What is the required separation when a heavy aircraft is behind another heavy aircraft due to wake turbulence?

When a heavy aircraft is following another heavy aircraft, the required separation to mitigate the effects of wake turbulence is crucial for maintaining safety. The correct choice indicates that a separation of 4 miles is necessary in this scenario. This distance is established to ensure that the trailing aircraft avoids the wake turbulence generated by the lead aircraft, which can pose a risk of loss of control or changes in flight path.

Wake turbulence from heavy aircraft is particularly strong due to their size and weight, creating rotors of turbulent air that can extend for several miles behind them. By enforcing a separation of 4 miles between two heavy aircraft, air traffic control helps pilots maintain a safe distance, allowing sufficient time and space for the trailing aircraft to adjust for any potential disturbances caused by the wake of the lead aircraft.

The other options do not provide a sufficient buffer against the effects of wake turbulence when it involves heavy aircraft, which is why they are not appropriate choices in this context.