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(23) Autoland Mode Logic (Fig. 10)
(a)
Upon receipt of the APP mode ARMED or OPERATIVE discrete, the APP switch dot-bar matrix is illuminated. Each CMD ENGAGE switch initiates a CMDENG request discrete which goes to the corresponding FCC. A valid request generates a REQUEST ACCEPTED discrete which locks the CMD switch in the up position. The APP switch generates a similar request when pressed. Each F/D switch generates an ON/OFF discrete but there is no visual feedback to the switches.
(b)
Command Engage Sequence Detection Logic
1) Each FCC receives CMDENG REQUEST ACCEPTANCE logic from the other two FCCs via the cross-channel bus and records the order in which each become CMDENG. One of the discretes (L FIRST, C FIRST, R FIRST) is supplied to the first-in-command detection logic. This logic determines which FCC will supply FMA signals to the EFIS. It identifies LOCAL FIRST IN COMMAND and FOREIGN channels during multi-channel engage (MCHENG). On detection of a failure in the first-in-command channel, the fail sequence logic selects a different channel to be first-in-command.
(c)
Autoland Processing Logic
1) The APP mode request generates the APPROACH ARM logic when the F/D disengage logic is zero. This is applied to the localizer logic as an alternate to the LOC mode arm logic (bubble B on the illustration), and is also used in autoland logic.
2) When APP ARM, MCHENG, Runway alignment enable, and IN-AIR are all logic one, the generation of runway align engage logic is enabled. This logic goes high when roll attitude is less than 10 degrees, delta runway track is less than 2 degrees and the LOC LINEAR logic has been generated. Runway align enable logic enables the runway alignment command processor. This logic one is latched after 2 seconds to prevent loss of the signal due to out-of-tolerance inputs that would cause a zero logic from the preceeding AND gate. The runway align engage logic also produces the delta runway engage and delta runway path logic.
3) When radio height is less than five feet, Rollout logic is produced and runway alignment logic goes to zero. The delta runway engage and delta runway path logic remain logic ones.
(24) Autoland Mode Control Signal Flow (Fig. 11)
(a) Rollout Arm Conditions
1) Delta heading runway is synchronized to adjusted heading and is zero. Delta LOC deviation distance is synchronized to filtered LOC deviation distance and is also zero. The rudder servo command is synchronized to zero to maintain the rudder crossfeed command at zero so that the runway alignment roll command will be held at zero.
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(b) Rollout Engage 1) At multi-channel engage, command equilization must occur to ensure that all FCCs deliver identical value commands to the flight control systems. All FCCs are synchronizing to rudder position. 2) The first channel in command engages into AUTOLAND CMD as soon as any other channel has a command request accepted. Any difference between servo actuator position and rudder position is the rudder equilization command (normally very small) and is routed to the max/min selectors. The max/min feature prevents excessive deflection from the rudder's present position. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 自动飞行 AUTOFLIGHT 1(174)
