(2)
Logic inputs can cause a A/P disconnect or provide mode logic.
(a) The following logic inputs will cause a disconnect of the A/P. However in some cases the system may be re-engaged: 1) A loss of hydraulic pressure (aileron detent pressure
switch - S774). 2) Movement of R67 attitude transfer relay 2 from normal. 3) Movement of R51 attitude transfer relay 1 from normal. 4) Loss of power to R3 power transfer relay.
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A 737-300/400/500MAINTENANCE MANUAL
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M154 VHF NAV 1 (E3-4)
Roll Channel Analog Interface Block DiagramFigure 25
F99071
(3)
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737-300/400/500MAINTENANCE MANUAL
5) Movement of R44 VHF nav transfer relay from normal. 6) Movement of R14 heading transfer relay from normal.
(b)
The VOR/LOC super flag input is required before either the VOR or the LOC beam can be captured.
(c)
The R315 ILS antenna relay indicates whether the rear or forward antenna has been selected. This is used only in the LOC mode logic. LOC capture can be accomplished with the rear antenna and the LOC mode pushbutton selected. However, to capture with the APP pushbutton selected, the relay must be in the LOC or FWD position. Both the LOC capture and LOC OC logic will be reset if the rear antenna is selected with the APP pushbutton selected. The ILS DC input from the VHF NAV receiver is required before a capture of the LOC beam can be accomplished.
(d)
The surface position monitor (SPM) input from FCC B makes a comparison of the feedback from the aileron actuator LVDT and the position of the aileron position sensors. These are actuated 15 seconds after the AOC mode logic is generated with dual channel control. Loss of this signal will cause a disconnect of the autopilot.
(e)
The detent pressure switch inputs from the aileron actuators are monitored as part of engage interlock.
(f)
The loss of the flag alarm input from the Radio Altimeter will
cause a disengage during the approach mode.Command input signals are used for computer or feedback control.
(a)
The VOR/LOC deviation input is the prime guidance signal used during the two radio modes of operation. VOR deviation during a VOR mode and localizer deviation during a LOC or approach mode.
(b)
The aileron crossfeed input from FCC B provides a comparison of the aileron actuators (A and B) for use during approach.
(c)
The aileron actuator position feedback is a signal from the A actuator to indicate the amount of command received from the FCC valve amplifier and the actuators response.
(d)
The roll control wheel steering input is a command input signal used in the RCWS mode whenever the output of the "out of detent" sensor is exceeded.
(e)
The spoiler position feedback signal is summed with the aileron actuator feedback when the flaps are set at 27 degrees or greater.
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(f) The A/P-A/T radio altimeter drive signal is used during approach for gain control, flare control, GA logic, and dual engage logic.
(4)
Logic outputs provide annunciation, engage sequence, F/D control and bar bias plus self test inhibit.
(a)
The nine mode outputs provide grounds to enable visual displays on the flight mode annunciator as to the mode or status of the A/P or F/D system.
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