(2)
The FCC is divided up into various sections in order to handle the various inputs and outputs. One of these sections handles the cruise and approach modes of operation.
(a)
The cruise modes are: 1) Control Wheel Steering, Heading Hold, and Attitude Hold 2) Heading Select 3) VOR Mode 4) L NAV mode
(b)
The approach modes are:
1) Take-off
2) LOC Approach mode
3) Go Around mode
(3)
All processing is accomplished with digital computation. Inputs from the inertial reference system, flight management computer, air data computer and the mode control panel are connected in ARINC 429 receivers. Roll attitude and roll acceleration are normally from the on side. Inputs from the roll force transducer, VHF navigation receiver and low range radio altimeter (LRRA) are connected to analog to digital (A/D) converter. The feedback signals, aileron position sensor and aileron actuator position transducer (LVDT) are used in the output section directly. These signals are also connected to an A/D converter to provide additional signal for monitoring purposes.
(4)
Engage logic is processed both in the MCP and the FCC. Hydraulic solenoids in the A/P actuator are energized to activate A/P control. Mode selection is determined as a function of both the FCC and the MCP.
(5)
The FCC provides outputs to the flight mode annunciator (FMA) to visually inform the pilot of the mode or status of the system. The master FCC is in control of mode selection. Each mode is processed by the A/P roll command computer. The A/P roll command computer determines the roll command and roll rate. The maximum bank limit is set at 30°. This limit may be reduced by the selector switch on the MCP in 5° increments to 10°, except CWS, L NAV and LOC capture. The limit is automatically reduced to 8° in VOR/LOC on course. In heading select, VOR capture, L NAV and LOC OC, the roll rate is limited to 4° per second. After VOR OC the roll rate is limited to 1.3° per second. In the LOC capture mode, the roll rate is increased to 5.5° per second. The roll command is converted to an analog signal. The signal is then amplified and applied to the aileron actuator. Aileron actuator positioning (LVDT) is returned as a feedback signal. The aileron position sensor is used prior to engaging the A/P to synchronize the FCC, A/P actuator with the surface position.
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A 737-300/400/500MAINTENANCE MANUAL
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A
737-300/400/500MAINTENANCE MANUAL
(6)
Surface position monitor (SPM) is a dual channel monitor which monitors aileron position against LVDT position to detect for relative motion. Autopilot actuator monitor (AAM) monitors A/P command against LVDT for relative difference.
(7)
The actuator in turn mechanically provides an input to the Power Control Unit which hydraulically and mechanically operates the ailerons. This output is also fed through the spoiler mixer which causes the spoilers to move and assists the ailerons in the lateral control of the airplane. The "B" FCC has a separate aileron actuator and PCU to provide the same inputs.
(8)
The F/D signal processing is very similar to the A/P signal processing. A command mode logic is used, however, the F/D command processing is accomplished as a separate control. The digital output is converted to an analog signal prior to being applied to the ADI. Each FCC provides an output to its respective ADI. However, in TO/GA, or in an approach below 800', a bus transfer takes place and the F/D command is relayed from the other FCC. This information is transmitted over the cross-channel bus, received by the local FCC and then converted to analog to be used as the F/D command.
K. Roll Channel Analog Interface (Fig. 25)
(1)
The analog interface diagram illustrates the various LRU's which are associated with the generation and implementation of signals used during roll channel modes of operation. All of the input signals are converted from analog form to digital for internal use by the computer. In addition, all of the output signals are converted from digital to analog prior to going to their respective destinations.
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