Which parameter does the PMU adjust to avoid stress on the propeller during spins?

The correct response revolves around the ability of the Power Management Unit (PMU) to regulate the N1 speed in order to maintain it above 80% Np when the aircraft is in a spin condition. N1 refers to the speed of the engine's low-pressure turbine, while Np represents the propeller speed.

During spins, there is a significant risk of the propeller experiencing undue stress, which could potentially lead to mechanical failure. By maintaining the N1 above the predefined threshold, the PMU ensures that the propeller speed stabilizes, thus preventing over-speed or excessive blade angle that may occur if the propeller is subjected to extreme flight maneuvers. This protective measure allows for a safe and controlled flight environment while minimizing the risk of damage to the aircraft's propulsion system during critical phases like spins.

While oil pressure, fuel flow, and engine temperature are all important parameters in ensuring the smooth operation of the engine and propeller, they do not directly address the specific need to control propeller dynamics during spin conditions. Hence, the adjustment made to N1 by the PMU is crucial for maintaining both safety and aircraft integrity in those scenarios.