There are also a couple of traps when using FLCH on a Boeing.
1) If you are descending in FLCH on an approach with say 2000’ in the alt sel window and are approaching that altitude and you then put 4000 feet in the window for the missed approach it will immediately start a climb to that altitude and make you high on profile.
2) If you are descending in FLCH and disconnect the autopilot and raise the nose (ignoring the flight director) the speed will reduce below target speed and the autothrottle will not help you out. Nor will the low speed function of autothrottle wake up
chip in.
The Asiana 777 that crashed at SFO fell into both of the above traps in quick succession. Some people think its a defect in the system that it can happen. I don’t. I think you just have to understand how it works.