I'm still a little alarmed that the concept of this trap had never occured to me.
1. I deduce that talk of autothrottle wakeup in HOLD mode is perhaps misleading as it is already 'awake'- ie: it is already activated in HOLD mode. Maybe this is the crux of why there is no stall protection logic.
2. Could the accident aircraft have been in VNAV SPD with 0' or a MAA set on the MCP?
"Note: During a descent in VNAV SPD, the autothrottle may activate in HOLD mode and will not support stall protection"
3. Am I correct in saying that if there is no altitude set on the MCP for FLCH to capture you effectively have no autothrottle? And that the only way to regain the autothrottle is to change modes or turn the f/ds off, whereby the autothrottle mode changes to SPD?
The sad thing is, the A/T is virtually identical the 757/767, and almost all the little traps existed when I flew that as well. All these traps were demonstrated when I did my 757 course 12 years ago, by experienced trainers with many many years of TRI/TRE experience.
Sadly inspite of the inevitable well meaning protestations of a few, my 777 course lacked the depth of understanding to even delve close to the depth I encountered previously, the net result being a lower level of systems knowledge.
I pity the guys who continue to baffle themselves in the hold using VNAV who scratch their heads when the thing decides to climb....
It must be a real shock for an aeerboos convert.