When departing behind a Category B or D on parallel runways separated by 2,500 feet, how many minutes must the second aircraft wait if flight paths will cross?

When departing behind a Category B or D aircraft on parallel runways separated by 2,500 feet, the standard procedure requires the second aircraft to wait for a minimum of 2 minutes before it can take off if their flight paths will cross. This is primarily based on safety considerations, ensuring there is enough time for the first aircraft to gain altitude and distance, thus avoiding any potential wake turbulence or separation issues when the second aircraft begins its departure.

The reason 2 minutes is the appropriate wait time in this scenario takes into account the characteristics of the Category B and D aircraft, which have specific climb rates and wake turbulence patterns that can impact following aircraft. Given a spacing of 2,500 feet, the air traffic regulations are designed to provide an adequate buffer, ensuring that the second aircraft has a safe departure without risking interference from the first aircraft's wake.

This regulation is established to uphold safety standards in air traffic control and to manage the complexities of flight operations, particularly in maintaining safe distances and vertical separation during the critical phases of takeoff and climb out.