N18NC, a LJ20, departs Runway 28R from the approach end. N56CD, a BE58, is waiting to depart Runway 28R at Charlie. What is the required wake turbulence separation?

• A. 3 minutes from N18NC's rotation
• B. 2 minutes after N18NC's rotation
• C. 3 minutes after N18NC's takeoff roll
• D. 5 minutes from N18NC's rotation

Answer: (A)

Wake turbulence separation is required when a following aircraft uses the same runway after a preceding departure. The amount of time to wait depends on the weight categories of the lead and follower, and for many common departures the reference point for counting the separation is the lead aircraft’s rotation (liftoff), not the moment it starts rolling.

In this case, a light jet leads and a light twin follows on the same runway. The required buffer for this pairing is three minutes, counted from the lead’s rotation. That means the trailing BE58 cannot depart until three minutes have passed since N18NC lifted off, ensuring the lingering wake from the lead has dissipated enough for a safe climb.

The other options don’t fit because two minutes is too short for this lead-follower combination, counting from rotation is the standard reference rather than from the takeoff roll, and five minutes is longer than needed for this pairing.