A B744 is executing a low approach on Runway 18, and a King Air is ready for takeoff on Runway 36 (opposite direction). The minimum separation required to clear the King Air for takeoff is ___ minutes.

• A. 3
• B. 2
• C. 4
• D. 1

Answer: (A)

Wake turbulence is the factor here. A heavy aircraft that is landing on one runway leaves strong vortices behind it that can drift into the path of other traffic, even if that traffic is operating on the opposite runway. In this scenario, the B747 on a low approach to Runway 18 can generate vortices that linger long enough to affect a King Air waiting to take off on Runway 36. To ensure the King Air avoids these hazardous vortices, you must provide a time buffer before the takeoff clearance. The minimum safe interval in this setup is three minutes. Shorter gaps risk encountering remaining wake, while a longer gap would be more than what’s required to maintain safety in most cases.