pilotchute
22nd Jun 2012, 05:44
Hello,
I have a interview soon with a major carrier but don't have any jet time. I was just wondering what is entered into the flight management system for a de rated thrust take off? I thought it was temperature but I have been told also that its pressure height. Which ever one it is would it be a higher value that is entered? If it is how does that produce less thrust?
Also another question is what is meant by the CFM 56 is flat rated at ISA +15?
Thank you,
flame_bringer
22nd Jun 2012, 06:07
Never heard about entering the barometric altitude in the FMS, I know of the flexible tempreture which the pilot enters to reduce the take off thrust at FLX MCT detent to increase engine life.
Flexible tempreture must always be higher than what the tempreture actually is except in hot and high conditions when it has to be the same.
It means engine power rating is reduced at international standard atmospheric temperature 15+.
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
pilotchute
24th Jun 2012, 11:06
Cheers for the very informative answers. I appreciate the time you put in. Let you know how it goes.