737 Flight Crew Operations Manual
Engines, APU -
Engine System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 7.20.5
The full rated takeoff thrust for the installed engine is available at a thrust lever
position less than the forward stop. Fixed or assumed temperature derated takeoff
thrust ratings are set at thrust lever positions less than full rated takeoff. The
maximum rated thrust is available at the forward stop. The EEC limits the
maximum thrust according to the airplane model as follows:
Note: Typical engine ratings based on model/series airplane. For actual engine
ratings refer to Performance Dispatch chapter.
• 737-800 – CFM56-7B27 rating
EEC Alternate Mode
The EEC can operate in either of two alternate modes, soft or hard. If required
signals are not available to operate in the normal mode, the EEC automatically
changes to the soft alternate mode. When this occurs, the ALTN switch
illuminates and the ON indication remains visible. In the soft alternate mode, the
EEC uses the last valid flight conditions to define engine parameters which allows
the mode change to occur with no immediate change in engine thrust. Thrust
rating shortfalls or exceedances may occur as flight conditions change. The soft
alternate mode remains until the hard alternate mode is entered by either retarding
the thrust lever to idle or manually selecting ALTN with the EEC switch on the aft
overhead panel.
Note: Loss of either DEU results in a loss of signal to both EECs. The EEC
ALTN lights illuminate and each EEC reverts to the alternate mode to
prevent the engines from operating on a single source of data.
When the hard alternate mode is entered, the EEC reverts to the alternate mode
thrust schedule. Hard alternate mode thrust is always equal to or greater than
normal mode thrust for the same lever position. If the hard alternate mode is
entered by reducing the thrust lever to idle while in the soft alternate mode, the
ALTN switch remains illuminated and the ON indication remains visible. When
ALTN is selected manually, the ON indication is blanked.
Structural Limit Protection
The EEC provides N1 and N2 redline overspeed protection in both normal and
alternate modes. The EGT limit must be observed by the crew because the EEC
does not provide EGT redline exceedance protection.
September 26, 2013
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