(10)
ARINC Communications Addressing and Reporting System (ACARS) (Fig. 10)
(a) The FMC transmits and receives data to and from a ground based transmitter/receiver through the ACARS modular unit. The data transfer consists of predicted winds, flight plan, preflight load, and request for position. The data is transferred over a low speed digital bus.
(11)
Air Data Computer (ADC) (Fig. 11)
(a) Each FMC receives data pertaining to airplane speed and enviromental conditions from either the left, center or right ADC. The FMC's source data is dependent upon the captain's and F/O's ADC source select relays. These relays contain an interlock prohibiting the simultaneous selection of the center ADC. Each FMC receives two ADC data inputs, via the relays. The selected input, for source data, is dependent upon the status of the autopilot as well as the source select switches. The FMC source selection logic for ADC data is as follows: 1) If no autopilot or flight director is engaged, or only the
left or center channel autopilot is engaged:
The FMC will select ADC from the input port indicated by the state of the CAPT's ADC source select analog input. 2) If the autopilot is not engaged but the captain's flight director is on:
The FMC will select the ADC from the input port indicated by the state of the left ADC source select analog input.
3) If the autopilot is not engaged and only the F/O's flight director is on:
The FMC will select the ADC from the input port indicated by the state of the F/O's ADC source select analog input.
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4) If only the right channel autopilot is engaged:
The FMC will select the ADC from the input port indicated by the state of the F/O's ADC source select analog input.
5) If the autopilot is in multi-channel operation:
The ADC selection will be determined by the first autopilot engaged.
If the first autopilot disengages, the FMC shall maintain its current ADC selection.
6) If a selected ADC source is determined to have faulty data:
The next closest valid channel input shall be utilized for data unless otherwise specified.
(b) The data supplied by the ADCs is sent over a low speed digital bus and consist of the following: 1) Altitude 2) Computed airspeed 3) Impact pressure 4) Indicated AOA 5) Mach 6) Maximum operating schedule 7) Static air temperature 8) Total air temperature 9) Total pressure 10) True air speed
(12) Control Display Unit (CDU) (Fig. 12)
(a)
Both CDUs are directly connected to each FMC and may display data alternately from either FMC based on the associated NAV source select switch position.
(b)
Each CDU may operate independently and simultaneously display different data pages. However, CDU entries must be processed by both FMCs in order that flight plan changes, selected modes, and other data entered by either pilot will be consistent between the two systems.
(c)
In the dual FMC configuration the left FMC may be termed as the button push master. Button pushes originating from either CDU are first processed by the left FMC. The left FMC decides which button pushes should be executed in what sequence and controls the CDU to FMC communications link. It in turn sends button push messages and other information via the intersystem bus to the right FMC. Each FMC processes the button pushes and updates its own CDU display screen directly.
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(d) The data between the CDUs and FMCs is transmitted over a low speed digital bus.
(13)
Primary Flight Display (PFD) (Fig. 13)
(a) PFD data, from the FMC, is transmitted over a high and a low speed digital bus. The data consists of speed related data to be displayed on the speed tape, and data to be displayed on the compass rose and vertical deviation scale. The data sent over the high speed data bus is drift angle. Data sent over the low speed data bus is as follows: 1) Cross track angle 2) Desired track 3) Track angle 4) V1 speed 5) VR/VREF speeds 6) Max min maneuver speeds 7) Vertical deviation 中國航空網 www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：747-400 AMM 飛機維護手冊 導航 NAVIGATION 3(116)
