Electrics - Left AC Bus Failure 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 Shutdown Left Engine Shutdown 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
QRH If the Left BUS OFF light remains illuminated:

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

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

  • Left and Centre 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.

  • All Autopilots inoperative.

    Autopilot engagement requires at least two operable FCCs, as commands from the two FCCs are compared to prevent one FCC from commanding an autopilot hardover.

  • Flap Position Indicator inoperative.