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• The aircraft at or below 1,200 feet radio altitude and a power
lever retarded to 70% or less and all landing gear not down
and locked. The warning horn may be silenced in this
condition. If the power lever(s) is subsequently advanced to
more than 70%, the HORN SILENCE switchlight will
extinguish and the horn warning circuit will rearm.
• The flaps selected to more than 22° and all landing gear not
down and locked regardless of altitude. The warning horn
cannot be silenced and will sound until the aircraft
configuration is corrected.
B. Normal Retraction and Extension System
(1) Retraction Sequencing
(a) Landing gear lever is placed in UP position
(b) Red light in landing gear lever handle is illuminated
(c) Landing gear selector valve is moved to RETRACT position
(d) Hydraulic pressure is routed to OPEN side of landing gear
door actuators
(e) Landing gear doors open
(f) The timer valves route hydraulic pressure to the RETRACT
side of the main landing gear sidebrace actuators, unlocking
the internal downlock keys, and to the nose gear actuator and
release the nose gear downlock actuator
(g) The nose gear downlock actuator unlocks
(h) Three green DOWN AND LOCKED lights on landing gear
control panel are extinguished
(i) Landing gear retracts and locks into uplock hooks
(j) Hydraulic pressure is routed to CLOSE side of landing gear
door actuators
(k) Landing gear doors close
(l) Red light in landing gear lever handle is extinguished
(2) Extension Sequencing
(a) Landing gear lever is placed in DOWN position
(b) Red light in landing gear lever handle is illuminated
(c) Landing gear selector valve is moved to EXTEND position
(d) Hydraulic pressure is routed to OPEN side of landing gear
door actuators
(e) Landing gear doors open
(f) Hydraulic pressure is routed to UNLOCK side of landing gear
uplock actuators
(g) Uplock hooks unlock
(h) Hydraulic pressure is routed to EXTEND side of main landing
gear sidebrace actuators and nose landing gear extend /
retract actuator
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-32-00
Page 17
January 31/02
Revision 6
(i) Landing gear extends down and downlocks engage
(j) Three green DOWN AND LOCKED lights on landing gear
control panel are illuminated
(k) Red light in landing gear lever handle is extinguished
(l) Hydraulic pressure is routed to CLOSE side of landing gear
door actuators
(m) Landing gear doors close
C. Emergency Extension System
The landing gear emergency extension system will operate only if the
hydraulic lines for gear extension are intact. The system substitutes gas
pressure for hydraulic pressure to move the actuators of the landing gear
components. Emergency gear extension takes approximately six seconds
to extend and lock the landing gear. Emergency extension nitrogen
pressure will not close the landing gear doors after the landing gear are
down and locked, the gear doors remain open. Once activated, emergency
system pressure remains in the three actuators of each landing gear
(uplock release, door open and gear extend) until the pressure is vented
overboard when the emergency extension T-handle is stowed. Controls for
the emergency extension system are shown in Figure 9.
(1) Units and Components
(a) Nitrogen Bottle
Pressurized nitrogen used for emergency landing gear
extension is stored in a bottle located on the left side of the
nose wheel well. A fully charged bottle contains 150 cubic
inches of nitrogen pressurized to 3,000 psi at 70° F. The
bottle has a pressure relief valve set at 3,750 psi to prevent
damage to aircraft components should gas pressure exceed
the structural limits of the bottle. The location of the
emergency extension bottle is shown in Figure 10.
(b) Gear Emergency Extension Cable and T-Handle
The emergency extension T-handle is located on the forward
end of the copilot side console and is labeled EMER LDG
GEAR. The T-handle is connected by a flexible cable to the
pressurized nitrogen bottle. Pulling the T-handle to full
extension opens the bottle outlet valve, releasing
compressed nitrogen into the landing gear hydraulic lines. If
the emergency T-handle is subsequently returned to the fully
stowed position, the nitrogen bottle vent port opens, and
nitrogen pressure is discharged through an overboard vent.
(c) Dump Valves
Compressed nitrogen enters the hydraulic gear extension
lines through dump valves integrated into the normal
hydraulic system pressure lines. Nitrogen pressure activates
the dump valves to close off the normal hydraulic system
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