What happens to the Essential Bus when the battery master switch is turned on?

When the battery master switch is turned on, the Essential Bus is powered and turns on. The Essential Bus is a critical electrical system in various aircraft, responsible for supplying power to vital instruments, systems, and components required for safe operation. This functionality ensures that essential systems are operational even before the engines are started, allowing pilots to perform necessary checks and prepare for flight.

The other options, while they may describe actions that occur during different phases of aircraft operation, do not directly relate to the activation of the Essential Bus when engaging the battery master switch. The fuel pumps activating and the engine starting involve additional steps beyond simply powering the Essential Bus. Likewise, gauge resets would typically occur as part of the starting process or system initialization, rather than the mere act of turning the battery switch on.