What factors contribute to an aircraft's stall?

The correct answer highlights that exceeding the critical angle of attack is a primary factor leading to an aircraft's stall. The critical angle of attack is the angle at which the airflow begins to separate from the wing’s upper surface, resulting in a significant loss of lift. This phenomenon typically occurs when the aircraft is operated beyond its designed performance limits, causing the wings not to produce enough lift to maintain controlled flight.

Maintaining the angle of attack below this critical threshold is essential for safe flight operations. Pilots are trained to recognize the signs of an approaching stall and adjust the angle of attack accordingly to avoid reaching that critical point.

In contrast, the other choices do not directly relate to the aircraft's stall mechanism. For example, while inadequate fuel supply can impact flight safety, it does not inherently cause a stall. Similarly, flying at low altitudes and having excessive thrust may influence other aspects of flight performance but are not primary factors in causing a stall. Understanding the importance of the critical angle of attack is crucial for safe aircraft operation and stall prevention.