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T/O thrust on B777

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T/O thrust on B777

Old 25th Jun 2013, 07:28
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T/O thrust on B777

I am puzzled by the B777 T/O thrust vs Climb thrust question...

On the last 2 occasions that I have flown with a major carrier on the B777 (with a full load of pax and 7 hr sector lengths), at acceleration altitude, Climb Thrust has resulted in an INCREASE in thrust...

My understanding is that de-rated Take Off thrust should never be less that Climb Thrust???

Can an Op please explain...Is this a normal performance practice on the B777?
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Old 25th Jun 2013, 08:45
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One theory is that many airlines do double derate...10 /20 percent and use an assumed temp method.....quite a low thrust setting but as 777 has big engines it is adequate for most situations.
I know of one airline that recommends using full climb thrust at 800 feet or whatever the altitude is for that airport. They say it will improve engine life by more quickly climbing above lower atmosphere normally full of sand( think Middle East ).
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Old 25th Jun 2013, 09:37
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Correct for the old gen aircraft, but the 777er is a bit different.
Older aircraft, or should I say, those with smaller engines, are limited to 25% thrust reduction for T/O and so with the max clmb debate being 20%, this normally resulted in a pwr decrease at thrust reduction alt.
However, the ER derate on T/O is up to 40%, so with a 20% derated Clmb, a pwr increase results.
Not always, but at anything but a near limiting T/O
Also, To save fuel, some operators are removing the Clmb derate at anything over MLW, so pwr increases to full Clmb.
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Old 25th Jun 2013, 13:57
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Thanks 'singleseater'!

That is what a mate of mine surmised! Happy as a pax now!
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Old 25th Jun 2013, 13:59
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... Next flight you need to ask him why he did that & why he did it without brief you as it indicates a big gap in his CRM...

Mate, I was just a pax!
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Old 25th Jun 2013, 14:30
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With assumed temperature the max thrust reduction is 25%, so you basically takeoff with climb thrust already. If you have the option TO-1 or To-2 you would takeoff with 10 or 20% of T/O thrust, in addition to that you could use assumed temperature method (tables provided for that) which could make you takeoff with a total thrust reduction of more tan 25%, at thrust reduction altitude you have the option to continue with CLB 1 or CLB 2, which has almost no effect on engine life, but on fuel consumption++, if you select CLB thrust the engines would spool up to the 25% of the full T/O thrust which can be quite a push.
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