Many operators use reduced thrust takeoff whenever performance limits and noise abatement procedures permit. Thrust reduction or derate lowers EGT and extends engine life.
The first method is Assumed Temperature Method (ATM), this method achieves a takeoff thrust less than the full rated takeoff thrust by using an assumed temperature that is higher than the actual temperature. The maximum thrust reduction authorized by most regulatory agencies is 25% below any certified rating, on the 767 PW4000 could be as low as 1.39 EPR and on 737NG as low as 89% N1. (GE
use N1 as reference and PW
The second method is fixed derate which uses a takeoff thrust less than full rated thrust for which complete and independent performance data are provided in the Airplane Flight Manual. Derated thrust is obtained by selection of fixed tkeoff derates from the Flight Management Computer (FMC). TO1/CLB1 provides a takeoff/climb limit reduced 3%N1 (approximately 10% thrust). TO2/CLB2 provides a takeoff/climb reduced by 6%N1 (approximately 20% thrust).
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