29-20-00 HYDRAULIC POWER- EMERGENCY SYSTEM Back

A. System Function

The emergency hydraulic system has two functions:

To supply the hydraulic power to extend the landing gear and the flaps, through their emergency systems (the emergency mode).
To supply the hydraulic power (while the aircraft is on the ground) to operate the aircraft systems for maintenance procedures (the normal mode).

B. System Operation (Ref. Fig. 1)

The hand-pump pressurizes the hydraulic fluid, which is supplied from the emergency cell of the hydraulic reservoir. The filter removes some of the contamination from the pressurized hydraulic fluid. The Emergency-Return Check Valve (ERCV) prevents the flow of hydraulic fluid from the park-brake return line, into emergency landing-gear circuit (of the auxiliary hydraulic system). The selector valve connects the pressurized hydraulic fluid (from the hand-pump) to one of these systems, the:

Main hydraulic system
Emergency extend system of the flaps
Emergency extend system of the landing gear

The check valve prevents the flow of pressurized hydraulic fluid, from the normal hydraulic system, into the emergency hydraulic system. The system must not be used in the normal mode while the aircraft is in flight. When the aircraft is in flight and the main hydraulic system does not operate, the emergency system is used to:

Extend the landing gear
Set the flaps to the 25 degree