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MAINTENANCE MANUAL
(b)
Actual engine thrust is indicated by both actual thrust pointers and digital readout. Any momentary difference between actual thrust and commanded thrust is shown by the command sector. The maximum thrust limit as computed by the TMC or EEC is shown by an amber marker on the analog scale.
(c)
Target thrust (reference EPR) is shown by a reference cursor on the analog scale and a digital readout above the actual thrust readout. The thrust limit mode and assumed temperature (if selected) are shown above the EPR indicators. When an assumed temperature is selected while the airplane is on the ground, a D appears in front of the thrust limit mode (only valid when in Take-Off EPR reference mode).
(d)
Digital displays are also provided for total air temperature (TAT) and thrust reverser status. If a thrust reverse lever is fully deployed, the readout (REV) is green. The readout is yellow while the lever is in transit. For normal in-flight conditions, the readout is blank.
(e)
The manual THRUST REF SET control on the EICAS control panel consists of a dual rotary switch combined with a push-pull switch. The inner control is a continuously rotating control with 12 detents per revolution. When initially set (pulled out), the readout corresponding to the engine selector switch (L, R, or BOTH) defaults to 1.55 EPR. Clockwise rotation of the control increases the readout and counter clockwise rotation decreases the readout. The rotation sensitivity is
0.01 EPR per detent. When a readout is modified manually its last input data is retained, regardless of engine selector switch position, until the inner control is set (pushed in). The outer control is a three-position rotary switch that selects the L (left), BOTH, or R (right) EPR readout.
(5) Thrust Management System - Engage/Disengage Logic (Fig. 9)
(a) The engage-disengage logic consists of both engage and mode logic. Major input signal sources supplying information for engage/disengage control laws are the FMC, MCP, EECs, and ADCs. All inputs are used to control the motor excitation relay, which connects excitation power and control inputs to the A/T servomotor generator.
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(b)
Input signals converted by software include digital and analog discretes, and digital variable signals. Analog discrete signals used for logic functions are sent to A/D converters before software usage.
(c)
Analog discrete inputs:
1) A/T disconnect and reverse thrust
2) Air/ground
3) Autothrottle arm
(d)
Digital variable inputs (from ADCs):
1) Calibrated airspeed
2) Filtered standard barometric altitude
(e)
Digital discrete inputs: 1) VNAV mode operational, throttle retard, and thrust mode
request (from MCP) 2) EEC off and EEC valid (from EECs) 3) A/T dormant, thrust request, and idle request (from FMCs)
(f)
When the A/T switch is in the ARM position, the TMC is enabled to engage the autothrottle servo. The servo controls thrust according to manually or automatically selected operating modes, provided there are no detected faults in the system. Any detected fault affecting autothrottle operation in the selected mode results in servo disengagement and corresponding annunciation on the EICAS display unit. Manual engagement into SPD or EPR (or THR) modes is obtained by pressing the corresponding switch on the MCP. Automatic engagement occurs when either the FLCH or VNAV mode is selected and is successfully engaged in the AFDS. When the autothrottle is engaged, the operating mode is displayed on the lower left corner of the EADI. Disengagement of the autothrottle occurs if: 1) A fault affecting autothrottle operation in the selected
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