Originally Posted by
maui
Consider these points;
1) If FLCH controls V/s, why then do we need a separate and distinct VS mode. On your reading, they are doing exactly the same thing?
2) Why can you NOT select FLCH and VS modes simultaneously?
1) If FLCH controls V/S, it is the thrust channel doing it. In the VS mode, it is the pitch channel doing it. Not the same redundant thing.
2) Because they do contradictory things - the former controls speed with pitch and the latter controls path with pitch - and vice versa for the thrust channel.
Request for confirmation can run both ways. Can you produce a credible reference for your position that FLCH will calculate and target a specific ROC/ROD in compliance with your assumption of method of operation. Or Vessbots for that matter.
I already did, from
https://www.ameacademy.com/pdf/boein...g-777-FCOM.pdf :
"THR - The autothrottle applies thrust to maintain the vertical speed required by the pitch mode."
Of course it's an overly condensed and vague statement that could mean different things, but a plain reading of it certainly suggests that THR (as part of FLCH) controls vertical speed. And if you think it doesn't, then you're in agreement with me as I wrote in
post 5.
As I reduce or increase the noise and maintain the locked speed, I will constantly monitor the consequential variation in vertical speed and calculate the approximate time to level.
You made a point before about vertical speed being a consequence, and not controlled target, of pitch controlling airspeed. While that is true, it is a physical event in the chain of events all the same. And, if the FCOM quote above is true, then the pitch and thrust channels in FLCH are both resulting in vertical speed changes, which creates the potential for interference as THR responds to it.
Have you missed the memo regarding this being a full time AT?
Perhaps I'm just tragically incapable of escaping my faults in thinking carefully about what I read, but his complaint was specifically based on the AT being on full time.