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737-300/400/500MAINTENANCE MANUAL
I. GO-AROUND - the DFCS controls airspeed, and the A/T maintains either reduced or full GA N1. Reduced go-around is engaged by pressing the TO/GA switch one time. A second press of the TO/GA switch engages maximum go-around. Other modes can be selected after engines have achieved the selected N1 limit and radio altitude is greater than 100 feet.
13. Signal Interface (Fig. 4)________________
A. Figure 4 shows the general signal flow and processing within the A/T system. Detailed interface and signal processing is provided by schematic diagrams that follow.
B. The A/T computer is provided with mode, control, and sensor signals, shown on the left. It computes the necessary throttle position and provides drive to the servo assembly to position the engine power levers.
(1)
AIRPLANES WITHOUT EFIS; The A/T provides mode annunciation and A/T disengage warning through the FMA; and fast/slow commands displayed on the ADI's.
(2)
AIRPLANES WITH EFIS; The A/T provides mode annunciation on the EADI's via the EFIS symbol generators, and A/T disengage warning on the Autoflight Status Annunciators. A/T status and data is provided to the Flight Control computers and the Flight Management Computer.
C. Power
(1) The A/T system requires both 115 volt ac and 28 volt dc power. An internal power supply provides the dc operating voltage for the computer and ac voltage used for demodulation reference and excitation to the power lever angle synchros.
D. Input Interfaces
(1)
The A/T computer receives both digital and analog signal inputs. The digital inputs are received by way of ARINC 429 digital data buses, from other digital systems, such as: Autopilot, Flight Management Computer, Air Data Computers, and the Inertial Reference Units.
(2)
The analog and discrete inputs, received from various sensors and interfacing systems, are converted to digital format within the A/T computer.
E. Digital Interfaces
(1)
The Autopilot, through its mode control panel, the Flight Management Computer, both Air Data Computers, and both Inertial Reference Systems, provide their commands, data, and discrete logic by way of six ARINC 429 digital data buses. The bus signals are received, the desired data words selected, and the data converted into a format acceptable to the computer's digital processor.
(2)
The Autopilot provides the airspeed target, MCP selected altitude, flight path angle rate, and discrete mode select logic. Through the discrete logic, the Autopilot requests a specific A/T operating mode, and with the N1 mode set, selects the appropriate N1 limit.
(3)
The Flight Management Computer provides N1 limits and target, FMC minimum speed, SAT, FMC selected altitude, airplane gross weight, and discrete mode logic. Through the discrete data words, the FMC provides the A/T with the executed FMC mode, and when the Autopilot is engaged in VNAV mode, the FMC provides N1 limit selection.
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A 737-300/400/500MAINTENANCE MANUAL
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737-300/400/500MAINTENANCE MANUAL
(4)
The Air Data Computers provide CAS used for the airspeed mode feedback, altitude, altitude rate, and total air temperature. If valid, the data from ADC-1 is used by the Autothrottle. If ADC-1 is not valid, then the A/T selects ADC-2 output. If both sources for a specific data is invalid, and the signal is required for the engaged mode, disengage logic is generated.
(5)
The Inertial Reference Units provide airplane altitude, airplane axis and flight path accelerations, and ground speed. Again, system 1 data is normally used by the A/T if the data is valid, or if system 1 data is invalid, system 2 is selected as the data source.
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