View Full Version : Understanding FL CH in FCOM 2
extricate
9th Mar 2018, 14:26
Hi,
Pertaining to Go-Around and having selected FL CH after acceleration height on climb to a certain altitude.
1) How does the system know when to change to climb thrust having gone around and selected FL CH after acceleration height?
Intruder
9th Mar 2018, 18:07
FLCH is a vertical mode that also affects the autothrottles [Boeing]. They will go to the THRUST mode as soon as you select FLCH.
rudestuff
9th Mar 2018, 18:44
I assume it knows because you press the climb button then FLCH?
extricate
10th Mar 2018, 00:48
For B777.
This pertains to go-around. Assuming I went around with Toga (Pressed once), 1000ft, i'll start accelerating by winding up the speed and cleaning up the aircraft accordingly. Once flaps are up, when I press FL CH, thrust will change from GA to CLB. How does the system know when to change to CLB? Is it by flaps settings? As per takeoff sequence?
extricate
10th Mar 2018, 00:49
I assume it knows because you press the climb button then FLCH?
I didn't press the clb button prior to FL CH
Artisan
10th Mar 2018, 04:54
The thrust is scheduled by the Autothrottle/ Thrust mode logic.
When you push the TO/GA buttons, the Autothrottle engages in ‘GA’ mode, in this mode, the first push of the buttons gives reduced go around thrust to achieve 1000-2000fpm. The second push gives full go around thrust.
Engaging level change during a climb, causes the Autothrottle mode to change to ‘N1’. The N1 mode is programmed to schedule CLB thrust.
wiggy
10th Mar 2018, 05:21
For B777.
This pertains to go-around. Assuming I went around with Toga (Pressed once), 1000ft, i'll start accelerating by winding up the speed and cleaning up the aircraft accordingly. Once flaps are up, when I press FL CH, thrust will change from GA to CLB. How does the system know when to change to CLB? Is it by flaps settings? As per takeoff sequence?
What other thrust setting would you think would be appropriate given you have selected FLCH and have deliberately taken the thrust and pitch part of the autoflight system out of go around mode?
In your scenario above AA you are now simply asking the system to perform a “standard” FLCH climb where the thrust is metered to try and get you to the required altitude (as set in the MCP) in two minutes...or if it can’t achieve that rate of climb because of the magnitude of the climb the auto thrust will set full climb thrust.
I’m pretty sure the flap position is irrelevant....
extricate
10th Mar 2018, 05:48
What other thrust setting would you think would be appropriate given you have selected FLCH and have deliberately taken the thrust and pitch part of the autoflight system out of go around mode?
In your scenario above AA you are now simply asking the system to perform a “standard” FLCH climb where the thrust is metered to try and get you to the required altitude (as set in the MCP) in two minutes...or if it can’t achieve that rate of climb because of the magnitude of the climb the auto thrust will set full climb thrust.
I’m pretty sure the flap position is irrelevant....
That makes sense. Could'nt think of other thrust settings other than Clb thrust since I've taken it out of GA thrust. Thanks