ICAS 2002 Congress CAPACITY AND WAKE VORTICES J. N. Hallock US DOT Volpe National Transportation Systems Center Cambridge, MA C. Tung US Army Aero-Flight Dynamics Directorate, NASA Ames Moffett Field, CA S. Sampath US Army Research Laboratory, European Research Office London, UK Keywords: wake vortices, capacity, vortex behavior Abstract between aircraft using existing runways must be reduced. Aircraft wake vortices can pose a threat, The economic benefits of reduced wake especially in the terminal environment where turbulence separations at capacity-limited aircraft operate in close proximity. Vortex airports are substantial. Wake vortices limit in- separation standards preclude hazardous trail spacing between aircraft on approach, encounters, but are oftentimes very restrict the use of closely spaced parallel conservative. A key to increasing airport runways, and restrict departure and intersecting capacity is to know when vortices are not a runway operations. Research programs in the hazard so that aircraft can land and take off United States, Canada, and Europe have with closer intervals. A conference was held in endeavored to understand wake vortex behavior London to address the capacity and wake and to use this knowledge in alleviating airport vortices issue. This paper provides a brief capacity limitations caused by overly restrictive overview of the highlights of the oral wake turbulence separation standards. presentations. An international conference on Capacity and Wake Vortices was held September 12-14, 1 Introduction 2001, at the Imperial College of Science, Technology, and Medicine in London, UK. As the aviation community recovers from the The conference brought together researchers, events of September 11, 2001, airport capacity technologists, and the aviation community to limits will once more become a critical factor address the impact of aircraft wake vortices on affecting the growth and efficiency of air aviation system capacity. This paper will transportation. Many factors influence capacity summarize the highlights of the presentations -- climatology, runway configurations, traffic (there were no written papers) and comment on mix, etc. Ultimately, either the number of the progress of key topics since the conference. runways must be increased or the spacing Abstracts of the presentations can be found in 791.1 J.N. Hallock, C. Tung and S. Sampath the Wake Vortex Bibliography at locations. The eddy dissipation level in the http://www.volpe.dot.gov/wv. atmospheric turbulent boundary layer is a more stable quantity than the wind direction. He 2 Conference Presentations recommended that a warning of wake vortex circulation intensity above background should The subjects addressed at the conference be incorporated in the FAA Integrated included descriptions of the capacity problem Terminal Weather System. and strategies for the congested airports (3 Stefan Wolf (German Air Line Pilots sessions), recent investigations of vortices from Association) addressed issues of capacity vs. fixed-wing aircraft (2 sessions) and rotorcraft safety from a pilot’s view. Wake vortices are (3 sessions), progress in remote sensing of invisible to the pilot and a cause of uncertainty. wake vortices (1 session), modeling of vortex He wants to stay above and land beyond them. behavior (3 sessions), and consideration of He has to plan ahead and anticipate the wake possible methods for controlling vortex vortex hazard. He also needs to analyze the behavior (1 session). situation based upon his experience. Pilot input is required for scientific research, air traffic 2.1 Capacity and Strategies management providers, and aircraft manufacturers. In 1998, the International George Donohue (George Mason University) Federation of Air Line Pilots Associations opened the presentations with a discussion of issued a policy statement that included: the effect of wake-caused aircraft separation on • A general commitment to serious efforts air transportation capacity. The current allowing a safe reduction of the separation system seems overly conservative; a standard wake turbulence separation 15% increase in capacity could be achieved minima; without danger to safety. The current state-of- • Support for the results of international art sensors and vortex prediction and warning research activities contributing to the algorithms should be incorporated into Federal development of a wake vortex Aviation Administration (FAA) weather and air warning/avoidance system; traffic management decision support system • Need for airborne wake vortex detection software. However, accurate predictions of systems; and wake vortex locations and decay rates remain a • Need for ground-based wake vortex difficult problem, since the runway wind advisory and