contacts of the DOWN limit switches, through terminal 3,  to the DOWN solenoid positive terminal (upper left). The  negative side of the DOWN solenoid coil is connected to  ground through the gear selector switch. Remember, the gear  DOWN switches are wired in parallel and activated when  the gear reach the full-DOWN position. All three gears must  reach full-DOWN to shut off the gear DOWN motor. Also  note that the gear selector switch controls the negative side  of the gear solenoids. The selector switch has independent  control of the gear UP and DOWN motors through control  of the ground circuit to both the UP and DOWN solenoids. When the landing gear control circuit is sending a positive  voltage to the DOWN solenoid, and the gear selector  switch is sending negative voltage, the solenoid magnet is  energized. When the gear-DOWN solenoid is energized,  the high-current gear motor circuit sends current from CB1  through the down solenoid contact points to the gear DOWN  motor. When the motor runs, the hydraulic pump produces  pressure and the gear begins to move. When all three gears  reach the DOWN position, the gear-DOWN switches move  to the DOWN position, the three green lights illuminate, and  the gear motor turns off completing the gear-DOWN cycle.  Figure 9-97  shows the landing gear electrical diagram with  the current flow path shown in red as the gear moves to the  retract (UP) position. Starting in the top right corner of the  diagram, current must flow through CB2 in the control circuit  through terminal 1 to each of the three gear-UP switches.  With the gear-UP switches in the not UP position, current  flows to terminal 2 and eventually through the squat switch  to the UP solenoid electromagnet coil. The UP solenoid coil  receives negative voltage through the gear selector switch.  With the UP solenoid coil activated, the UP solenoid closes  and power travels through the motor circuit. To power the  motor, current leaves the bus through CB1 to the terminal  at the DOWN solenoid onward through the UP solenoid to  the UP motor. (Remember, current cannot travel through the  DOWN solenoid at this time since the DOWN solenoid is  not activated.) As the UP motor runs, each gear travels to the  retract position. As this occurs, the gear UP switches move  from the NOT UP position to the UP position. When the last  gear reaches up, the current no longer travels to terminal 2  and the gear motor turns off. It should be noted that similar  to DOWN, the gear switches are wired in parallel, which  means the gear motor continues to run until all three gear  reach the required position.  During both the DOWN and UP cycles of the landing gear  operation, current travels from the limit switches to terminal  2. From terminal 2, there is a current path through the gear  selector switch to the gear unsafe light. If the gear selector  disagrees with the current gear position (e.g., gear is DOWN  A device called an inverter is used to supply AC when needed  for light aircraft. Simply put, the inverter changes DC into  AC. Two types of inverters may be found on aircraft: rotary  inverters and static inverters. Rotary inverters are found only  on older aircraft due to its poor reliability, excess weight,  and inefficiency. The rotary inverters employee a DC motor  that spins an AC generator. The unit is typically one unit and  contains a voltage regulator circuit to ensure voltage stability.  Most aircraft have a modern static inverter instead of a rotary  inverter. Static inverters, as the name implies, contain no  moving parts and use electronic circuitry to convert DC to  AC.  Figure 9-98  shows a static inverter. Whenever AC is  used on light aircraft, a distribution circuit separated from  the DC system must be employed.  [Figure 9-99] Many modern light aircraft employ a low-power AC  electrical system. Commonly, the AC system is used to  power certain instruments and some lighting that operate  only using AC. The electroluminescent panel has become  a popular lighting system for aircraft instrument panels and  requires AC. Electroluminescent lighting is very efficient  and lightweight; therefore, excellent for aircraft installations.  The electroluminescent material is a paste-like substance that  glows when supplied with a voltage. This material is typically  molded into a plastic panel and used for lighting. A throttle switch is also used in conjunction with landing gear  circuits on most aircraft. If the throttle is retarded (closed)  beyond a certain point, the aircraft descends and eventually  lands. Therefore, many manufacturers activate a throttle  switch whenever engine power is reduced. If engine power  is reduced too low, a warning horn sounds telling the pilot to  lower the landing gear. Of course, this horn need not sound  if the gear is already DOWN or the pilot has selected the  DOWN position on the gear switch. This same horn also  sounds if the aircraft is on the ground, and the gear handle  is moved to the UP position.  Figure 9-96  shows the gear  warning horn in the bottom left corner.  The squat switch (shown mid left of  Figure 9-96 ) is used to  determine if the aircraft is on the GROUND or in FLIGHT.  This switch is located on a landing gear strut. When the weight  of the aircraft compresses the strut, the switch is activated and  moved to the GROUND position. When the switch is in the  GROUND position, the gear cannot be retracted and a warning  horn sounds if the pilot selects gear UP. The squat switch is  sometimes referred to as the weight-on-wheels switch.  and pilot has selected UP), the unsafe light is illuminated.  The gear unsafe light is shown at the bottom of  Figure 9-96 .  AC Supply 9-55