(d)  
Release the right pedal. 

(e)  
Slowly push the captain's right pedal forward until it touches the stop then release.

(f)  
As fast as possible, push the captain's left pedal forward. The left pedal should move smoothly forward until it touches the stop.  1) If the left pedal moves in the opposite direction of the applied force, replace the

rudder power control unit (Ref 27-21-91/401). 

(g)  
Release the left pedal.

(h)  
Slowly push the first officer's left pedal forward until it touches the stop then release.

(i)  
As fast as possible, push the first officer's right pedal forward. The right pedal should move smoothly forward until it touches the stop. 1) If the right pedal moves in the opposite direction of the applied force, replace the

rudder power control unit (Ref 27-21-91/401).

(j)  
Release the right pedal.

(k)  
Slowly push the first officer's right pedal forward until it touches the stop then release.

(l)  
As fast as possible, push the first officer's left pedal forward. The left pedal should move smoothly forward until it touches the stop. 1) If the left pedal moves in the opposite direction of the applied force, replace the

rudder power control unit (Ref 27-21-91/401).

(m)  
Release the left pedal.

(10)
Test yaw damper operation (Ref 22-11-0 A/T or 22-12-0 A/T).

(11)
Reconnect pushrod to nose wheel steering, if disconnected.

(12)
Restore airplane to normal hydraulic configuration (Ref 27-21-0).

(13)
Close all access doors and panels.

597 
27-21-0 Page 526  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/98 

G07048
502  Rudder Pedal Force Checking Tool 
Apr 01/97  Figure 507  27-21-0 
Page 527 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

RUDDER AND RUDDER TRIM CONTROL SYSTEM -DESCRIPTION AND OPERATION
EFFECTIVITY
AIRPLANES POST-SB 27-1252
1. General
A.  Yaw control of the airplane is provided by a single conventional rudder without tab. There are two separate hydraulic systems powering one main power control unit. Rudder control backup is provided by a standby power unit, which is driven by a third hydraulic system. Any one of the three hydraulic systems will provide effective rudder control. Rudder trim is accomplished by operating a trim control wheel which repositions the rudder.
B.  The rudder control system is pedal operated by the captain or the first officer (Fig. 1). Pedal movement rotates the forward quadrants, which are cable connected to the aft quadrant. Rotation of the aft quadrant moves a control rod which is connected to a torque tube. Rotation of the torque tube moves the two cranks connected to the main rudder power control unit linkage. This in turn admits hydraulic fluid to the actuating cylinder, which moves the rudder.
C.  Rudder trim is initiated by rotation of the trim wheel located on the aisle stand (Fig. 3.). The trim wheel is attached to the forward cable drum, which is connected by cables to the trim actuator located in the vertical fin. Extension or retraction of the trim actuator jackscrew causes the feel unit housing to rotate. This moves linkages which rotate the torque tube, causing rudder power control unit input.
D.  Rudder feel is provided by a rudder feel unit. The feel unit is connected to the rudder control torque tube, which connects through linkage and cables to the rudder pedals (Fig. 3.).
E.  The rudder is fully power operated through its entire travel. The main rudder power control unit is hydraulically operated by hydraulic systems A and B simultaneously. The A and B systems can be independently activated by switches located on the P5-3 overhead panel. Either of the A and B switches can be used to activate the standby hydraulic system, open the rudder standby system shutoff valve, and supply pressure to the standby actuator.
F.  System A pressure is supplied by two engine-driven hydraulic pumps, one being located on each engine. System B pressure is supplied by two electric motor-driven hydraulic pumps. A and B flight control hydraulic modular units are identical in components and operation. Pressurized hydraulic fluid flows through the modular unit which consists of a spoiler shutoff valve, a flight controls shutoff valve, low pressure warning switch, compensator, and check valve. The flight controls shutoff valve controls the flow of hydraulic fluid to the ailerons, elevator, and rudder. When either the A or B flight control switch on the overhead panel is moved to STBY RUD, or if the automatic standby function is activated, the standby hydraulic system pump will start. The standby rudder actuator shutoff valve located in the standby hydraulic module will also open, porting hydraulic fluid to the standby actuator.
　
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