Safety Correlation between
the Generators and Batteries

7 generators installed on the 787(including for emergency use)

All necessary electric power for the 787 during flight is generated and supplied by generators installed on both engines.

Two generators are installed on the right and left engines of the main wings respectively, that is, a total of 4 generators. They supply all the necessary electric power during flight. Furthermore, two generators are installed on the auxiliary power unit (APU) to back up in the event of engine generator malfunctions. And in the rare event that all six of these generators malfunction, a wind turbine generator is installed for emergency use. (normally installed inside the fuselage and deployed outside the aircraft in an emergency.)

Two batteries

Besides these 7 generators, the 787 has two primary lithium-ion batteries. They are both the same, but one is for the main battery and the other is for the auxiliary power unit (APU). Their main purpose is explained below.

[Main battery]

  • Powers up the aircraft when it is parked on the ground, the engines or APU is turned off, the generators are not moving, and the aircraft is not connected to the aircraft ground power unit (GPU) (electric power unit supplied at airport).
  • In the event that all 7 generators malfunction and power from the generator cannot be supplied, it backups and supplies power to the aircraft.

[APU battery]

  • Supplies power to the starting motor when the aircraft is parked on the ground, the engines or APU is turned off, the generators are not moving, and the aircraft is not connected to the aircraft ground power unit (GPU) (electric power unit supplied at airport).
  • Supplies power to the controlling device when the APU is in use.