737-800 FMC - Cutback & Thrust Bump
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737-800 FMC - Cutback & Thrust Bump
I have some questions regarding the 737-800 FMC.
Can anyone explain what Cutback is? Is this an airline specific option?
What are the differences between "Bump Option" and "Full-Rate Option" when selecting takeoff thrust bump?
When using an assumed temperature takeoff, why is this displayed as D-TO on the MFD, while a derated power setting is displayed as R-TO? Wouldn't it make more sense for this to be the other way around? What does the 'D' signify?
Can anyone explain what Cutback is? Is this an airline specific option?
What are the differences between "Bump Option" and "Full-Rate Option" when selecting takeoff thrust bump?
When using an assumed temperature takeoff, why is this displayed as D-TO on the MFD, while a derated power setting is displayed as R-TO? Wouldn't it make more sense for this to be the other way around? What does the 'D' signify?
Cutback: Is part of the Boeing Quiet Climb System. Never seen it anywhere in real life but it is apparently a noise abatement option.
Aero 21 - Quiet Climb
My guess on the 2 next ones is,
"Bump Option" You can bump TO thrust to 27K (no assumed temp avail) the few times its needed. (cheap option) default thrust is 26K
"Full-Rate Option" Default thrust is 27K, can use assumed temp and derate to 26K or 24K (expensive option)
Aero 21 - Quiet Climb
My guess on the 2 next ones is,
"Bump Option" You can bump TO thrust to 27K (no assumed temp avail) the few times its needed. (cheap option) default thrust is 26K
"Full-Rate Option" Default thrust is 27K, can use assumed temp and derate to 26K or 24K (expensive option)
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Full rate refers to the thrust selection in the FMC N1/LIMIT page for T/O thrust, either 26K or 27K depending on the engine rating.
"T/O Bump" is I think old terminology for a 27K T/O. In the latest FMC, to acheive the same thing you just select 27K option in the N1 LIMIT page.
Regardless, after T/O the amber N1 bug reduces back from 27K N1 to 26K and remains 26K N1 for the remainder of the flight.
However, even with a 26K engine, fire-walling the throttles past the amber bug gives 27.3K.
So in summary, all engines are 26K, except that some can be rated for 27K for T/O only.
"T/O Bump" is I think old terminology for a 27K T/O. In the latest FMC, to acheive the same thing you just select 27K option in the N1 LIMIT page.
Regardless, after T/O the amber N1 bug reduces back from 27K N1 to 26K and remains 26K N1 for the remainder of the flight.
However, even with a 26K engine, fire-walling the throttles past the amber bug gives 27.3K.
So in summary, all engines are 26K, except that some can be rated for 27K for T/O only.
Last edited by Sciolistes; 10th Jan 2013 at 15:35.
