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## Landing Gear Transfer Unit 

The purpose of the landing gear transfer unit is to supply the volume of hydraulic fluid needed to raise the landing gear at the normal rate when system A EDP is lost. The system B EDP supplies the volume of hydraulic fluid needed to operate the landing gear transfer unit when all of the following conditions are met: 

• Aircraft airborne. 

• No. 1 engine rpm drops below a limit value. 

• Landing gear lever is up. 

• Either or both main landing gear not up and locked. 

## Standby Hydraulic System 

The standby hydraulic system is provided as a backup if system A and/or B pressure is lost. The standby system can be activated manually or automatically and uses a single electric ACMP to power: 

• Thrust reversers 

• Rudder 

• Leading edge flaps and slats (extend only) 

• Standby yaw damper 

## Indications 

A master caution light illuminates if an overheat or low pressure is detected in the hydraulic system. An overheat light on the flight deck illuminates if an overheat is detected in either system A or B and a low-pressure light illuminates if a low pressure is detected in system A and B. 

## Boeing 777 Hydraulic System 

The Boeing 777 is equipped with three hydraulic systems. The left, center, and right systems deliver hydraulic fluid at a rated pressure of 3,000 psi (207 bar) to operate flight controls, flap systems, actuators, landing gear, and brakes. Primary hydraulic power for the left and right systems is provided by two EDPs and supplemented by two on-demand ACMPs. Primary hydraulic power for the center system is provided by two electric motor pumps (ACMP) and supplemented by two on-demand air turbine-driven pumps (ADP). The center system provides hydraulic power for the engine 

