757 auto throttle logic
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757 auto throttle logic
One thing that I've wondered about for awhile:
Descending using FLCH, the throttle goes to idle. In the descend, select VS mode and speed bugged down, the auto throttle goes from fully idle to adding a little power (though still less than idle with engine AI on).
Anyone know the logic behind this? A quick scroll through the FCOM didn't provide the answer...
Descending using FLCH, the throttle goes to idle. In the descend, select VS mode and speed bugged down, the auto throttle goes from fully idle to adding a little power (though still less than idle with engine AI on).
Anyone know the logic behind this? A quick scroll through the FCOM didn't provide the answer...
One thing that I've wondered about for awhile:
Descending using FLCH, the throttle goes to idle. In the descend, select VS mode and speed bugged down, the auto throttle goes from fully idle to adding a little power (though still less than idle with engine AI on).
Anyone know the logic behind this? A quick scroll through the FCOM didn't provide the answer...
Descending using FLCH, the throttle goes to idle. In the descend, select VS mode and speed bugged down, the auto throttle goes from fully idle to adding a little power (though still less than idle with engine AI on).
Anyone know the logic behind this? A quick scroll through the FCOM didn't provide the answer...
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Anyone know the logic behind this?
In FLCH, AT it is programmed to give either Climb or Idle and it does not expect to change until approaching the level set.
In VS + speed mode you might change the rate unexpectedly so the engines are set to respond quicker (higher idle).
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Mr Ocean,
Based upon what theory do you make the statement "757 autothrottle is a poor system"?.Ive been flying it for 14,000 hours on type now (still do) and havent had any issues with it.Peter.
Based upon what theory do you make the statement "757 autothrottle is a poor system"?.Ive been flying it for 14,000 hours on type now (still do) and havent had any issues with it.Peter.
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Opinion: I don't like the 757 autothrottle system.
Factual statement (i.e, not opinion): The 757 autothrottle is a poor system.
The second statement deserves some kind of back up information such as, why is it bad? What does it do poorly that other systems do well? What is an example of a good system? Not just "that's my opinion."
Factual statement (i.e, not opinion): The 757 autothrottle is a poor system.
The second statement deserves some kind of back up information such as, why is it bad? What does it do poorly that other systems do well? What is an example of a good system? Not just "that's my opinion."
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. Factual statement (i.e, not opinion): The 757 autothrottle is a poor system.
It does the job.
Spent a few years on the 757 and never paid much attention to the A/T.
Guess it works the way it was designed to do.
Certified for CAT III approaches.
What else do you want it to do?
Mr Ocean,
Based upon what theory do you make the statement "757 autothrottle is a poor system"?.Ive been flying it for 14,000 hours on type now (still do) and havent had any issues with it.Peter.
Based upon what theory do you make the statement "757 autothrottle is a poor system"?.Ive been flying it for 14,000 hours on type now (still do) and havent had any issues with it.Peter.
It is poor in the respect that it is very slow reacting to airspeed changes
Thanks tdracer. Always nice to know the "why's". Still don't understand while Boeing never offered an upgrade to the system, our latest757s were built in 2001/2002 IIRC and the JT9D was long gone out of the production system at that time.
True, but the avionic software needs to be downward compatible - so they may well have updated the s/w but it still had to work on the JT9D.
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757 and 767 are the first of the "4th Generation" of jet transports, which the latest airbus and Boeing models all belong to as well.......but im sure you already know this fact.
Although the 757/767 series had a major FMS change with the advent of the Pegasus, the fundamental aspects are a design circa 1980.
757 and 767 are the first of the "4th Generation" of jet transports, which the latest airbus and Boeing models all belong to as well.......but im sure you already know this fact.
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Goldenrivett
Actually FLCH is more clever than that. It utilises a time target of 120 secs to achieve required level change and adjust thrust to so do. i.e. increases/reduces sufficient thrust as required-just as a pilot would. If it cannot achieve that then it sets CLB or IDLE as required. This is particularly evident when being stepped down 500 ft or so by ATC during intermediate approach. Of course you simply manually override if its not doing it quickly enough.
Mind you this was a 100 or so years ago (80s-90s) and reading the various comments above, its just possible that's changed but I think unlikely.
In FLCH, AT it is programmed to give either Climb or Idle and it does not expect to change until approaching the level set.
Mind you this was a 100 or so years ago (80s-90s) and reading the various comments above, its just possible that's changed but I think unlikely.