these automation/software functions at the same time?
i'm sure the software is under configuration management and control, and should be thoroughly tested and wrung out before updates are pushed out to the fleet, but software can be difficult.
For example in this incident the aircraft is flying at 140 knots in a stabilized approach and crosses IMTOY at the correct 1380 MSL altitude and on the 3.28 constant descent angle. Eleven seconds later it reaches the 1200 MDA (or 1250 D-DA), and the software takes action based upon the dominant mode to throttle back the engines and begin a very steep descent. Five seconds after that the sink rate warning is issued due to the high vertical speed. Everything seems to be working okay according to the software because that is what it is programmed to do. But the dominant mode may have issued a command that conflicts with the best interest of the aircraft's stability or safe operating during final approach.