Refer to figure.
Helicopter vortex ring state (VRS) is a dangerous condition that can occur when a helicopter descends too quickly in its own downwash.

When a helicopter descends rapidly (high rate of descent), the air flow below the rotor blades can become turbulent, causing a swirling vortex of air to form.

This vortex can then interact with the descending rotor wash, resulting in a rapid descent that is difficult to recover from.

Helicopter vortex ring state is characterized by a sudden loss of lift, yaw instability, and uncontrollable vertical descent.

Tail rotors are also susceptible to vortex ring state.

The reason is the same - “entry into the disturbed wake of the tail rotor”.

But the conditions are different. Rather than a high rate of descent it requires a high rate of yaw or apparent yaw.

For an anti-clockwise rotating main rotor with the tail rotor on the left of the tail boom, an airflow from the left can cause the vortex ring condition. This can occur with:

• Wind from the left,
• A high rate hover turn to the right or
• Sideways flight to the left