What is defined as a stall in aviation?

In aviation, a stall occurs when the angle of attack (AoA) of an aircraft exceeds the critical angle of attack. This angle is the point at which the wings can no longer generate sufficient lift to support the aircraft's weight. When a pilot exceeds this critical angle, airflow over the wings becomes turbulent, leading to a rapid decrease in lift. As a result, the aircraft can lose the ability to maintain altitude or, if not corrected, can enter a descent. Understanding this concept is crucial for pilots, as recognizing the signs of an impending stall and knowing how to recover from it are vital for safe flight operations.

The other choices relate to different flight phenomena or issues but do not accurately describe a stall: a loss of thrust pertains to engine performance, a sudden drop refers to a specific type of descent or issue rather than the aerodynamic principle of a stall, and mechanical failure indicates a breakdown in the aircraft’s systems rather than changes in airflow over the wings.