22-11-01
 ú ú 05 Page 47 ú Nov 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (m)  Cross Channel Disengage
 1)  A cross channel disengage discrete is used in dual A/P engage only if FCC A is disengaged the discrete disengages FCC B. Likewise if FCC B is disengaged FCC A is disengaged.
 (2)  Stabilizer Trim Interlocks
 (a)  
The stabilizer trim motor is monitored with the following interlocks: 1) STAB TRIM motor speed valid. 2) A/P trim cutout switch in the normal position. 3) The main electric trim is not being used. (Relay R64 is

 energized when the main electric trim is activated.)

 (b)  
The stabilizer trim motor is a two speed motor. Two separate windings within the motor are used for speed control.

 (c)  
A relay within the servo motor transfers the three phase power to the servo motor. The relay is controlled by flap switch S245. Another switch (S290) monitors that the relay is in the proper speed position and provides STAB trim motor speed VALID logic to both FCCs.

 (d)  
The A/P trim cutout switch opens the control circuit to the auto stab trim motor. The A/P disengages if the switch is not in the NORMAL position.

 (e)  
The main stabilizer trim relay is energized by the stabilizer control switch on the control wheel. The main electric trim motor is used to trim the stabilizer. The autopilot is disengaged when the main electric trim is in use.

 C.  A/P Engage Interlock Table (Fig. 15)
 (1)  
The A/P Engage Interlock table displays the functions monitored by the DFCS. These functions are divided into three groups:

 (a)  
A/P unlock interlocks, the logic functions required to allow the A/P to be engaged to CWS or CMD.

 (b)  
A/P engage hold interlocks, the logic functions required to hold the A/P in CWS or CMD.

 (c)  
A/P disengage interlocks, the logic functions that provide a disengagement of the A/P.

 (2)  
The monitored functions are described by item:

 (a)  
Item 1 - The stab trim cutout switch must be in normal.

 (b)  
Item 2 - Pressing either main electric trim switches energizes the stab trim control relay (R64). This opens the interlock during trimming with the main electric trim.

 (c)  
Item 3 - The A/P stabilizer trim motor is a two-speed motor. The mach trim switch and the flap up switch provide control and interlock for the speed change. Both switches and speed change relay must be in agreement to provide proper logic. A one-second delay allows for transition without disengagement.

 (d)  
Item 4 - The aileron force limiter provides a variable stop for the control wheel during A/P operation. The mach trim switch and flap up switch provide control and interlock for each limit. A 3-second delay allows for transition without disengagement.

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 22-11-01
 ú ú 04 Page 48 ú Nov 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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 22-11-01
úú 08 Page 49 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.

SEE PITCH MODE DISENGAGE TABLE
DISENGAGES, CAN BE RE-ENGAGED IN ANY MODE EXCEPT APP MODE WITH FGN IN CMD
UNLOCK HOLD  DISENGAGE 
1. A/P STAB TRIM CUTOUT SWITCH NORMAL X  X 
2. MAIN ELECTRIC TRIM SWITCHES (NOT PRESSED) X  X 
3. A/P STAB TRIM MOTOR SPEED VALID (10 SEC) X  X 
4. AILERON FORCE LIMITER AUTHORITY LIMIT VALID (10 SEC)  X  X 
5. INTENTIONAL BLANK  X 
6. INTENTIONAL BLANK X 
7. A/P DISENGAGE SWITCH NOT PRESSED  X  X 
8. A/P AILERON HYD PRESSURE SWITCH - NO PRESSURE X 
9. A/P AILERON HYD PRESSURE SWITCH - PRESSURE WITHIN 3.5 SEC AFTER ACT DET SOL ENGAGED  X 
10. A/P ELEVATOR HYD PRESSURE SWITCH - NO PRESSURE X 
11. A/P ELEVATOR HYD PRESSURE SWITCH - PRESSURE WITHIN 3.5 SEC AFTER ELEV ACT DET SOL ENGAGED  X 
　
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