posted by 조근영만세 2018.01.11 05:35

B737NG Hydraulic system consists of 3 HYD System. Study yourself


*HYD A and HYD B have 2 pumps on each. one is EMDP(Electric Motor Driven Pump), EDP(Engine Driven Pump)

*STBY HYD has only one EMDP.

*Power Transfer Unit - In flight with HYD B EDP Fails, it will activate.

PTU valve opens only flaps 1 or 5 for 737-800, helps LEDs to operate

*Activating STBY HYD

1. Any of FLT CONTROL panel's switch to STBY RUD 


3. Lose of HYD A or B with flaps extended, above 60kts

*FLY CONTROL Switch (Guarded - ON)

 STBY RUD - Activate STBY HYD System and Standby rudder system. STBY RUD ON light will be illuminated

 OFF - Close Flight control Shutoff valve. so, blocks fluid towards to elevator, aileron, rudder.

 ON - Normal operating Position.

*LOW PRESSURE light illuminated - HYD A or B system pressure insufficient to control main control system. Extinguished if FLT CONTROL switch is positioned to STBY RUD

*LOW QUANTITY light - Always armed. illuminated when the pressure on STBY resorvior below 50%
*LOW PRESSURE light - Armed when the STBY system activated
*STBY RUD ON light - Illuminated when Standby rudder system activated


 OFF - normal position

 ARM - 

1.Closes Trailing Edge flap bypass valve, 

2.Activates stand by pump, 

3.arms ALTERNATE FLAP Position Switch

*ALTERNATE FLAPS position Switch

OFF - normal position

UP - Electrically retracts only Trailing Edge Flaps (Leading Edge Devices can not be retracted by this system)


1. Fully extends Leading Edge Devices

2. Electrically extends Trailing Edge flaps until released

HYD A's EDP, EMDP switch located on the left side of HYD Panel with LOW Pressure light on EDP, LOW Pressure light and OVERHEAR light on EMDP. 

*EDP switch normally on to prolong the solenoid life of the blocking valve

*LOW PRESSURE light illuminated - output pressure on the respective engine is low. However, This light inhibited when Fire handle pulled out

*OVERHEAT light illuminated - EMDP on the respective engine has overheated.

*Notify to ground personnel before pressurizing HYD.

*YAW DAMPER light illuminated - 

1. YAW DAMPER switch is OFF 

2. fault detected on SMYD(Stall Management/Yaw Damper System)

3. B FLT CONTROL SWITCH is positioned to OFF or STBY RUD

*In case of fault detected by SMYD, YAW DAMPER switch automatically moved to OFF

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