warning systems. direction variability is intrinsic to the Neil May (National Air Traffic Services randomness of the atmospheric turbulent Limited) reported a case study of runway boundary layer. It is a challenge to predict the capacity constraints at Heathrow Airport. The runway wind direction accurately out to 30 major constraints are: (1) in-bound and out- minutes – the time required to begin the bound traffic flow, (2) pilot performance (time spacing of arrival aircraft, which is to land and move out to a taxiway), (3) Air approximately 200 miles from the airport. Traffic Control procedures, (4) runway Based on theoretical calculations and the field configurations, (5) weather conditions, (6) results observed in the National Aeronautics airport layout, and (7) environment (12:00 to and Space Administration (NASA) Dallas-Fort 6:00 AM, no operations). Increasing the Worth experiments, the wake vortex decay capacity and reducing time delay requires: (1) rates can be predicted better than wake vortex smoothing the demand of in/out-bound traffic 791.2 CAPACITY AND WAKE VORTICES flow, (2) pilot education, (3) better controller ensures the aircraft’s flight corridor will be operational procedures, (4) providing clear of wake turbulence. infrastructures to reduce both pilots and air John Leverton (American Helicopter traffic controllers’ workload, and (5) Society International) examined the use of implementing a wake vortex separation vertical flight to improve airport capacity by distance change. using civil tilt rotor/helicopter to operate in the George Greene (FAA) presented the FAA’s unused airspace on the side of the airport. research strategy to enhance air traffic system Although the use of rotorcraft seems to be a capacity. FAA’s wake turbulence research real solution to reduce airport/airspace program (2001 to 2010) has been influenced by congestion, other factors like the cost, noise, the National Airspace System (NAS) passenger appeal, icing clearance, and wake Operational Evolution Plan need for vortex interaction need to be addressed. The assessment, the NASA near/long term research initial cost of the rotorcraft is high compared to program, the introduction of new large aircraft, the fixed-wing aircraft, but it can be and the international wake vortex research compensated by the slot value. The noise program. Special topics include near term generated by blade/vortex interaction is a major research on closely spaced parallel runways for issue to get community acceptance. Current San Francisco International Airport, research has made great progress in noise introduction of the simultaneous offset reduction. FAA uses 700 feet (ICAO uses 820 instrument approach (SOIA), evolution of feet) for runway separation between rotorcraft NASA’s Aircraft Vortex Spacing System and fixed wing aircraft to avoid wake vortex (AVOSS) technology for operational use, wake interaction. More research is needed to better safety simulation, and international define the separation distance. He estimated cooperation. that the use of rotorcraft may free up to 20% of Jens Konopka (German Air Navigation the slots. Services) gave an overview on the concept of David Rutishauser (NASA Langley the Wake Vortex Warning System (WVWS) Research Center) presented an overview of used at Frankfurt/Main Airport on runways 25L AVOSS, as demonstrated at the Dallas/Ft. and 25R (separated by 518 meters). The Worth (DFW) Airport in July 2000. AVOSS is measurement of the prevailing meteorological to determine the spacing required to prevent conditions and subsequent forecast of wake wake vortex encounters based on the ambient vortices motion between the two glide slopes weather conditions. The vortices from 61% of are accomplished. A wind/temperature radar the 2301 landings at DFW exited the corridor (1.3 GHz) provides the necessary data to in less than 50 seconds. Only 8% led to the extend the forecast along the entire final situation where the vortex predictor approach path of the two glide slopes. An underestimated the time for the vortices to exit alternative approach is presently in field trials the corridor (the vortices can translate outside based on the concept of High Approach the corridor, descend below it, or decay to less Landing System/Dual Threshold Operation than 90 m2/sec). Development of a research (HALS/DTOP) Project. The system ensures effort leading to a Wake Vortex Advisory that aircraft approaching runway 25L use a new System with limited capability (i.e., operate threshold displaced by 1500 meters (denoted only in certain weather conditions) is 26L) and thereby always stay 80 meters above underway. a leading aircraft on 25R. This 80-meter shift 791.3 J.N. Hallock, C. Tung and S. Sampath Anton de Bruin (NLR) described a Favorable