A concept for pairing departures from parallel runways for wake avoidance

Air traffic is expected to increase significantly over the next ten to fifteen years, doubling by some estimates. A major challenge for supporting this type of growth is the arrival and departure capacity at major airports. There are many initiatives working to improve the arrival capacities at these airports, but very few enable corresponding increases in the departure capacity. The MITRE Corporation's Center for Advanced Aviation System Development's (MITRE/CAASD's) research program is investigating a concept that could increase the departure capacity at fourteen of the thirty-five busiest United States airports. The "Paired Departure" concept increases the ability to use closely spaced parallel runways (CSPR) for departures by providing an alternate means of avoiding the wake turbulence created by departing Heavy and Boeing 757 (B757) aircraft. Currently, if parallel departure runways are spaced less than 2500 feet (ft) apart, a departing Heavy or B757 aircraft requires subsequent departures to wait two to three minutes to allow time for their wake to subside. This delay is required for both visual and instrument departures, regardless of wind direction and speed. Wake research over the past thirty years has developed a better understanding of wake movement and decay near the ground. By considering the spacing between the parallel runways at an airport and by establishing a maximum allowable crosswind, a wake-free departure time window can be defined such that it is not possible for a wake to transport to the other runway within that time interval. When a Heavy aircraft departs a CSPR runway, then an aircraft can start its departure takeoff roll on the parallel runway without incurring a wake delay until the paired departure time window expires (e.g., up until 30 seconds after the Heavy started its takeoff roll). A related departure procedure, Wake Turbulence Mitigation for Departures (WTMD)
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, is being developed by the Federal Aviation Administration (FAA). WTMD utilizes an accurate forecast of crosswind to determine when wakes will reliably be moved away from the parallel runway. No departure time window is required for a trailing departure with WTMD since the wake never reaches the parallel runway under the required crosswind conditions. The analysis performed to date shows that WTMD will likely be available from ten to thirty percent of the time at candidate airports with a potential to increase the departure capacity approximately ten percent or more during these times. The paired departure concept is intended to build upon the WTMD capability and to utilize the wind sensing and forecasting capabilities that are being developed to support WTMD. For airports that can implement the paired departure concept, the time that wake-free departures can be enabled could potentially be doubled due to the additional crosswind conditions that can safely be accommodated using the paired departure time window. This paper describes the paired departure concept, discusses key implementation options and issues, and provides results of an initial analysis of feasibility and potential benefit.