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757 MAINTENANCE MANUAL
 AIR/GROUND RELAY SYSTEM - DESCRIPTION AND OPERATION
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 1.  General (Fig. 1)_______
 A.  The air/ground relays provide various airplane systems control in two independent air ground sensing systems (system 1 and system 2). Air/ground sensing is provided by inputs from the nose gear not compressed sensors, main gear truck tilt sensors, and truck positioner actuator hydraulic inlet pressure switches. The relays energize or de-energize to provide equipment functions in ground or air mode. On most functions, either system 1 or 2 is used. However, critical airplane function may use both systems for air/ground sensing.
 B.  When the airplane is on the ground (main gear trucks not tilted, nose gear shock strut compressed, and truck positioner actuator hydraulic inlet pressue switches open) or in the air (main gear trucks tilted, nose gear shock strut extended, and inlet pressure switches closed), the proximity sensors provide air/ground signal to a proximity switch electronics unit (PSEU). The PSEU converts sensor input into a signal output to the relay. The relay energizes or de-energizes to provide ground or air mode condition. Air/ground system 1 or air/ground system 2 each consists of a number of relays, nose gear not compressed sensor, and left and right main gear truck tilt sensors. All relays are 4-pole, double-throw, rated at 2 or 10 amperes.
 C.  GUN 051; The relays are located in P33, P36 and P37 relay panels in the main E/E compartment.
 D.  GUN 001-010 AND GUN 101-999; The relays are located in P36 and P37 relay panels in the main E/E compartment.
 2.  Component Details
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 A.  Air/Ground Relays (Fig. 2)
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 (1)  All system 1 and system 2 air/ground control relays are 4-pole, double-throw, 2 or 10 amp-rated, hermetically sealed relays with pin-type terminals for electrical plug connections. The relays energize or de-energize to provide a ground or air mode condition to the airplane. System 1 relays are located in P36 panel. System 2 relays are located in P37 panel.
 

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NOSE GEAR
STRUT (REF)  MAIN GEARTILT SENSOR
INPUT
INPUT
NOSE GEAR NOT 
COMPRESSED 
SENSORS 
PROXIMITY SWITCH 
ELECTRONIC UNIT 
OUTPUT 
AUTO SPEED BRAKES 
AUTO BRAKES 
RAT 
THRUST REVERSERS 
PITOT HEAT 
OUTPUT 
STALL WARNING 
RELAY 
CARGO DOOR  (EXAMPLE) 
FOOT HEATERS 
EXTERNAL POWER 
PACS 
FCC 
AIR/GROUND RELAY PANEL 
(EXAMPLE) 
AIRCRAFT SYSTEMS (EXAMPLE)  (P33, P36 OR P37) 
Air/Ground Sensing 
Figure 1 

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RELAY IN THIS PANEL INSTALLED ON SOME AIRPLANES, SEE COMPONENT LOCATION FOR APPLICATION
Air/Ground Relays Location Figure 2

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 (2)  
GUN 051;
 Relay K144, a system 1 relay, is in the P33 panel.

 B.  
Nose Gear Not Compressed Sensors (Fig. 1)

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 (1)  
　
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本文鏈接地址：757 AMM 飛機維護手冊 起落架 CHAPTER 32 - LANDING GEAR 1(26)