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MLG are held by their respective close / uplock mechanisms
Downlock Release
The landing gear lever is equipped with a solenoid lock, which prevents UP selection
of the landing gear lever with the airplane on the ground. After takeoff, if the solenoid
lock or a PSEU malfunction occurs, a downlock release button (DN LCK REL) on the
landing gear control panel can be used. Pressing the DN LCK REL button
mechanically withdraws the solenoid lock permitting UP selection of the landing gear
lever.
LANDING GEAR / BRAKES
For Training Purposes Only
May 03
15-7
P I LOT T R A I N I N G GU I D E
Normal Gear Extension
Figure 15-4
NOSE LANDING
GEAR SELECTOR
VALVE
NLG DOORS
SELECTOR VALVE
NOSE LANDING
GEAR DUMP
VALVE
NLG DOORS
DUMP VALVE
NLG DOOR
UPLOCK
NLG DOOR
ACTUATOR
NLG
UPLOCK
NOSE LANDING
GEAR ACTUATOR
NLG
DOWNLOCK
MAIN GEAR
SELECTOR
VALVE
MAIN GEAR
DUMP VALVE
LH MAIN GEAR
ACTUATOR
LH MAIN GEAR
UPLOCK
RH MAIN GEAR
ACTUATOR
RH MAIN GEAR
UPLOCK
LH MAIN GEAR
DOWNLOCK
ASSIST
ACTUATOR
RH MAIN GEAR
DOWNLOCK
ASSIST
ACTUATOR
MAIN GEAR
DOWNLOCK
ASSIST
SELECTOR
VALVE
ACCUMULATOR ACCUMULATOR
NO. 3 HYDRAULIC
SYSTEM
NO. 2 HYDRAULIC
SYSTEM
PSEU
LANDING GEAR CONTROL
• NLG DOWNLOCK
• NLG UPLOCK
• NLG DOOR UP
• MLG DOWNLOCK
• MLG UPLOCK
P604_15_009
MUTED
OFF
TEST
MLG BAY OVHT TEST
OVHT FAIL
UP DN
LDG GEAR
DN LCK
REL
ANTI-SKID
ARMED
NOSE STEER
ARMED
HORN
OFF
Legend
Commands
Pressurized
#3 System
Pressurized
#2 System
No Hydraulic
Pressure
LANDING GEAR / BRAKES
15-8 For Training Purposes Only
Jan 04
P I LOT T R A I N I N G GU I D E
Gear Extension
During gear extension, the NLG extends rearward and the MLG extend outward.
Maximum extension speed is 197 KIAS (0.6 M).
When the LDG GEAR handle is selected to the DN position, the PSEU commands and
monitors the following events:
• NLG door selector valve is energized to open the forward NLG doors
• NLG and MLG selector valves are energized to direct hydraulic fluid to release the
respective uplocks and extend the landing gear
• NLG and MLG downlocks are mechanically engaged to secure the landing gear in
the extended position
• NLG door selector valve is energized to close the forward NLG doors
• the hydraulic selector valves remain energized to provide full-time hydraulic
pressure on the NLG and MLG actuators and to hold the NLG door closed
The maximum airspeed at which the airplane may be flown with
the landing gear extended and locked is 250 KIAS (0.7 M).
If the landing gear position does not match the LDG GEAR
handle position within 28 seconds, the amber gear in transition
indication is replaced by the red gear not safe indication,
accompanied by the “GEAR DISAGREE” warning EICAS
message and aural warning.
NOTE
NOTE
LANDING GEAR / BRAKES
For Training Purposes Only
May 03
15-9
P I LOT T R A I N I N G GU I D E
Alternate Landing Gear Extension
Should a failure occur with the landing gear control circuitry or hydraulic system 3,
landing gear extension is still possible by pulling the red landing gear manual release
handle.
Pulling the handle mechanically releases the nose gear forward door uplock and the
three landing gear uplocks. In addition, the handle operates dump valves that remove
hydraulic pressure, allowing the gear to free-fall.
The nose doors open as the landing gear free-falls under its own weight. The nose gear
extends rearward and is assisted to the down-and-locked position by two downlock
assist springs (which lock the drag brace) and by the airflow pushing against the gear.
The nose doors will remain open.
The MLG free-fall to the extended position. The main landing gear are assisted to the
down-and-locked position by the MLG downlock assist actuators which are powered
by hydraulic system 2. The MLG downlock assist actuators force the MLG actuators
to full extension, which engages the internal downlock mechanisms.
A ball-detent retains the landing gear manual release handle in the extended position.
To reset the handle, the button in the center of the handle must be depressed and the
handle lowered to the stowed position.
To ensure priority to the primary flight controls, a spring-loadedclosed
　
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