Electrics - Battery Show Schematic only

DC Electrical System Airplanes with 90-minute standby power - The main and APU batteries are paralleled if power is lost at the left 28 volt DC bus. APU Battery main Battery Battery Switch Battery Discharge Lights Static Inverter Standby Power Selector Switch Standby Power OFF Light Hot Battery Buss Battery Bus Standby DC Bus Standby AC Bus Left Main DC Bus Right Main DC Bus Centre Buses As Installed Power will transfer providing at least 2 generators are operating and 3 autopilots armed for approach If there is a loss of power on one of the two DC buses, the DC BTB will close automatically. AC Electrical System Start APU Connect External Power Start Left Engine Start Right Engine AC Buses and Load Shed System Generator Drive Disconnect Generator Drive Disconnect AC Bus Tie System AC Bus Tie System Generator Control Switch Generator Control Switch Ground Service Switch Ground Service Bus Ground Handling Bus - The Ground Handling Bus can only be powered on the ground by the APU or External Power. It cannot be powered from the engine-driven generators Left AC Bus OFF Light Right AC Bus OFF Light Left Flight Instrument Transfer Relay Right Flight Instrument Transfer Relay Left AC Bus Right AC Bus Captain's Flight Instruments Transfer Bus First Officer's Flight Instruments Transfer Bus

When the Battery Switch is pushed ON and the battery is the only source of power on the airplane, all electrical system indicator lights become operative except the Battery Switch OFF Light and Utility Bus OFF Lights.

Total AC Bus Failure

QRH If Both BUS OFF lights remains illuminated:

  • Flight in icing conditions may result in some erroneous flight instrument indications.

    The Left Aux Pitot [Heat] is powered by the Right AC Bus. Additionally, on non-HDG aircraft, the Captain's Pitot [Heat] and Left AOA Heat are both powered by the Right AC Bus.

    The First Officer's Pitot [Heat] and Right AOA Heat are both powered by the Right AC Bus. Additionally, on non-HDG aircraft, the Right Aux Pitot [Heat] is also powered by the Right AC Bus.

  • All Flight Directors inoperative.

    Although the Centre FCC (which provides Flight Director inputs) is powered by the Centre AC and DC Buses, in normal flight - non-autoland - the Centre AC and DC Buses are powered by the Left AC and DC Buses. Thus loss of Left AC also removes Centre AC.

    The Right FCC is powered by the Right AC and DC Buses.

  • All Autopilots inoperative.

  • Automatic Speedbrakes inoperative.

  • Antiskid for outboard wheels inoperative.

    Although antiskid for the inboard wheels is powered by the Battery Bus, the outboard wheels are powered by the Left and Right DC Buses.

  • Flap Position Indicator inoperative.

    For HMG equipped airplanes, the flap indicator is powered by the Left AC Transfer bus. The Left AC Transfer bus is powered by the Hydraulic Motor Generator when there is a loss of both left and right AC buses in flight.