that assessment, based on the statement of task (see Appendix A) developed by NASA’s Aeronautics Research Mission Directorate and the NRC in accordance with the congressional direction. Chapter 5 lists all findings and recommendations; this summary highlights some of them.

WAKE TURBULENCE IS AN OBSTACLE TO INCREASED CAPACITY

The frequency of air traffic delays reached an all-time peak in June 2007, and that frequency is only expected to grow. The current air transportation system has reached a limit in certain airspaces, particularly near hub airports, where increasing traffic density and current routing practices necessitate a new approach to air traffic spacing and control. The interagency Joint Planning and Development Office (JPDO) was established to usher in the Next Generation Air Transportation System (NextGen). The seven entities represented in the JPDO are the FAA, the Department of Transportation (DOT), NASA, the Department of Homeland Security (DHS), the Department of Commerce (principally NOAA), the Office of Science and Technology Policy (OSTP), and the Department of Defense (DOD).

NextGen is expected to bring revolutionary changes in navigation, communications, and air traffic control, all designed to increase the capacity of the air transportation system. At most airports, this will mean more aircraft arriving and departing. Depending on their relative sizes, a certain minimum separation distance between aircraft must be maintained during approach and landing to avoid wake vortex encounters. Unless the separation distance can be reduced, other NextGen technologies will have much less impact on arrival and departure capacity than they otherwise could be expected to have.

When the Boeing 747 entered the airspace system in 1970, it was substantially bigger than the existing commercial aircraft. As a result, wake vortex separation criteria were developed based on then-available technology. Though there have been a few revisions to the criteria over the intervening years, the state of the art has not provided a basis for substantial changes. In many cases, these wake vortex separation requirements do not allow taking advantage of reduced separation standards enabled by satellite and other new technologies.

In the past, the focus of wake turbulence research was aimed at improving safety. Current wake vortex separation criteria are conservative and sufficient for ensuring safe operations. The key question now is whether a reduction in wake vortex separation criteria can be obtained while maintaining safety. Unfortunately, there is still no way to judge how much this spacing can be reduced—that is, there is no clearly defined



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