(b)
Digital data bus inputs: 1) Autothrottle inputs from the MCP (discrete) 2) Control inputs from the FMCs: thrust mode valid, thrust
mode REQ, A/S mode REQ, and Mach mode REQ are discrete signals; and Mach selected and airspeed selected are variable signals.
3) Environmental data from the ADCs (variable)
(c)
Analog inputs:
1) Flap position from the flap/slat electronic unit
(d)
Analog discrete inputs: 1) Autothrottle arm from the MCP, and ground test from the MCDP.
2) Go-around engage from the go-around switches and in air from the air/ground relay.
(e)
Logic Modes
1) The autothrottle has three basic modes of operation: speed, thrust, and vertical speed. The speed (SPD) mode allows the autothrottle to control to either airspeed or Mach, depending on the control parameter selection. The thrust control mode provides control to a target EPR command, EPR reference limit, or MAX or MIN EPR limit depending on the flight condition. The Flight Level Change (FLCH) mode provides automatic control of thrust to EPR REF for climb and to the computed aft limit for descent. The Vertical Navigation (VNAV) mode transfers control of pitch and thrust to the FMCS. When the autothrottle is engaged, the operating mode is annunciated on the lower left corner of the EADI.
(f)
The following output signals to the EADI (for annunciation) are digital discretes: 1) EPR, IAS, and MACH mode 2) THR-HOLD, IDLE, and TEST mode 3) FLAP LIM, ALPHA, IAS LIM, and MACH LIM mode 4) FLCH and GA mode
(8) Thrust Management System - Thrust Limit Mode Logic (Fig. 11)
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PRIMARY THRUSTPARAMETER
TMC Thrust Limit Schematic
Figure 11
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757
MAINTENANCE MANUAL
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A
(a)
(b)
(c)
(d)
(e)
(f)
(g)
757
MAINTENANCE MANUAL
The thrust limit mode logic sets the mode for thrust limit
calculations. Thrust modes are selected by TMSP switch
engagement, FMC request when the VNAV mode is engaged, or upon
power-up based on the flight condition.
Selection of a thrust limit mode disengages the mode that is in
operation unless the conditions that follow occur:
1) Reverse thrust or the landing flap is selected, or
2) the glide slope is active from an Autopilot or a Flight Director, and
3) the T/O thrust limit mode is not selected.
The thrust limit mode that is engaged continuously shows on the
upper EICAS display unit.
When VNAV is engaged with the Autothrottle on, the TMSP
switches are locked out.
T/O Mode
1) The T/O thrust limit mode are entered four ways as follows: a) A TO/GA request from the TMSP when the airplane is on ground. This can only be used if the reverse thrust modes are not engaged. b) Automatically when the flap position is less than 23 degrees and the Mach is less than 0.12. This logic sets the T/O thrust limit mode after a landing without a use of the reverse thrust. c) Automatically upon power-up on ground unless reverse thrust is engaged. d) Automatically when reverse thrust is switched from on to off while the airplane is on the ground.
G/A Mode
1) The G/A thrust limit mode is entered six ways as follows: a) A manual TO/GA request from the TMSP while in air and the VNAV mode is disengaged. b) An FMC G/A request when VNAV is engaged. c) Automatically at the TMC power up initialization in air. d) Automatically when the airplane is in the air, and the flap position is greater than 23 or the glide slope is captured. And also when the T/O thrust limit mode is not selected. e) Automatically when flaps transition from 0 to 1. f) Automatically when the Autothrottle G/A mode is engaged.
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