Originally Posted by
WorkingHard
Not sure if this question should be here but this thread promted it. I only fly piston engined aircraft and so the take off run at anything less than full power is quite alien to me. Why, please, are turbine engined a/c not set to full power for take off (except for noise abatement)? ...
Probably the biggest difference piston vs jet is the percentage of MTOW in fuel load. If the fuel tanks are only 20% full, the plane is VERY light, and a full-rated thrust TO can be pretty wild for the passengers. If there's plenty of runway available, it doesn't make good sense to thrash the engines more than really necessary.
Two methods of reduction are widely recognized and used: Derate or Alternate rating (a fixed thrust decrease, usually based on an early model of an advanced engine), and Flex or Assumed Temp. Method (see
here for a description).
You can also search around pprune for earlier threads on this topic.