787 Electrical System

Aviation pioneers Orville and Wilbur Wright had a mission: Fly forward for as long as possible, maintain speed, land at a point at least as high as the takeoff point and carry one pilot. In December 1903, the Wrights did just that, flying 852 feet (260 m) in 59 seconds. 

Today, expectations are much higher. For example, as the world’s most advanced family of jetliners, the 787 Dreamliner is designed to carry as many as 290 passengers as far as 8,500 nautical miles (15,750 km) — a third of the way around the Earth.

So it’s no surprise that to meet today’s missions, airplane electrical systems have been transformed from the single electric spark the Wright Brothers needed to the highly engineered, redundant systems that make modern jet travel possible.

Airplane power basics
On an airplane, the electrical system produces, controls and distributes power to all the other systems that need it — flight deck displays, flight controls, in-flight entertainment and more. It’s much like the electrical system in your house, which carries electricity throughout the rooms to power your lights, television and so forth.

Unlike your house, though, the airplane generates electricity as it flies. Airplanes don’t fly on battery power. Generators on the engines make power in flight.

The traditional airplane: electrical and pneumatic systems
On a traditional airplane, power is extracted from the engines in two ways to power other airplane systems:
  • Generators driven by the engines create electricity.
  • A pneumatic system “bleeds” air off the engines to power other systems (e.g., hydraulics).

Modern jet engines are very efficient, but removing that high-energy air robs them of some energy. A pneumatic system means that the engines produce less thrust, so they must be bigger, work harder and use more fuel. The system also means more weight, fuel burn and maintenance due to the heavy ducts and equipment needed to manage that hot air.

The 787: A more-electric system
The 787 Dreamliner uses more electricity, instead of pneumatics, to power airplane systems such as hydraulics, engine start and wing ice protection. Benefits of the 787’s innovative, more-electric design include:
  • More efficient power generation, distribution and use — including new remote power distribution units, which reduce wiring and save weight (approximately 20 miles, or 32 km, less wiring than on the 767).
  • Better fuel efficiency — better for airlines and the environment.
  • Lower maintenance costs and fewer maintenance tasks.
  • Less drag and noise.

Because the 787 uses more electricity than do other Boeing airplanes, the 787 generates more electricity, via six generators: two on each engine and two on the auxiliary power unit (APU, a small turbine engine in the tail).

On the ground, the 787 can be started without any ground power: The APU battery starts the APU generators, which start the APU to power the engine generators, which then start the engines.

In flight, the four engine generators are the primary sources of electrical power; the APU generators are secondary. Power runs from the generators to four alternating current (AC) buses, where it is either distributed for use as is (235 V AC) or converted to what other systems need.

Other power sources for the 787 include the main battery, used primarily for brief ground operations and braking; the APU battery, which helps start the APU; and ground power, which can connect through three power receptacles. The main battery, APU battery and ram air turbine also are available as backup power in flight in the unlikely event of a power failure.

As with every Boeing airplane, the 787 includes many layers of redundancy for continued safe operation, and the electrical system is no exception. For example, Boeing has demonstrated that the 787 can fly for more than 330 minutes on only one engine and one of the six generators and land safely.

Safety is designed in
The Boeing Company works to a specific design philosophy so that designs meet or exceed federal regulations.

Boeing designs to preclude failure — that is, so that systems won’t fail. Then Boeing goes further, assuming failure will occur and designing for the proper protections. Boeing also designs so that no single failure will cause an accident; for example, by including redundant systems, separating systems in space and functions — so that the loss of one doesn’t cause the loss of another — and providing standby and protective systems.

The 787 completed 5,000 hours of flight testing and an equal amount of test time on the ground. That testing demonstrated that the airplane performs as designed. The 787 successfully completed the Boeing program to test and validate the design as well as the most robust certification program ever conducted by the U.S. Federal Aviation Administration. The 787 electrical system was certified along with the airplane on Aug. 26, 2011.