The electric power system chosen for the Boeing 777 is an example of the advances seen in response to market demands for superior performance and reliability. The main electric system includes two engine-driven integrated drive generators, a generator driven by the auxiliary power unit, three generator control units, and a bus power control unit. A backup electric system independent of the main system provides the redundancy of electrical sources equivalent to a three-engine airplane, considering the auxiliary power unit inoperative. Both systems are automated to minimize crew workload.The highly automated features of the 777 aircraft are enhanced by the equally sophisticated control units of the electrical power system. The state-of-the-art, microprocessor-based control units use a high-level software language to provide control and protection for the system, along with an elaborate built-in-test (BIT) capability.Each control unit has two-way communication through a newly developed ARINC 629 communication bus. In addition to providing monitoring and built-in test information to the central aircraft information management system (AIMS) computer, an automatic checklist in each unit reports the real-time status of all main ac electrical power system control switches across the ARINC 629 communication bus for display in the flight deck.