Turning into a good discussion ...
So, unless you are limited by climb/2nd segment, ATM method will give you zero (or almost zero) stop margin, regardless of the weight you’re taking off at.
QF was one of the first to introduce reduced thrust. The then Performance Boss, Wal Stack (with a flying background in prior years), sold the idea to the troops with the guarantee that he would always make sure that there was a runway pad left in the kitty for Mum and the kids (1000ft, if I recall correctly). A wise old chap was our Wal and a thoroughly entertaining lecturer - he was a visiting lecturer at Sydney Uni when I were a young lad student there.
With flex you get max rated on the live engine so more yaw and control probs with a failure.
Only if you elect to shove the throttles up in the event of a loss of noise.
my belief is squarely due to the fact that pilot performance training morphed from actual Aircraft Performance to demonstration of
Indeed. Back in the 60s-80s the ops engineers ran the performance and weight control courses for endorsements and a fair bit more of the underlying stuff was passed across. I provided that for one operator during the 70s-80s and their line pilots got to know a lot more than the typical pilot has at the end of his ATPL exams ....
some of the installations cannot be firewalled beyond the operational DRT setting (major good)
.. but those that can present an ever-present worry to management and regulators.
Lower Vmcg/a does not explain it, because the DRT operates inside its limit and so does the AST.
Handling may provide some useful outcomes but engine life cycle dollar costs are what it's all about.
Derate removes the opportunity to get more thrust beyond the derate level that is selected.
Depends on the installation. If the derate is not constrained by the system, there may be a problem.