Which type of electrical bus is NOT typically found in an aircraft system?

The correct answer is Cooling bus. In aviation electrical systems, buses are used to distribute power to various components and systems throughout the aircraft. Common types of buses include a hot battery bus, which maintains power to critical systems even when the aircraft is not powered, an emergency bus that provides power to essential systems in the event of a failure, and an avionics bus dedicated to powering avionics equipment.

A cooling bus, however, is not a recognized or standard type of electrical bus in aviation. While cooling systems are critical in aircraft, especially regarding the thermal management of avionics and other systems, they do not have a dedicated electrical bus. Instead, cooling systems typically rely on other power sources or buses to function but do not require a unique electrical distribution bus for their operation. Therefore, recognizing that a cooling bus does not exist as a standard component of aircraft electrical systems makes it the correct choice in this context.