Mutt--
I worked for the same carrier for a long time (all on the L1011) and when these aircraft were new, maximum engine derate, to 54C, was used when able. I left some years ago and wonder if this same derate was used as the airplanes had been bashed around a lot. The maximum derate works very well when the engines are new, how about when they (and the airframe) are old and tired?