Hi, thanks for your input. I don’t wish to contradict you, but in what mode does thrust control altitude?
It's not desirable, but let's say you descend using FLCH: pitch controls speed, AT goes to IDLE then THR HOLD allowing you to adjust the thrust levers to control RoD. If you add too much power you'll actually stop the descent, and you're inadvertently controlling altitude with thrust. Add even more power and you'll actually start to climb even though it was supposed to be a descent, and with no MCP altitude to ALT CAP on, it'll keep going until it finds its equilibrium Altitude.
It manifests itself in the SIM on single engine work. I've seen someone descending, getting close to the platform ALT with manual thrust, pitch for speed. They noticed the speed was a little low and added power but it hadn't yet alt capped - so all that did was arrest the descent. When they saw that the speed hang changed, they added more power and started to climb. 🤦♂️