Diamond DA 42 NG, Maintenance Manual

Page: 1374 / 2339

AIRCRAFT
Landing Gear
DA 42 NG AMM
Page 12
15 Mar 2018
32-30-00
Doc # 7.02.15
Rev. 4
C. Emergency Extension
Figure 7 shows the schematic diagram for the main landing gear emergency hydraulic extension
system. The pilot can use this system to extend the landing gear when there is a problem with the
normal extension system. You cannot retract the landing gear with the emergency system. The
emergency extension lever is located on the left side of the cockpit, below the instrument panel.
A flexible cable connects the emergency extension lever to the emergency extension valve. When
the pilot operates the emergency extension lever these events occur:
)
The emergency control lever opens the emergency extension valve. The actuating lever for the
emergency extension valve also operates a micro switch which isolates the electrical power
from the hydraulic pump. The pump cannot run.
)
Gravity causes the weight of each landing gear leg to move the piston in each actuator inwards.
The open emergency extension valve allows the fluid on the retract side of the piston in each
actuator to flow through the by-pass valves. The by-pass valves allow the hydraulic fluid flowing
from the actuators to by-pass the regulating valves and return to the reservoir. The position of
the solenoid valves does not affect the operation of the emergency extension system.
)
As each landing gear leg extends the related folding stay unfolds. Tension springs located in
each landing gear bay ensure that each folding stay fully unfolds. When the stay fully unfolds
the spring operated latching mechanism positively locks the folding stay open. The locked stay
holds the related landing gear leg fully extended.
)
When the folding-stays are locked, the related folding-stay switches (LDG GEAR DOWN) are
closed and electrical ground is supplied to the related green indicator lights. The electrical circuit
for the selected indicator light is closed and the green light illuminates.