ORIGINAL: HalH
Airlines have been using reduced thrust takeoffs for a long time. It is rather complicated to explain but it basically is assuming a temperature that is higher than actual and using the minimum thrust required to takeoff on that runway at the actual weight of the aircraft at the assumed temp. Clear as mud ???
To oversimplify the situation, using full rated thrust on takeoff assures that the airplane will be able to lose an engine and climb away from the airport with the airplane at its maximum certificated takeoff weight at normally anticipated temperatures and altitudes on a "normal" length runway. However, high power settings result in high temperatures that reduce turbine engine life, so the reasoning for using reduced thrust is "Why use all the thrust the engine can produce if you only need 80% of it to ensure a safe single engine climb away from the airport?"
If the airplane departs an airport at less than its maximum weight, or on a cold day, or on a loonnnng runway, less thrust is required to assure the same engine-out safety margins. To figure out how much thrust reduction is allowable while still ensuring single engine climb performance, the performance gurus program their computers with all the relevant data, and a thrust reduction is calculated and presented in a document usable by flight crews.
The generic name for this document is the Runway Analysis Manual, and it consists of hundreds of pages of data for each runway at each airport the airline will be using considering all possible air temperatures and aircraft weights.
Cheers!
Jim