Which is an effect of an aerodynamically unstable aircraft?

An aerodynamically unstable aircraft is one that tends to deviate from its flight path without automatic correction by the pilot. In such situations, any small disturbances—like turbulence or control inputs—can lead to significant changes in attitude or performance. This instability means that the pilot must constantly make adjustments to maintain the desired flight path, which can lead to a higher workload and the potential for human error. Consequently, the risk of a crash is increased because the aircraft is less forgiving in terms of control response and recovery from disturbances.

While some level of aerodynamic instability can be desirable for certain types of aircraft in specific conditions, in general aviation and commercial aircraft, a greater instability can result in more difficult handling characteristics and a heightened likelihood of accidents if not expertly managed. The effect of an unstable aircraft is not found in options that suggest improved control responsiveness, smoother flight, or better performance, as these all rely on a certain degree of stability for safe and efficient operation.