hey pilotchute...
Don't get confused between 'derated power' and 'assumed temperature power', they are two different things!
With derated power, the FMC commands a set decrease in N1 RPM that usually equates to 10% (derate 1) and 20% (derate 2), with an accompanying decreased selection for climb power, (1 & 2) since you don't want to have climb power set at a level greater than takeoff power!
With assumed temperature power, you select a temperature greater than the actual ambient for the takeoff conditions, and the engines simply produce the output equivalent to that temperature, even though no actual temperature increase is felt by the engines. This is simply an alternative way to decrease the takeoff power to preserve the engines. Any decrease in takeoff EGT will extend the life of the engine! This input temperature is selected from examination of the takeoff performance of this airplane at this runway, its not random!
I am not aware of any baro input to this performance calculation, I've never ever seen that done!
As regards 'flat rated power', if an engine is flat rated to ISA+15, then that engine can maintain its rated power output up to ISA+15 degC, (at sea level) with any further increase in temperature resulting in a (usually) linear decrease in power output.
Cheers, EW73
Last edited by EW73; 22nd June 2012 at 09:47.