USMC:
The reduced-thrust concept was new to me, too, upon training for my first airline job. I was told:
The last 10% of an engine's rated-thrust is where 90% of the engine failures occur.
As a guy with an engineering background, I can buy that, from a fatigue, manufacturing tolerance, or materials variance perspective.
Thrust is not linear with RPM; it is exponential. 90% rpm is roughly 50-60% of total thrust available at 100% rpm. Small reductions in rpm are big reductions in thrust, and the probability of engine failure is directly proportional to the amount of thrust coming out of the tailpipe. One instructor told me a 2% rpm reduction lowers the probability of failure by 50%.
The numbers must bear it out...I don't think the FAA would approve it otherwise.
Given the same background as you, I was surprised to find that
heavy-weight takeoffs in the 747 (sim) were
easier at
reduced thrust than lightweight, with any power setting.
Why?
The sim instructor almost always fails an outboard engine, giving you the maximum assymetric moment-arm. Higher weights mean faster rotation and V1/V2 speeds.
And the faster you are going, the more effective the vertical fin and rudder. Reduced thrust lowers the assymetry.
