(c)  
The Test Sync B signal is used during BITE testing to indicate that both FCC's are installed.

 (d)  
The angle of attack input is used primarily during takeoff and go around modes. It provides a reference to prevent the airplane from reaching stall conditions.

 (e)  
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.

 (f)  
The flap position is used to provide reference airspeed and angle of airflow programs for takeoff and go around mode operation.

 (g)  
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.

 (h)  
The landing gear lever switch & air ground relay signals are used in the takeoff mode logic as requirements for entering the mode.

 (i)  
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.

 (j)  
The N1 valid and N1 signal inputs are used in the stabilizer trim section of the DFCS.

 (k)  
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.

 (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 stabililzer position sensor provides information for use in the automatic stabilizer trim section of the DFCS.

 (n)  
The thrust lever Takeoff/Go Around (TO/GA) switches provide an input to the mode section for selection of the takeoff or go around modes.

 (o)  
The greater than 60 knot detector is the wheel spin logic which prevents entering the GA mode if wheel spin is detected.

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 ú ú 08 Page 80F ú Nov 12/01
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A
737-300/400/500MAINTENANCE MANUAL
 (p)  The EFIS and Attitude transfer relays provide an input to the FCC to indicate which IRU system is to be used. If a ground is provided the No. 1 system is used. If a ground is not provided the No. 2 system is used.
 (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 conjuction with the level change mode to display target speed or mach as determined by the FCC input.

 (b)  
The altitude alert aural outputs and altitude alert visual outputs provide aural and visual indications to the pilots when the airplane is approaching or deviating from the selected altitude.

 (c)  
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.

 (d)  
The elevator crossfeed (equalization) provides a signal to FCC B that represents the actuator position. These signals are used as combined feedback in the approach mode. The SPM fault A is a comparison between the A actuator and the elevator position sensor to determine when a allowable tolerances have been exceeded.

 R. Pitch Axis Digital Interface (Fig. 33)
 (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.

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