Originally Posted by
VinRouge
Fuel critical sector, max rated TO provides lowest burn.
however, cost in terms of engine life are significant so most stick with derate/flex for commercial reasons. unless you have an engine maintainance contract that doesnt mention flex/drt vs Max, in which case, let er rip!!!
Several years ago, we were investigating a particular Asian airline that had horrible time-on-wing for their 737/CFM56 engines. Mainly sort haul, they were running out of EGT margin in ~3,000 hours - at a time when the typical operator was in the range of 15,000-20,000 hour time on wing.
Come to find out, they were using max TO every single takeoff - never a derate of any kind. At around a million dollars to overhaul an engine, you'd have to save a whole lot of of fuel to justify an extra two million dollars/year in engine maintenance...