429 56 A52 DADC-L-3 IAS/MACH
XMTR 57 A43 F/S ENABLE
M196 DADC 1(E1-1) WORD
FMC LOGIC
VALID
D311A D1649
(SEE TABLESNOT THROTTLE UPFOR WORDS) IAS/MACH DAMP
429 56 A52
DADC-R-3 TAKEOFF MODE
XMTR
57 A43
M368 DADC 2(E1-1) N1 LIMIT
SELECTED N1SELECTION LIMIT
(FIG 7)
D2163B
429 C10
A54
IRU-R-3 SELECTED N1
XMTR C11 A45 LIMIT IS INVALID
ARINC 429 (FIG 7)
RECEIVERSM1162 IRS 2(E3-5)
WORD
VALID
D2161B D1647 (SEE TABLES
FOR WORDS)
429 G7 A34
IRU-L-3
XMTR
G8 A45 M1161 IRS 1(E3-5)
M917 A/T COMPUTER (E1-1)
A
737-300/400/500MAINTENANCE MANUAL
(2)
The DFCS, through DFCS discrete word 274, requests an Autothrottle mode that is compatible with the Autopilot pitch mode. The requests are MCP or FMC SPEED, N1, and cruise descent retard (Retard 2). Arm is the absence of any other request. The actual mode of operation is determined by internal mode logic, defined by tables that follow.
(3)
A number of discrete logic signals, derived from the DFCS and FMC discrete words, are used throughout the A/T system for mode logic and control. These logic signals are denoted along with their destination references.
(4)
The various N1 limits are provided by the Flight Management Computer. The appropriate limit is selected for use in the generation of the N1 command. Limit selection is based on a command from the DFCS, or, if the VNAV is engaged in the Autopilot, the limit is selected by discrete commands from the Flight Management Computer.
B. Discrete Input Words
(1)
Autothrottle operation is controlled by the Autopilot; or if not commanded by the Autopilot, it can be controlled by the FMC. The commands and mode logic are transmitted from the Flight Control Computers, through the mode control panel, via ARINC 429 discrete words 270, 272, and 274. Control logic is transmitted from the Flight Management Computer via ARINC 429 discrete word 275.
(2)
Each command received via the discrete words are requests to the Autothrottle, and internal mode logic must be satisfied to set or enable the requested mode or function.
16. A/T Operating Limits and Control________________________________
A. Min Speed, Reversion and Gain (Fig. 7)
(1)
A minimum speed command is provided to prevent the airspeed command from producing a low airspeed or an excessive angle of attack. The minimum speed value, computed within the Autothrottle, is used when the Autopilot is in any mode other than VNAV. When the Autopilot is in VNAV, a minimum speed value computed by the FMC is used.
(2)
In the Autothrottle, the alpha floor is computed as a maximum angle of attack, based on flap position during approach and mach during cruise. The maximum alpha is compared to angle of attack, damped by pitch attitude rate and converted to an equivalent minimum airspeed error, which is provided to the airspeed command circuit.
(3)
If VNAV is engaged in the autopilot, FMC minimum speed is compared to computed airspeed and the resultant error is provided to the airspeed command circuit.
(4)
Speed command gain is adjusted to minimize throttle activity, except during approach when fast response is required. There are three levels of gain control: approach, capture, and track.
(5)
Approach gain, used for the landing phase of flight, is set when in speed mode if glideslope capture, or radio altitude is less than 2000 feet and flaps are greater than 12.5 units.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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Min Speed, Reversion, and Gain
Figure 7
A
737-300/400/500MAINTENANCE MANUAL
(6)
Capture gain, used for nonapproach maneuvering, is set two seconds after transition to the following conditions. Reset is also delayed for two seconds. Capture is defined as not approach but in a maneuvering condition; flaps greater than 0.5 unit, minimum speed, not in speed mode, Autothrottle disengaged, invalid N1, or not in altitude acquire or hold.
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