De-Rate vs Assumed Temperature
Hi Fredairstair. I am not able to compare the "De-Rate" method I used to use against the "Assumed Temperature" method as I have never used the latter. Reading other posts I think I would rather use the old fashioned "De-Rate" method I used, in as much that having determined the thrust required, for the conditions and runway length available, to safely take-off at a given BRW it was simply a setting of the "De-rated" thrust determined with the thrust levers. If for any reason whatsoever extra thrust was felt required, max thrust (up to flat rated thrust up to 29C) could be applied by simply advancing the thrust levers. No presetting of FADEC or engine components came into it. We had a maximum of three levels of "De-Rate" and it could be used at all our ports with the exception of 07/25 at Sydney and at Gatwick. We also had a "Bump Thrust" available, if required, to get us out at weights above those to which we would be limited with normal Max thrust.
I am sure there are some variations between respective methods, however they are all aimed at achieving as long between engine overhauls as is possible.