In what scenario is an aircraft's emergency electrical system activated?

The activation of an aircraft's emergency electrical system is primarily designed to provide power when there is a failure in the primary electrical system. This scenario ensures that critical flight instruments and systems remain operational even when the main power source is compromised. The emergency electrical system typically supplies power to essential systems, such as navigation, communication, and flight controls, allowing the pilot to maintain control of the aircraft and execute emergency procedures if necessary.

In contrast, routine maintenance checks and pre-flight inspections focus on ensuring that systems function correctly before flight rather than responding to a failure. Switching to auxiliary power is a normal operational procedure to provide additional power but does not necessarily indicate a failure in the primary system; it is often a preventative measure or a transition to a backup source. Therefore, the scenario of a primary electrical system failure directly correlates with the necessity and activation of the emergency electrical system.