What is the function of the avionics bus isolation switch in a modern aircraft?

• A. It isolates the avionics bus for power management, testing, or fault isolation and may be controlled via an electrical control unit
• B. It connects the avionics bus directly to the battery
• C. It disconnects the entire electrical system from the airframe
• D. It powers the navigation radios only

Answer: (A)

The avionics bus isolation switch serves to energize or de-energize the avionics DC bus as a single controlled action. This lets maintenance or flight operations isolate the avionics for power management, fault isolation, or testing without cutting power to other non-avionics systems. In practice, the switch is often controlled by an electrical control unit, which can automatically isolate the bus if a fault is detected or during specific test sequences. This capability prevents a fault on the avionics bus from propagating to other power paths and allows safe re-energization once issues are addressed. It does not directly connect the avionics bus to the battery, disconnect the entire electrical system from the airframe, or power only a subset of radios.