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TO1 / TO2 with assumend temperature

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Guest topcat

Hello forum readers,I have a technical question about the 747-400:Is it allowed to make a derated (TO1 or TO2) in combination with an assumed temperature take-off.I know Airbus does not allow a derated/assumed combination. I don't know if Boeing does.Any clues?

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I am pretty sure some carriers do this. I am not sure where I was reading it, but someone from Singapore Airlines says that they use TO1 (fixed derate) in combination with an assumed temp. with their 747-400 series.So I imagine it is allowed.Hope this helpsRudy.

Rudy Fidao

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As far as the NG goes you can derate and use an assumed temperature thrust limit. But you have to be very careful when doing so. See the below page for some discussion:http://www.b737.org.uk/assumedtemp.htmEspecially look at bullet 2 second paragraph:8<---A temporary form of de-rating known as a "T/O de-rate" is accessible through the FMC on TAKEOFF REF 2/2 or N1 LIMIT (NG's) but this is prohibited by some operators. The T/O de-rates (TO-1 & TO-2) can be 10 to 20%. It follows that an engine may be de-rated and also be using reduced thrust in which case you could be taking off at Full power -20% -25% = 60% of the full power of the engine - scary thought! Note that a T/O de-rate can overridden by firewalling the thrust levers; this action will give the thrust rating shown on the IDENT page.8<---The above will give you a clue as to wy some airlines don't allow derate and assumed temp thrust limit at the same time. 8-OCheers,

Mats Johansson
PMDG Flight Test Dept

| Asus Z270-A | Intel i5-7600K @ 4.8 GHz OC/H2O | nVidia Geforce GTX 1070 8GB OC/O2|

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I have personally witnessed from the jumpseat a combination of assumed temperature and derate. If I recall specifically, according to the analysis charts we took off using a TO2 with an assumed temp of 55. That's a lot of derate but we were on a 12,000 ft sea-level runway on optimal conditions and very light load. It doesn't get any better than this for a takeoff. It was a 777-200, but I'm pretty sure osme 747 carriers perform combination takeoffs as wellBest Regards,Victor Limahttp://www.precisionmanuals.com/images/forum/800driver.jpg

Victor M. Lima

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