N1 FLEX vs N1 REDU
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Hello,
There are 3 take-off thrust settings.
N1 REF (non-flex / max thrust setting)
N1 FLEX
N1 REDUBoth N1 REDU and N1 FLEX involves selecting TO REDU on the TRP and setting a temperature.
The difference is that N1 REDU uses a fixed standard temperature for a given pressure altitude and ambient temperature (and bleed config etc...).
N1 FLEX could be any temperature between the ambient temperature and +50C as long as the thermodynamic limits and aircraft performance allow for the given FLEX temperature to be used.My understanding of the TO REDU mode is that it reduces the thrust even further than the reduction you would get from just setting a higher temperature.
The point of that is that when you set a higher temperature, you still get better performance (and higher thrust?) from the aircraft than if the ambient temperature was actually the given FLEX temperature.My question is when would you choose N1 REDU instead of N1 FLEX?
I have tried to find an answer to this in the FCOMs and SOPs but haven't been successful.
I assume that this knowledge is passed from pilot to pilot and is possibly an experience thing.Best regards
Johan -
TO REDU and TO FLEX are essentially the same thing, one just enables the selection of the other. The TRP has two modes that can be used to set takeoff power:
TO MAX: This is the maximum power the engines can provide for takeoff or go-around. This will provide an N1 REF value on the TRP digital display and on the N1 SET display on the PED.
TO REDU: With TO REDU selected, a reduced N1 will be calculated and displayed on the TRP digital display and on the N1 SET display on the PED. If a further reduction in takeoff thrust is required, a flex temperature can be adjusted on the TRP to further decrease the takeoff thrust.
So in an operational sense, TO MAX would be used when you need the maximum performance from the engines during take-off or go-around, TO REDU would be used when a small reduction in thrust is deemed acceptable for the take-off or go-around, and a further flex can be applied to the TO REDU setting in order to fine-tune the amount of thrust that is required.
Hope that helps.
Mark - Just Flight
