Engine derate methodology

[Vendeeglobes]

Apologies in advance as I’m sure this has been done to death

Can someone please point me to an article, graph etc detailing methodology for jet engines.

More specifically as to why e.g. a TO1 fixed derate gives a higher thrust (in some cases) than a TO assumed temperature rating.

Many thanks....

[noptawat]

Actually, De-rated & Assumed Temperature (TFLEX) Rating are completely came from a different aspect of view in term of operation :)

๑ 1 Derate Good on Short RWY gives you more MTOW than Full Thrust but you can not apply Full thrust since Vmcg/Vmca = More MTOW = Company HAPPY

๒ 2 FLEX you can still apply TOGA at any phase if needed- contrasted to lateral handling difficulty. It will consumed more fuel then TOGA to reach specified climb gradient but It reduced EGT = Engine Life = Company Happy

[FlyingStone]

Assumed temperature allows you by regulation to reduce thrust by maximum 25% compared to full thrust, whereas manufacturer can decide on derates themselves, and TO-1 is normally 90% of the full rated thrust.

[john_tullamarine]

The advantage of derate on a shorter runway is that the lower rated thrust will be associated with a lower Vmcg/Vmca. This, in turn, permits a lower V1 which is where we derive the advantage. Derate is a bit like unbolting the bigger engine and bolting on a smaller engine .. but easier.

Flex offers some maintenance cost advantages but comes with the full power Vmcg as the pilot is able to use rated thrust should that be considered desirable. However, keep in mind that pushing up to rated thrust from a deep flex might make things more than exciting in the OEI situation. I was involved in an investigation years ago where this probably was very instrumental in the resulting fatal fireball.

[Denti]

And then you can use both at the same time, which makes it even more confusing. In the simulator (never had to do it in the real world) things would go very exciting indeed in a very short amount of time if one advanced thrust levers from a derate 2 and high flex to full thrust... That demonstration usually resulted in not touching the thrust lever of the running engine on the next try, after all take off performance OEI is calculated on the used thrust level.

[Dave Therhino]

There's an FAA advisory circular (AC 25-13) about derate and reduced thrust that might be helpful to the OP:

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/4b385bb9e4e9c4da862569d00076acf7/$FILE/AC%2025-13.pdf