What is the function of the Start Bus?

The function of the Start Bus is primarily to distribute battery or external power. This is a crucial system in aircraft operations, particularly during the start-up sequence when the aircraft needs to power various systems while the engines are not yet running. The Start Bus ensures that the essential avionics, lighting, and control systems receive adequate power supply either from the onboard battery or from external sources such as a ground power unit.

Ensuring a reliable power distribution means that the aircraft can start its systems effectively, without interruption or overload. This function is fundamental for safety, as any lapse in power distribution could impact the aircraft’s ability to monitor and operate key systems required for pre-flight checks and engine start procedures. The ability to utilize both battery and external power enhances operational flexibility in various ground situations.

While functions like battery charging, health monitoring, and controls for cabin lighting systems are important, they do not encompass the primary role of the Start Bus, which is centered around the reliable distribution of power at the start of operations.