UAL433, a DC10, departs Runway 28R on an Academy One departure. DAL201, a MD81, is waiting to depart Runway 28L on a runway heading departure. The runways are 2,500 feet apart. the soonest DAL201 can start takeoff roll is ___.

• A. 2 minutes from UAL433's takeoff roll
• B. 3 minutes from UAL433's rotation
• C. 1 minute after DAL201's own takeoff roll
• D. 4 minutes from UAL433's takeoff roll

Answer: (B)

Wake turbulence separation on closely spaced parallel runways is the key idea here. When a heavy aircraft departs from one runway and another aircraft plans to depart the adjacent runway only 2,500 feet apart, the wake vortices from the heavy can affect the following aircraft. To minimize risk, a minimum time gap is required between the lead’s lift-off and the follower’s takeoff roll.

In this case, the leading aircraft is a heavy, and the following aircraft is a medium. For parallel departures with this spacing, the rule is to wait three minutes after the leading aircraft rotates (lifts off) before the follower begins takeoff. That’s why the earliest start for DAL201 is three minutes after UAL433’s rotation. The other options don’t fit because they either underestimate the required wake separation, refer to timing relative to the follower’s own takeoff, or require more than the minimum necessary.