In which scenario would an aircraft demonstrate negative stability?

An aircraft demonstrates negative stability when it diverges further from its original position after a disturbance. In this context, negative stability refers to an aircraft's inability to return to its original position after being disturbed; instead, it moves away from that position. This means that if the aircraft experiences a disruption, such as a gust of wind or pilot input, it will not only fail to stabilize back to its original flight path but will actually continue to move further away.

This behavior is characterized by an increasing displacement from the equilibrium point, resulting in an unstable flight condition. For instance, if an aircraft is supposed to fly straight and level and then experiences a disturbance, a negatively stable aircraft will move away from its intended flight path, potentially leading to further control challenges for the pilot. Understanding this concept is crucial for flight instructors, as it emphasizes the importance of stability in aircraft design and handling characteristics, and helps in addressing how to manage flight control in an aircraft.