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EFFECTIVITY
GUN ALL 73-21-00
Page 53
D633A101-GUN Feb 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
73-21-00-017
Electronic Engine Control
The electronic engine control (EEC) is a two-channel computer.
The two channels (A and B) are independent but connect by a
cross channel data link (CCDL) during engine operation. The
EEC chooses either channel A or B as the active control
channel. The active channel changes at each engine start if N2
speed during the previous engine run was more than 76 percent
and both channels are valid. If the active channel is not valid,
the EEC changes the standby channel to the active channel.
The EEC goes to single channel operation when the CCDL is
inoperative or when one EEC channel is not powered from the
EEC alternator. While in single channel operation, the active
channel does not use sensor data from the standby channel.
Electrical Power Supply
The normal power supply for the EEC is the EEC alternator. The
EEC can also use ac electrical power from the related airplane
transfer buses. See the EEC ELECTRICAL POWER SUPPLY
pages in this section for more information on EEC power.
Ignition System Control Power Supply
The transfer buses supply ac power for ignition. The EEC
operates the left ignition system with transfer bus power.
The ac standby bus also supplies electrical power for ignition.
The EEC operates the right ignition system with ac standby bus
power. See the ignition section for more information.
(CHAPTER 74)
Thrust Lever Control Inputs
Thrust lever movement changes the position of the thrust lever
resolver (TLR). The TLR sends a thrust lever resolver angle
(TRA) signal to the EEC. The EEC uses the TRA signal to control
engine operation for forward and reverse thrust. See the
ENGINE THRUST MANAGEMENT PAGE in this section for more
information thrust management. See the engine controls
section for more information. (CHAPTER 76)
Engine Temperature Sensors
The EEC uses engine air temperature to control the servo fuel
system. The EEC uses the fuel servo system to make sure the
engine provides the required thrust. These are the engine
temperatures used to control the fuel servo system:
* TAT (Total air temperature)
* T25 (High pressure compressor inlet temperature)
* T3 (High pressure compressor discharge temperature)
* HPT case (High pressure turbine case temperature).
The EEC also gets T49.5 temperatures from engine sensors.
These temperatures are used for engine protection during
starting.
ENGINE FUEL AND CONTROL - ENGINE CONTROL - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN ALL 73-21-00
Page 54
D633A101-GUN Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
CFM56 ENGINES (CFM56-7) 737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
73-21-00-018
The EEC gets TAT from the T12 sensor on the engine and from
the two ADIRUs. The T12 sensor has two elements, one for
channel A and one for channel B. The TAT probe for the ADIRUs
is heated to prevent ice on the probe. While on the ground, if at
least one T12 value is valid, the EEC uses only the engine T12
probes for TAT to prevent errors when there is not enough air
flow over the heated ADIRU TAT probes. The EEC uses the
ADIRU TAT signals 5 minutes after the airplane goes in-flight.
The EEC assumes the airplane does not have aspirated TAT
probes. On an airplane with aspirated probes, the EEC still uses
the T12 sensor to get TAT while on the ground and until 5
minutes after the airplane goes in-flight.
While in-flight, if all four total inlet temperature signals are valid
and in limits, the engine uses the total air temperature from
ADIRU 1 for control. The EEC uses an ADIRU temperature
before it uses the engine T12 sensor temperature so that both
engines use the same value for TAT when possible. If both
ADIRU temperatures are not valid, the EEC uses the T12 values
for TAT.
The EEC uses TAT for power management, VBV, HPTACC, and
LPTACC systems control.
The EEC gets T25 temperatures from the PT25 sensor. The PT25
sensor has two temperature elements, one for channel A and
one for channel B. If both T25 values are valid and are in limits,
the EEC uses the average of the two temperatures. If one T25
value is not valid, the EEC uses the other T25 value. If both
values are not valid, the EEC estimates T25 with other engine
parameters.
The EEC uses T25 to control the VSV, TBV, and VBV systems.
The EEC gets T3 temperatures from the T3 sensor. The T3
　
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