(f)
The elevator position feedback signal is used as part of the synchronizing loop prior to engaging the pitch axis. It is also used as part of the system feedback during autoland.
(g)
The flap position is used to provide reference airspeed and angle of airflow programs for takeoff and go around mode operation.
(h)
The G/S super flag is monitored prior to and during approach. The G/S deviation provides the reference to maintain the airplane on the proper descent path during final approach.
(i)
The landing gear lever switch & air ground relay signals are used in the takeoff mode logic as requirements for entering the mode.
(j)
The neutral shift sensor provides information indicating the neutral position of the elevator with respect to the stabilizer. It is used as part of the normal feedback along with actuator position in all modes.
(k)
The N-1 valid and signal inputs are used in the stabilizer trim section of the DFCS.
(l)
The actuator position feedback signal is the prime feedback signal in the pitch axis. It is used in all modes of operation.
(m)
The Pitch Control Wheel Steering Force Transducer (PCWS) provides the command input to the pitch axis when the PCWS out of detent sensor is activated.
(n)
The stabililzer position sensor provides information for use in the automatic stabilizer trim section of the DFCS.
(o)
The thrust lever Takeoff/Go Around (TO/GO) switches provide an input to the mode section for selection of the takeoff or go around modes.
(3) The following is a breakdown of the various outputs and their relationship to pitch axis operation.
(a) The airspeed valid, bug drive and voltage reference outputs are used in conjunction with the level change mode to display target speed or mach as determined by the FCC input.
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737-300/400/500MAINTENANCE MANUAL
(b)
The outputs to the FMA are supplied to visually inform the pilots of the operating mode or status of the FCC.
(c)
The altitude alert outputs provide visual and aural indications to the pilots when the airplane is approaching or deviating from the selected altitude.
(d)
The FCC provides an elevator actuator output command to actuate the detent pressure solenoid (No. 2 solenoid) after the actuator solenoid signal has been received and logic requirements are met. The elevator valve amplifier command provides the signal which causes actuator displacement and a command to the elevator.
(e)
The pitch flight director steering signal provides the command to the ADI pitch command bar to indicate pilot action required to satisfy mode requirements.
Q. Pitch Axis Digital Interface (Fig. 31)
(1)
The digital interface diagram illustrates the various LRU's which provide inputs to and receive outputs from the FCC. These signals are in ARINC 429 format and include validity, sign, address, and data information.
(2)
The IRU's provide six inputs to the FCC for use in the pitch channel. Pitch signals are from IRU No. 1 but can be switched to IRU No. 2 under a both on 2 condition. The pitch attitude and attitude rate are primarily used in the cruise modes. The remainder of the signals are used in the cruise, approach, takeoff, and go around modes.
(3)
The DADC provides several inputs. The uncorrected altitude and the baro corrected altitude are primarily used in the altitude acquire and altitude hold modes. The mach number is used in the mach trim system as well as in the pitch channel during the level change mode. The CAS and TAS signals are also used in the level change modes.
(4)
The MCP provides discrete inputs to indicate mode changes and also indicates when selectable parameters have been changed. These would include airspeed, mach, altitude, and vertical speed.
(5)
The FMC provides inputs which are used in the submodes of V NAV operation. These include altitude for the V NAV altitude acquire mode, V/S for the V NAV V/S mode, and FMC airspeed and mach for the FMC speed modes. The discretes input is used to inform the FCC of mode status.
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