Which of the following describes a prohibited spin?

A prohibited spin refers specifically to circumstances that create an unreasonable or unsafe condition for entering a spin. In this context, having flaps extended is particularly relevant because deploying flaps changes the aircraft's aerodynamic characteristics. When flaps are extended, the stall characteristics of the aircraft are altered, which can increase the likelihood and severity of a spin, making recovery more difficult.

Flaps are designed to enhance lift at lower speeds, but when in a spin, they can disrupt the airflow and control surfaces in a way that could prevent recovery from the spin. Therefore, flying with flaps extended during a spin situation is especially hazardous and is classified as a prohibited spin condition.

The other scenarios, while they may present challenging conditions, do not specifically pertain to the aerodynamics of a spin in the same way as flaps do. For instance, outside of controlled airspace or in a turn may not automatically result in a prohibited spin, and the PMU being set to auto pertains more to engine management rather than spin characteristics. Thus, the condition of having flaps extended is the key factor in identifying a prohibited spin in this question.