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Wake Turbulence—An Obstacle to Increased Air Traffic Capacity 5 Findings and Recommendations A complete list of the committee’s findings and recommendations appears below, in the order in which they appear in the report. Finding 1-1. Air transportation system capacity could be significantly enhanced by applying the results of robust and focused wake vortex research and development. These results will be required in order to use the system at its maximum efficiency. Recommendation 1-1. Aircraft wake vortex characteristics of transport airplanes operating in the national airspace system should be assessed using the best standardized techniques prior to their introduction into service, so that appropriate separation criteria may be established with regard to each new aircraft model. The details of this assessment should vary based on the impact any new aircraft is expected to have on the system, with large and heavy aircraft receiving more emphasis than small ones in terms of data requirements. Finding 2-1. There is no champion, spokesperson, or leader held accountable for goal achievement across the nation’s wake turbulence research and development efforts. Finding 2-2. Wake turbulence is a long-term problem. Although a total solution cannot be achieved within a decade, improvements will become available gradually, depending on funding, and it can be envi-
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Wake Turbulence—An Obstacle to Increased Air Traffic Capacity sioned that these incremental improvements will provide incrementally increased capacity at airports where implemented. Recommendation 2-1. Federal wake turbulence research should have the following characteristics: The FAA should be the lead agency for defining requirements for wake turbulence research. The FAA should manage and fund capacity-focused wake turbulence research using academic, industry, and other government partners. The FAA should appoint a strong and motivated leader to integrate and coordinate research across agencies, define priorities, and represent wake vortex research to the JPDO and other agencies. Research should be sustained over the short, medium, and long term. Resource allocations across functional lines of involved agencies should be coordinated among all agencies involved in this work. Finding 2-3. The change in aeronautics research priorities at NASA has led to a gap in the wake turbulence program as previously envisioned. Finding 2-4. Present federal investment does not place sufficient priority on wake turbulence research to achieve the results called for by the NextGen goals. Finding 2-5. NASA expertise is well-aligned to conducting medium- to long-term fundamental research, including wake vortex modeling and wake vortex alleviation work, while the FAA does not currently have such expertise. Recommendation 2-2. Because of its expertise, NASA should continue to conduct medium- to long-term fundamental research, including wake vortex modeling and wake vortex alleviation work at a level of effort sufficient to achieve NextGen goals. Recommendation 2-3. Operators and controllers should be included in the process of designing, implementing, and evaluating wake turbulence-related changes to the air transportation system. Recommendation 2-4. JPDO should recommend to the FAA detailed wake vortex research efforts needed to support NextGen.
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Wake Turbulence—An Obstacle to Increased Air Traffic Capacity Finding 3-1. En route wake vortex issues may arise, especially for very light jets in cruise. Recommendation 3-1. The JPDO should investigate and define specific requirements for research on the impact of cruise-altitude-generated wakes on capacity (including climb and descent) to avoid future problems as fleet diversity increases. Finding 3-2. NextGen is expected to include separation management capable of permitting reduced and dynamic separation standards. Recommendation 3-2. JPDO should conduct a detailed analysis of what wake turbulence research and development is needed to achieve its separation management capability goals, and provide a detailed plan with milestones that will lead to successful development in the required time frame. Finding 3-3. Reducing the spacing needed to avoid wake turbulence will allow more efficient usage of existing runways. Recommendation 3-3. The FAA, assisted by NASA, should continue its current improved spacing programs, which promise results in the short and medium terms. Finding 3-4. In many airports, the use of dynamic wake vortex spacing standards could permit parallel runways to be built closer together, meaning that in some cases, new runways may be built between existing runways, or elsewhere on existing airport property. Recommendation 3-4. The FAA should pursue work in the short and medium terms to determine minimum runway spacing for future airport expansion, which is needed to achieve capacity goals in the long term. Finding 3-5. Onboard wake vortex visualization has been demonstrated in a proof-of-concept trial and can provide a safety net for dynamic spacing procedures. Recommendation 3-5. Wake vortex visualization concepts should be further explored and pursued. Finding 3-6. Vortex alleviation has the potential to significantly impact aircraft spacing requirements in the long term.
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Wake Turbulence—An Obstacle to Increased Air Traffic Capacity Recommendation 3-6. Vortex alleviation ideas, including configuration changes and active and passive forcing, should be explored. Finding 3-7. NASA’s aeronautics program is well-aligned to conduct wake vortex alleviation work as medium- to long-term foundational research. Finding 3-8. The Weather Research and Forecasting model currently in development can provide the necessary weather prediction resolution to support the needs of NextGen. However, as presently conceived the model lacks the ability to incorporate eddy dissipation rates and thus will not provide the optimal set of parameters for predicting wake turbulence. Recommendation 3-7. Federal wake turbulence research should engage the Weather Research and Forecasting model effort in order to identify the optimal set of weather parameters needed for predicting wake turbulence. Finding 3-9. European forecast models have demonstrated some short-term terminal area wake vortex forecast capability. Recommendation 3-8. Research should be done to ensure that weather modeling is adequate to predict wake vortex movement and decay. Finding 3-10. Wake vortex modeling is an essential element for most concepts aimed at reducing IFR spacing requirements. Finding 3-11. NASA’s aeronautics program is well-aligned to conduct medium- to long-term foundational wake vortex modeling. Finding 3-12. Research and development of high-resolution wake vortex measurement sensors to support wake vortex modeling efforts has stalled since the late 1990s. Finding 3-13. No high-resolution wake vortex measurement system capable of operating in inclement weather exists. Recommendation 3-9. Explore concepts for an all-weather, aircraft-based wake vortex measurement system that provides information on the location of the wake.
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Wake Turbulence—An Obstacle to Increased Air Traffic Capacity Recommendation 3-10. Develop an all-weather wake vortex measurement system that provides high-resolution measurements of wake vortex characteristics sufficient to validate wake vortex modeling. Finding 3-14. Although the current air transportation system was designed to avoid wake vortex encounters, they do occur and are safely tolerated using present spacing criteria. Finding 3-15. It is difficult to quantify acceptable reductions in wake turbulence spacing because there is no agreed metric for, nor definition of, hazard boundaries for wake encounters. Recommendation 3-11. A hazard boundary needs to be defined and used as a metric in forming spacing criteria. Finding 3-16. Implementing a system to gather data on wake events in the short term could establish a baseline that could be used to quantitatively evaluate potential solutions, as well as gain the support from the operator and ATC community that will be necessary to increase system capacity. Finding 3-17. System-level studies are an essential element of a wake turbulence research program. They are basic to ensuring that (1) research priorities will be set in a rational manner, (2) the actual realizable benefits of wake turbulence solutions will be known, (3) key constraints can be identified, and (4) NextGen capacity goals can be achieved. Recommendation 3-12. The current JPDO research in system-level modeling of the air transportation system should be continued and resources should be directed to extending simulation capabilities to cover a range of operational scenarios, weather scenarios, fleet mixes, and airport layouts. Recommendation 4-1. Wake turbulence research should pursue multiple tracks, with the goal of a robust, stable program that will provide continuing reductions in aircraft spacing as new ideas and technologies are developed and proven. Recommendation 4-2. Wake vortex research priorities should be periodically reexamined. Recommendation 4-3. The federal wake turbulence R&D enterprise should continue its relationships with a balanced mix of government laboratories, industry, and academia.