Under what condition is a spin considered a prohibited maneuver regarding the power management unit (PMU)?

A spin is considered a prohibited maneuver when the power management unit (PMU) is off because the PMU is essential for managing the engine and ensuring stable operation during critical flight maneuvers. The PMU assists in regulating engine parameters and providing proper power settings.

When the PMU is off, there is no electronic management of the engine, which could lead to an increased risk of engine failure or improper aircraft responses during critical phases like a spin. Engaging in a spin without the PMU's oversight diminishes pilot control and heightens the likelihood of a mishap, making it critical that pilots adhere to this prohibition.

In contrast, having the PMU on ensures the aircraft's systems are functioning correctly, supporting safe operation in various maneuvers. Additionally, the other conditions listed do not inherently pose the same risks associated with disabling the PMU during spins, which directly impacts engine response and aircraft stability.