What is the critical angle of attack?

The critical angle of attack is defined as the angle at which airflow starts to separate from the wing's upper surface, leading to a significant loss of lift and the onset of a stall. When the angle of attack exceeds this critical value, the smooth airflow over the wing is disrupted, resulting in a turbulent flow that reduces the wing's ability to generate lift effectively. This phenomenon is critical for pilots to understand, as it determines the safe operating limits of the aircraft during maneuvers, especially when approaching or exceeding the stall condition.

The other options touch on concepts related to performance but do not accurately define the critical angle of attack. For example, while maximizing lift pertains to a different angle of attack before stalling occurs, it's not the critical angle itself. Similarly, the inability to climb is a result of exceeding several limitations, which may include but do not directly entail the critical angle, and maximum speed is unrelated to the angle of attack defined for stall conditions.