LANDING GEAR NORMAL OPERATION Of A320
EXTENSION
Description of the normal extension phase of the L/G.
DOOR OPENING
When DOWN is selected, the Landing Gear Control and Interface
Unit (LGCIU) takes control of the extension sequence. The LGCIU
signals the doors to open via selector valves and the door proximity
detectors signal the "doors fully open position" back to the LGCIU
in order to continue the sequence.
GEAR DOWN
When all doors are fully open, the LGCIU commands a gear extension
while maintaining the "doors open" signal. The gear proximity
detectors signal to the LGCIU that the gears are downlocked.
DOOR CLOSING
When all the gear are down and locked, the LGCIU signals the doors
to close and lock stay actuators to pressurize, while maintaining the
"gear extended" signal. Door closing hydraulic pressure is fed to the
lock stay actuators to back up the downlock springs. Door uplock
proximity detectors signal to the LGCIU that the doors are uplocked.
As the doors begin to close, the LGCIU cancels the "gear extended"
signal while maintaining the "door close" signal.
The extension sequence is completed.
RETRACTION
Setting the L/G control lever to UP causes systems 1 and 2 changeover.
This allows the system which was previously in standby to control the
next retraction and extension sequence. Each LGCIU controls one
complete gear cycle: one UP selection and one DOWN selection.
DOOR OPENING
The LGCIU must detect all three shock absorbers fully extended
before allowing the selection of the L/G control lever to UP. The
LGCIU signals the doors to open via selector valves and the door
proximity detectors signal the doors fully open position back to the
LGCIU in order to continue the sequence.
GEAR UP
When all doors are fully open, the LGCIU signals the L/G to raise
while maintaining the "doors open" signal to keep the doors "open"
line pressurized. The gear uplock proximity detectors signal the
LGCIU that the gear is uplocked.
HYDRAULIC SHUTOFF
Air Data Inertial Reference Units (ADIRUs) 1 and 3 send a signal to
the safety valve to shut off the hydraulic pressure to the L/G system.
When the airspeed is greater than 260 ±5 kts the hydraulic circuit to
the L/G is depressurized.
The retraction sequence is completed.
