detect when the gear reaches the full retract (UP) position.  Three down-limit switches are used to detect when the gear  reach the full extended (DOWN) position. Each of these  switches is mechanically activated by a component of the  landing gear assembly when the appropriate gear reaches  a given limit. and performs two functions (called a circuit breaker switch).  It should also be noted that the avionics contactor is often  referred to as a split bus relay, since the contactor separates  (splits) the avionics bus from the main bus.  Another common circuit found on light aircraft operates  the retractable landing gear systems on high-performance  light aircraft. These airplanes typically employ a hydraulic  system to move the gear. After takeoff, the pilot moves  the gear position switch to the retract position, starting an  electric motor. The motor operates a hydraulic pump, and the  hydraulic system moves the landing gear. To ensure correct  operation of the system, the landing gear electrical system  is relatively complex. The electrical system must detect the  position of each gear (right, left, nose) and determine when  each reaches full up or down; the motor is then controlled  accordingly. There are safety systems to help prevent  accidental actuation of the gear.  The landing gear system must also provide an indication to  the pilot that the gear is in a safe position for landing. Many  aircraft employ a series of three green lights when all three  gears are down and locked in the landing position. These three  lights are activated by the up- and down-limit switches found  in the gear wheel well. A typical instrument panel showing  the landing gear position switch and the three gears down  indicators is shown in  Figure 9-94 .  The hydraulic motor/pump assembly located in the upper left  corner of  Figure 9-95  is powered through either the UP or  DOWN solenoids (top left). The solenoids are controlled by  the gear selector switch (bottom left) and the six landing gear  limit switches (located in the center of  Figure 9-95 ). The three  gear DOWN indicators are individual green lights (center of  Figure 9-95 ) controlled by the three gear DOWN switches.  As each gear reaches its DOWN position, the limit switch  moves to the DOWN position, and the light is illuminated.  A series of limit switches are needed to monitor the position  of each gear during the operation of the system. (A limit  switch is simply a spring-loaded, momentary contact switch  that is activated when a gear reaches it limit of travel.)  Typically, there are six limit switches located in the landing  gear wheel wells. The three up-limit switches are used to  Landing Gear Circuit Figure 9-94.  Instrument panel showing the landing gear position switch and the three gear down indicators.  9-52