What wake turbulence separation must be applied for aircraft making an instrument approach behind a heavy aircraft?

When considering the effects of wake turbulence, especially in the context of aircraft making instrument approaches behind a heavy aircraft, the appropriate separation is crucial for safety. Heavy aircraft, such as large airliners or cargo planes, generate significant wake turbulence due to their size and mass.

The correct requirement is that when an aircraft is making an instrument approach behind a heavy aircraft, a separation of 4 miles is mandated. This distance is essential to ensure that the following aircraft does not encounter the powerful vortices that can linger in the air after the heavy aircraft has passed. These vortices are particularly strong and can affect smaller aircraft significantly, potentially leading to loss of control if they fly through them too closely after the heavier aircraft.

In contrast, the other separation distances listed do not apply to the specific conditions involving an instrument approach following a heavy aircraft, as they either specify incorrect distances or apply to different situations. The established standard of 4 miles helps maintain safe operations at airports, especially during approach phases when precision is paramount.