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B.  To release parking brakes, the captain's or first officer's brake pedals need only be fully applied and then released. A light on the control stand, next to parking brake lever, is provided to indicate when the parking brake is on.
CAUTION:  PARKING BRAKES SHOULD NOT BE SET FOLLOWING A HIGH ENERGY STOP. HIGH ENERGY STOPS ARE DEFINED AS A REFUSED TAKE OFF OR ANY STOP OTHER THAN NORMAL. UNDER STATIC PRESSURE, HOT BRAKE SURFACES TEND TO FUSE TOGETHER. THEREFORE, AFTER A HIGH ENERGY STOP, OR FOLLOWING TOUCH AND GO STOPS, A COOLING PERIOD OF 40 to 60 MINUTES FOR BRAKE UNITS SHOULD BE ALLOWED BEFORE THE PARKING BRAKE IS SET.
2.  Parking Brake Linkage
A.  The parking brake is controlled by a lever, hinged on top of the control stand. (See figure 2.) The parking brake linkage is shown in figure 2. When the parking brake lever is pulled, pawls swing toward the rudder pedals and engage the forward ends of bell cranks in the captains' brake linkage. The parking brake will not engage unless both brake pedals are depressed.
500 
May 15/67  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  32-44-0 Page 1 

H29213
Parking Brake System Location  500 
32-44-0  Figure 1  May 01/01 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

3.  Parking Brake Light
A.  The parking brake light is located on the control stand (Fig. 2). The light is a socket type with a red plastic translucent cover. When the parking brake is on, the outboard lever on the jackshaft operates a microswitch to illuminate the light on the pilot's control stand. Power for the light is taken from a 28 volt dc battery bus. A secondary light is provided in the ground service panel near the external power connector for use during ground operations. When the parking brake is applied, the microswitch also actuates the parking brake shutoff valve to prevent brake pressure loss to the return line through the antiskid valve.

591  Parking Brake Lever and Light 
Feb 15/80  Figure 2  32-44-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

4 Parking Brake Shutoff Valve
A.  The parking brake shutoff valve is installed in a common return line in the main wheel well between the four antiskid control valves and a system return line and prevents pressure bleed off when parking brakes are set. (See figure 4.)
B.  The parking brake shutoff valve is a 28 volt dc motor-operated ball-type valve. When parking brakes are set or released, the parking brake switch will actuate to energize the shutoff valve to closed or open position. (See figure 3.)
5.  Operation
A.  The parking brakes are set by depressing the brake pedals and lifting the parking brake lever and then releasing the brake pedals. The parking brake light will come on and remain on as long as battery power is on. To release the parking brakes, the brake pedals are depressed and released.

Parking Brake Shutoff Valve Circuit  522 
32-44-0  Figure 3  Feb 15/69 
Page 4 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

EFFECTIVITY
AS N730AS, N740AS, AS AND N742AS

591  Parking Brake System Schematic 
Aug 15/80  Figure 4 (Sheet 2)  32-44-0 
Page 5 

BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

PARKING BRAKE SYSTEM - TROUBLE SHOOTING
1.  General
A.  Trouble shooting the parking brake system should be performed whenever the brake accumulator pressure decays below the requirement stated in the parking brake system test (Ref A/T).
B.  The following precheck items should be performed before trouble shooting the parking brake system:
(1)  
Check that hydraulic brake system is bled and functioning properly (Ref 32-41-0 MP and A/T).

(2)  
Check that hydraulic accumulators are properly serviced (Ref 12-15-11, Hydraulic Accumulator Servicing).

2.  Parking Brake System Trouble Shooting
A.  Do the parking brake system bleed down test of Parking Brake System - A/T.
B.  If the parking brake bleed down rate is too high, do the trouble shooting as referenced in the Parking Brake System Trouble Shooting Chart.
3.  Parking Brake System Trouble Shooting Chart
501 
Oct 20/91  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  32-44-0 Page 101 

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