Battery Switch

• ON - On an unpowered airplane on the ground, turns on several switch annunciator lights and allows the APU to be started. No displays units are powered. Inflight or on the ground when AC power is removed, the following are powered:
  • Standby busses
  • Emergency lighting
  • Left inboard display
  • Left out board display
  • Upper center display
  • Left CDU
  • Captain's radio tuning panel
  • Forward three audio control panels
  • PA system
• OFF - Turns battery power off on the ground only (inhibited in flight). In flight, an EICAS message appears.

APU Generator Switch

• ON - Arms APU generator breaker to close automatically.
• OFF - Opens APU generator breaker.
• Light - Comes on with APU running to indicate one of the following:
  • Generator breaker is open due to a fault
  • APU GEN switch is selected OFF

Auxiliary Power Unit (APU) Switch
The APU supplies the plane with Bleed Air and Electrical power, and is located in the tail cone of the airplane. It is certified for in-flight start and may be operated to the airplane's maximum certified altitude.

• APU Selector
  • OFF - Closes APU bleed air isolation valve, initiates normal shutdown and resets auto shutdown fault logic.
  • ON - Opens APU fuel valve and inlet door, activates AC or DC fuel pump and powers APU controller.
  • START - Initiates automatic start sequence and spring loaded from START to ON.
• APU Fault Light - Indicates one of the following:
  • APU fault and/or fire
  • APU shutdown due to fault and/or fire
  • APU controller self-test

Left & Right Bus Ties

• AUTO - Arms the respective automatic AC bus tie circuits.
• ISLN - Opens the respective bus tie breaker.
• ISLN Light - Indicate the bus tie breaker is opened by the switch or a system fault.

Primary & Secondary External Power Switches

• EXT PWR Switches - Control external power to the busses. If pushed with AVAIL light on, close external power contactor. A second push disconnects external power. Without engine or APU generator power, the battery switch or primary external must be on for secondary power to connect to the bus(ses).
• ON Lights - Indicate external power is connected to the bus(ses).
• AVAIL Lights - Indicate external power is plugged in and voltage and frequencies are within limits. Goes off when the ON light comes on.

Left & Right Generator Control Switches

• ON - Arms generator breaker to close automatically when generator power is available.
• OFF - Opens generator field and breaker. Resets fault trip circuitry.
• OFF Lights - Indicate respective generator breaker is open.

Left & Right Drive DISC Switches (Guarded)

• DRIVE - Disconnect respective IDG from the engine. (Maintenance action on the ground is required to reconnect.)
• DRIVE Light - Indicate low IDG oil pressure.

Left & Right Backup Generator Switches

• ON - Arms backup generator operation.
• OFF - Opens backup generator control relay and resets fault circuitry.
• OFF Lights - Indicate a backup generator failure, a circuit fault or the switch is off.