What is a stall warning system and its purpose?

A stall warning system is designed to alert the pilot about an impending aerodynamic stall, which occurs when the airflow over the wings decreases to a point where the wings can no longer maintain sufficient lift. This critical function helps to ensure the pilot is aware of the aircraft's approach to a stall, allowing for timely corrective action to regain adequate control and avoid an accident. Such systems utilize various methods, including auditory signals or visual indicators, to provide real-time alerts, promoting safety during flight operations.

The other options mention various functions that are not related to stall warning systems. For example, indicators of fuel levels are concerned with managing fuel for flight but do not give any indication regarding the stall characteristics of the aircraft. Similarly, calculating optimal takeoff speed pertains to performance calculations rather than stall warnings. Lastly, irregular engine performance warnings are important for engine management but are distinct from stall alerts, as they do not directly relate to the aerodynamic state of the aircraft.