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A DEEC is provided for each engine. The DEEC is basically an N1 governor
with provisions for fuel limits during acceleration and deceleration.
The DEEC performs governing, limiting, and fuel scheduling
functions for engine start and continuous operation.
Input parameters utilized by the DEEC for controlling functions are:
engine inlet pressure (PT2), engine inlet temperature (TT2), interstage
turbine temperature (ITT), low-pressure rotor speed (N1), high-pressure
rotor speed (N2), and Thrust Lever Angle (TLA).
Output signals from the DEEC to control engine operation go to the hydromechanical
fuel control unit, surge bleed valves and ignitors.
The crew is able to control the engine through the DEEC by changing
the TLA input to change desired thrust level. Primary TLA is received
from the RVDT. Secondary TLA is sensed by the DEEC from a potentiometer
within the hydromechanical fuel control unit during manual
mode operation.
TT2 and PT2 input is provided by a temperature/pressure sensor integrated
into the inlet duct. The sensor contains an electrical element for
sensing temperature (TT2). Inlet pressure (PT2) is applied directly to the
DEEC through a flexible line. An electrical heating element on the sensor
provides protection against icing. The PT2 line from the sensor shall
be treated as an aircraft pitot line with a drain trap located at the low
point for draining possible moisture accumulation. In the normal operating
mode, the DEEC analyzes the TT2 and PT2 inputs and produces
output signals which are sent to a torque motor in the hydromechanical
fuel control unit for fuel flow control and to the control solenoids of the
surge bleed valves.
ITT is measured by thermocouple probes that extend into the gas path
between the high-pressure (N2) and low-pressure (N1) turbines.
The N1 speed signals are produced by a dual element monopole located
in the rear bearing housing and are the primary thrust indicating instruments.
The N2 speed signal is produced by a dual element monopole
located in the transfer gearbox. Both dual element monopoles
provide outputs to the DEEC and EICAS for flight deck display. Output
signals from the DEEC for engine control are also directed to a torque
motor in the hydromechanical fuel control unit and to the control solenoids
of the surge bleed valves.
Pilot’s Manual
2-6 PM-126A
The DEEC has an extensive self-monitoring and fault analysis system.
In the event a minor fault is detected in the system, the DEEC will initiate
an ENGCMPTR FAULT white CAS when ENG CMPTR switch is
in the ON position. If electrical power to the computer is lost, the manual
mode solenoid valve is deenergized closed, engine control reverts
to manual mode, and an ENGCMPTR FAULT amber CAS illuminates.
If a major fault occurs in the DEEC, it may remain in the auto mode or
it may revert to manual mode depending on the fault. In either case,
the ENGCMPTR FAULT amber CAS will illuminate. A MAN amber EI
will also illuminate if DEEC has reverted to manual mode.
When engine control automatically reverts to manual mode, it will not
go back to normal mode until the pilot cycles the ENG CMPTR switch.
If the CAS doesn’t clear, the fault condition still exists. At this point, the
pilot may select the MAN position which will result in the ENGCMPTR
FAULT amber CAS changing to white.
Whenever engine control is in the manual mode of operation, a MAN
amber or white EI will illuminate. If engine control has reverted to
manual because of a DEEC fault or failure, MAN will illuminate amber.
If manual mode was selected by the pilot, MAN will illuminate white.
Engine operation during manual mode is maintained through the secondary
TLA and mechanical linkage to the hydromechanical fuel control
unit.
Power to the DEEC is 28-vdc supplied from the L and R ESS buses
through the 7.5-amp L and R CMPTR circuit breakers located within
the ENGINE groups of the respective pilot’s and copilot’s circuit breaker
panels.
The following CAS illuminations are specific to the DEEC:
The DEEC also functions to provide the crew with automatic performance
reserve and engine synchronization.
CAS Color Description
ENGCMPTR FAULT Amber There is a major fault in the associated (L or
R) engine computer system.
ENGCMPTR FAULT White There is a minor fault in the associated (L or
R) engine computer system.
Pilot’s Manual
PM-126A 2-7
AUTOMATIC PERFORMANCE RESERVE (APR)
Automatic Performance Reserve (APR) provides a change in thrust on
the operating engine in the event of opposite engine thrust loss during
takeoff and missed approach conditions. The APR is controlled by the
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