787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Engines, APU -
Engine System Description
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 7.20.7
Thrust protection is not provided in the alternate mode and maximum rated thrust
is reached at a thrust lever position less than full forward. As a result, thrust
overboost can occur at full forward thrust lever positions. The EICAS caution
message ENG LIMIT PROT (L, R) is displayed if the thrust lever position
commands an N1 greater than the maximum rated thrust (maximum N1). N1 and
N2 red line protection is still available in the alternate control mode.
Overspeed Protection
[Option – GE engines]
The EEC monitors N2 rotor speed and commands reduced fuel flow if the rotor
speed approaches its redline limit. The EICAS advisory message ENG RPM
LIMITED (L or R) is displayed when RPM limiting is in effect. If the redline limit
is exceeded, the EICAS caution message ENG LIMIT EXCEED (L or R) is
displayed.
[Option – RR engines]
The EEC monitors N1, N2, and N3 rotor speeds and commands reduced fuel flow
if any rotor speed approaches its redline limit. The EICAS advisory message ENG
RPM LIMITED (L or R) is displayed when RPM limiting is in effect. If the redline
limit is exceeded, the EICAS caution message ENG LIMIT EXCEED (L or R) is
displayed.
[Option – GE engines]
Overspeed protection is provided on the N2 shaft (N1 is indirectly protected by
the N2 protection). If RPM limiting fails and an overspeed condition persists, the
EEC commands fuel shut off to shutdown the engine. The EICAS caution
message ENG FAIL (L or R) is displayed with an aural beeper once the engine
falls below idle speed.
[Option – RR engines]
Overspeed protection is provided on N1 and N2 shafts (N3 is indirectly protected
by the N1 and N2 protection). If RPM limiting fails and an overspeed condition
persists, the EEC commands fuel shut off to shutdown the engine. The EICAS
caution message ENG FAIL (L or R) is displayed with an aural beeper once the
engine falls below idle speed.
If the EECs are in alternate mode, advancing the thrust levers full forward
provides some overboost and should be considered only during emergency
situations when all other available actions have been taken and terrain contact is
imminent.
Thrust Ramping
[Option – GE engines]
During takeoff, the EEC compensates for high stress loads on engine fan blades
due to crosswinds and low groundspeed by slowly increasing thrust until takeoff
thrust is achieved, a process known as thrust ramping.
February 15, 2010
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