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AC BUS 1 & 2 ONLINE

System study · Electrical

Generators, Buses & the Emergency Chain

Two engine generators, an APU generator, batteries, and a RAT-driven emergency generator — all feeding a network of AC and DC buses. Click through the diagram, then quiz yourself on what happens when generators start dropping out.

Sources & buses click a component

Simplified — not for operational use. Click a generator, bus, or the batteries.
ENG 1 IDG · GEN 1 ENG 2 IDG · GEN 2 APU GENERATOR EXTERNAL POWER (GND) EMERGENCY GEN DRIVEN BY RAT/BLUE HYD AC BUS 1 AC BUS 2 AC ESS BUS DC BUS 1 / 2 DC ESS BUS BAT 1 / BAT 2 BRIDGE POWER BUS TIE LOGIC
Click any component above to see what it does →

The emergency electrical chain

LAST RESORT
ESSENTIAL BUSES ONLY

If both engine generators and the APU generator are lost, the aircraft briefly runs on battery power alone while the RAT deploys. Once the RAT is up to speed, it drives a hydraulic pump for Blue, and Blue pressure in turn drives the emergency generator, which powers the AC ESS and DC ESS buses — enough for flight instruments, radios, and basic flight controls, but not everything on the aircraft.

Quick reference

NORMAL GENERATION

  • IDG on each engine, one per side
  • Each feeds its own AC bus normally
  • Bus tie logic cross-connects if one fails
  • APU generator can substitute for either

DC SYSTEM

  • Powered via transformer-rectifiers from the AC buses
  • Two batteries provide short-term backup and buffer transients
  • DC ESS bus is the critical subset kept alive longest

ESSENTIAL BUSES

  • AC ESS and DC ESS carry only what's needed to keep flying
  • Automatically fed by the emergency generator if all else is lost
  • Batteries bridge the short gap while RAT spins up

Check yourself

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