This bulletin provides information advising flight crews of thrust shortfall that may occur when the assumed temperature method of reduced takeoff thrust is used in combination with takeoff derates on 767-200 airplanes.
On 767-200 airplanes with takeoff thrust derate capability, after selecting Takeoff Derate 1 or 2, additional takeoff thrust reductions can be obtained using the assumed temperature method. The Thrust Management Computer (TMC) calculates derated takeoff thrust %N1 (derate 1 or 2) including any assumed temperature selected on the Thrust Mode Select Panel (TMSP).
It was determined that the originally published %N1 data for assumed temperature reduced thrust with Takeoff Derate 1 or 2 are incorrect. These data are also incorporated into the -304 TMC. The incorrect data may result in a thrust shortfall if assumed temperature reduced thrust is used in combination with Takeoff Derate 1 or 2. Assumed temperature reduction applied to full rated takeoff thrust does not result in such an adverse affect. The Takeoff Derate 1 and 2 assumed temperature reduced thrust setting data have been revised. The revised data has been incorporated in the -305 TMC. Boeing Service Bulletin 767-22-0022 is available for converting a -304 TMC to a -305 TMC.
Until Boeing Service Bulletin 767-22-0022 is incorporated, do not use assumed temperature reduced thrust with Takeoff Derate 1 or 2 selected.
Assumed temperature reduced thrust may be used with Full rated takeoff thrust.
This Operations Manual Bulletin will be canceled after Boeing is notified that all affected airplanes in the operators fleet have been modified by Boeing Service Bulletin 767-22-0022.