What supplies DC power in an aircraft?

The correct answer focuses on the role of TRUs (Transformer Rectifier Units) and various DC buses in supplying DC power within an aircraft. TRUs convert AC power, typically generated by the aircraft’s generators, into DC power that the aircraft's systems require for operation. This conversion process is essential because many avionics and electrical systems in an aircraft are designed to operate on DC power.

Additionally, the DC buses distribute this power throughout the aircraft, ensuring that various systems, such as lighting, communication, and emergency equipment, receive the necessary electrical supply. The integration of TRUs and DC buses ensures a reliable and continuous source of DC power for critical systems.

While generators do play an important role in generating electrical power, they primarily produce AC power. Batteries and external power sources contribute to the aircraft’s electrical system but are not the primary means of DC power supply compared to the comprehensive functioning of TRUs and DC buses.