Which condition indicates an airplane is experiencing a stall?

A stall occurs when the airflow over the wings of an airplane is disrupted, primarily due to exceeding the critical angle of attack. The critical angle of attack is the maximum angle at which the wings can generate sufficient lift for the weight of the airplane. Beyond this angle, the smooth airflow separates from the wing's surface, leading to a significant loss of lift.

When the angle of attack increases beyond this critical limit, the aircraft can no longer maintain level flight, and it will consequently begin to lose altitude. This situation is characterized by a reduction in lift and can lead to an uncontrollable descent if not promptly addressed. Thus, recognizing that the stall is defined by this specific threshold of angle of attack is crucial for pilots, as it directly informs their maneuvering and recovery techniques during flight.

The other conditions do not lead to a stall and instead describe scenarios where the aircraft is still in a controllable state. For instance, a decreased angle of attack typically indicates that an aircraft is regaining lift, while maintaining steady airspeed during a climb does not suggest any stall condition. Moreover, an increase in thrust provided can be used to counteract a stall, rather than indicating one. Understanding these elements of aerodynamics is essential for safe flight operations.