3.  Landing Gear Extension and Retraction
A.  Extension and retraction of the main and nose gear is by hydraulic power with a manual extension system for lowering the gear when hydraulic power is not available. The landing gear is controlled by a single control lever mounted on the pilots' center panel. Cables from a drum actuated by the control lever transfer motion to a selector valve that directs hydraulic pressure for gear actuation. A safety lock prevents the control lever from entering the UP position where conditions are not right for gear retraction.
B.  When the control lever is moved to the UP position, the gear retracts. When the main gears are fully retracted, a seal closes up against the main gear tire circumference. A special hubcap on the outboard wheel fairs the retracted wheel. The shock strut aperture in wing is closed by a shock strut door. A movable section of the shock strut doors carries a section of the seal to close off the upper portion of the tire below the shock strut. Mechanical linkage operates the shock strut door flap as the gear retracts and extends. Doors operated by a linkage connected to the nose gear close off the nose wheel well when the gear retracts. Moving the control lever to the DN position extends all gears. On extension, the nose gear doors open and remain open when the gear is down. With the control lever in OFF position, hydraulic pressure is released from all landing gear hydraulic lines and actuators. The gears are then held in the extended or retracted position by the mechanical locks. A tee handle actuates a crank and cable system for manual extension, which unlocks the gears and allows them to fall to the extended position by gravity. The nose gear doors are opened by mechanical linkage as the gear extends. When operated by the manual extension system, the gears free fall to the down and locked position.
C.  When the landing gear is to be retracted with the airplane on the ground, the airplane must be jacked and electrical and hydraulic power must be available.
4.  Landing Gear Position Indicating and Warning System
A.  In landing gear position indicating and warning system, a warning horn and indicator and warning lights provide indication for landing gear down and locked, landing gear not locked, and landing gear position not in accordance with control lever position.
504 
Jan 20/83  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  32-00 Page 5 

Air-Ground Sensing Functional Schematic  500 
32-00  Figure 4  (Sheet 1)  May 15/69 
Page 6 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

502  Air-Ground Sensing Functional Schematic 
Oct 20/83  Figure 4 (Sheet 2)  32-00 
Page 7 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

SYSTEM  SAFETY SENSOR FUNCTION  TO SIMULATE AIRPLANE-IN-AIR  PRECAUTIONS 
Drain mast heater  Provisions only 
Voice recorder Landing gear control lever lock Antiskid (inboard brakes) Wing anti-ice Stall warning  Permits erasure of tape after parking brake is set Prevents control lever from being placed in UP position when airplane is on ground Prevents application of brakes Before touchdown and loss of brakes at low speed Prevents hot air from entering anti-ice ducts When airplane is on ground Activates system when airplane is in air  Press and hold ground sensing test switch Cannot be simulated Press and hold air sensing test switch Press and hold ground sensing test switch Press and hold air and ground sensing test switches 1  None None None None Avoid contact with angle of airflow sensor vane as vane will be hot 
Flight recorder  Activates system when airplane is in air  Press and hold ground sensing test switch  If electrical power is being used, open flight recorder circuit breaker to prevent unnecessary operation of flight recorder. Close circuit breaker when maintenance is completed 

Air-Ground Sensing Functions  502 
32-00  Figure 5 (Sheet 1)  May 1/75 
Page 8 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

SAFETY SENSOR  TO SIMULATE 
SYSTEM  FUNCTION  AIRPLANE-IN-AIR  PRECAUTIONS 
Air conditioning turbo-fans Hydraulic system interconnect valve Electrical power Takeoff warning Cabin pressurization control Electrical system static inverter APU fire horn  Opens turbofan valves when airplane is on ground Permits hydraulic system interconnection after parking brake is set Prevents APU generator being switched from two busses (ground condition) to one bus (air condition) Prevents takeoff warning horn sounding when airplane is in air Maintains cabin pressurization when airplane is in air Prevents static inverter from draining battery on ground Prevents APU fire horn from sounding when airplane is in air  Press and hold ground sensing test switch Press and hold ground sensing test switch Press and hold ground sensing test switch Press and hold air sensing test switch Press and hold ground sensing test switch Press and hold ground sensing test switch Press and hold air sensing test switch  Check that air conditioning switches are off to prevent overheating air conditioning pack. Keep hand clear of ram air inlet deflector None None None None Place standby power switch on OFF position unless 115 volt ac power is available and equipment cooling blower circuit breakers are closed to prevent overheating static inverter None 
　
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