(b)
The central air data system is wired directly (no switching) to the air data instruments on the flight deck (Fig. 3) and the inertial navigation system (Fig. 4). The interface between the central air data system and both the autopilot/ flight director and air traffic control system includes a control panel which makes different operational modes possible. on airplanes LH ALL; SN ALL; AF 105-199; AZ 209-299; IB 402 and 405, plus airplanes incorporating SB 34-2016, the central air data computer interfaces with the altitude alert system (Fig. 2).
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On XA airplanes incorporating SB 34-2069 or SB 34-2076,
the central air data computer also interfaces with the ground
proximity warning system.
On AF 151,
the central air data computer interfaces with the TAT/N1 limit
system and the auto throttle system.
On LH 011-030, 051-070, 082-099; AF 121, 122, 152-199; AT ALL;
IB 406-499; GN ALL; MD ALL; VM ALL,
the central air data computer also interfaces with altitude
alert, auto throttle, flight recorder, ground proximity
warning and TAT/N1 or TAT/EPR systems (airplanes without PMS).
(c)
Each central air data computer provides a digital encoded output of pressure altitude for use by the air traffic control system (Fig. 5). Digital encoder outputs are enabled by grounding the encoder common circuit. Each computer has 12 wires of digital output (all except encoder common) connected directly to both air traffic control transponders in parallel. The encoder common from each computer is routed to the ATC control panel. On the ATC control panel (34-53-00) an altitude reporting source select switch (ALT RPTG) permits selection of either or neither central air data computer output by connecting or disconnecting encoder common and ground. A solid-state switch inside each computer automatically opens the encoder common circuit if a failure in the pressure altitude module is detected by the failure monitoring system.
(d)
The interface with the autopilot/flight director is the most complex of the different system connections made with the central air data computer system. 1) When the autopilot/flight director is operating in the INS
or HDG mode, central air data computer outputs of computed airspeed and true airspeed are required by the pitch computers and roll computers respectively (Fig. 6).
2) On LH 011-030, 051-070, 082-099; AF 115-150, 172-199; AT ALL; IB 406-499; GN ALL; MD ALL; VM ALL, true airspeed analog signals are also provided from air data computer No. 1 to the gust response suppression system. The sensor output signal from the gust response suppression system must be compensated for acceleration, roll attitude and yaw rate due to airplane maneuvering. The signals are gain programmed as a function of true airspeed since less control is needed at high airspeeds. The TAS input is biased to establish a level equivalent to 150 knots so that input signals are gradually decreased as a function of TAS above 150 knots. Autoflight is discussed in more detail in Chapter 22.
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3)
4)
5)
6)
Central air data computer outputs of pressure altitude and pressure altitude rate provide the autopilot/flight director pitch computers with the error signals that enable the autopilot to respond to altitude select commands as set on the autopilot mode select panel. Autopilot operation is discussed in Chapter 22. Fig. 6 shows the signal flow that results in the required error signals at the pitch computers. The switching in the mode select panel is shown in the normal mode of operation, selecting input signals from central air data computer 1. Relay operation is controlled by the autopilot engage switches on the mode select panel and, normally, operation is with autopilot A engaged. When autopilot engage switch B is used, the relay selects the input signals from central air data computer 2. On LH 011-030, 051-070, 082-099; AF 121, 122, 152-199; AT ALL: IB 406-499; GN ALL; MD ALL; VM ALL, the pressure altitude and pressure altitude rate outputs from the CADC allow the autopilot to also respond to vertical speed select commands as set on the autopilot mode select panel.The central air data system supports the autopilot/flight director altitude select mode by supplying two standard three-wire synchro transmitter outputs representing pressure altitude (one coarse (AC-3) and one fine (AF-3) resolution) from each central air data computer to the mode select panel of the autopilot/flight director.To use air data computer outputs in the altitude select mode, the mode select panel has either A or B autopilot engage or flight director ON switches on, the altitude mode switch in the ALT SEL position and the desired altitude dialed in on the altitude select control. Once the air data computer that will provide the altitude signals has been selected, the two inputs are routed to two difference transformers (controlled by the altitude select control) where pressure altitude is compared with desired altitude and difference or error signals are generated.The two altitude error signals are corrected for barometric pressure by control transformers (controlled by the BARO set knob) in the captain's altimeter and then routed to all three pitch computers in parallel. Thus, for autopilot altitude select mode, either central air data computer can provide two barometrically corrected altitude error signals (one coarse and one fine resolution) to all three pitch computers.
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本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航1(59)
