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approximately 800° to 805° C and attempts to maintain the TGT below
820° C (maximum overtemperature).
If the temperature control switch in the crew compartment is set to ON, an
increase in TGT more than the pre-set limit causes the amplifier to
energize the motor in the actuator. The motor turns the output shaft which
operates the throttle control mechanism to decrease the quantity of fuel
from the HP fuel pump. This decreases the TGT.
When the engine goes to the over-temperature condition (more than the
amplifier datum temperature), the TTC actuator is moved in the appropriate
direction to decrease the fuel supply.
NOTE:
Should manual control of the engine become
necessary, an external ON-OFF switch can be
selected to OFF. In this condition, the TTC actuator is
moved to the no-trim stop. In this position, a full range
of control at the throttle levers is available.
3. Flight Manual Limitations:
There are no Flight Manual limitations established for the electronic engine control
system at the time of this revision.
2A-76-30: Engine Thrust Management System
1. General Description:
The engine thrust management system provides a means of setting and
controlling idle thrust, forward thrust and reverse thrust.
Engine thrust is indicated as a measurement of the ratio of fan pressure to intake
total pressure. It is referred to as Engine Pressure Ratio (EPR). The air data
computer supplies intake pressure information from four probes in the bypass
duct. These signals are sent to a transducer, adjusted to a common EPR/thrust
value for the engines and displayed on the EICAS (annunciator page). The
engines are set to a predetermined EPR for takeoff, climb and cruise.
A. Subsystems, Units and Components:
The engine thrust management system is composed of the following
subsystems, units and components:
• Power Levers
• Thrust Reverser Levers
• Airflow Control System
OPERATING MANUAL
2A-76-00 PRODUCTION AIRCRAFT SYSTEMS
Page 2
May 31/01
Revision 4
• Autothrottle
• Engine Synchronizer
2. Description of Subsystems, Units and Components:
A. Power Levers:
The power lever assembly consists of left and right power levers for setting
forward thrust. The power levers are mechanically connected to the input
lever on the fuel flow regulator to permit manual selection of fuel flow and
engine RPM.
B. Thrust Reverser Levers:
The thrust reverser lever assembly for each engine is mounted in the
cockpit control pedestal. It consists of a power lever (forward thrust lever)
and a smaller lever called the reverse thrust lever, mounted and pivoting on
the upper portion of the throttle lever. Both levers operate a bellcrank
common to both levers through an interconnecting link assembly. The
bellcrank, in turn, is connected to a cable sector wheel (at the cockpit floor
line) by a push-pull rod. This makes it possible to utilize the same cable
run, push-pull rods, and bellcranks when selecting engine speed. To
prevent one lever from being moved when not desired, an interlocking
mechanism is provided. This consists of a roller attached to the
interconnecting link assembly riding in a contoured slot. The design permits
moving the power lever from its IDLE position toward the maximum forward
thrust position without moving the reverse lever. The roller in the slot is
locked from following the contour of the power lever track. Only when the
power lever is moved back to its IDLE position, can the reverse lever be
moved in its upward/aft direction. This, in turn, moves the bellcrank in the
same direction, thereby preventing it from being moved due to the roller
being in the slot. Moving the reverse thrust lever from its stow (IDLE)
position towards its maximum reverse thrust position will allow for an
increase in HP compressor speed.
C. Airflow Control System:
The airflow control system is designed to prevent compressor stalls or
surges during stable and transitioning compressor speeds. The system
includes variable Inlet Guide Vanes (IGVs) located forward of the first stage
of the HP compressor and a bleed strap surrounding the 7th stage of the
HP compressor.
The varying positions of the IGVs ensure correct airflow to the first stage of
the compressor. The bleed strap prevents “choking” of the HP compressor
rear stage. This is accomplished by opening and dumping compressor air
into the bypass and increasing airflow through the HP compressor front
stages at the same time, thus preventing stalls.
The variable guide vanes and bleed valve are controlled by an airflow
regulator and actuator. This unit responds to changes in EPR which is a
　
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