What is the appropriate action to take when experiencing retreating blade stall?

When experiencing retreating blade stall, the recommended action is to lower the collective pitch and reduce forward speed. During retreating blade stall, the rotor blades that are moving away from the direction of flight (the retreating blades) experience a decrease in lift due to a reduction in angle of attack and an increase in induced flow. This can lead to a loss of control and a possible stall if not addressed promptly.

By lowering the collective pitch, the pilot reduces the overall lift generated by the rotor system, allowing the retreating blades to regain an appropriate angle of attack to produce sufficient lift. Additionally, reducing forward speed decreases the relative wind affecting the blades, which helps to prevent the stall condition from worsening. Slowing down allows the rotor system to operate more efficiently, particularly under conditions where retreating blade stall could occur.

This action is essential for restoring normal flight conditions and avoiding a more severe situation. It promotes better handling characteristics and ensures that the helicopter remains controllable as the pilot works to stabilize the aircraft.