The Federal Aviation Administration (FAA) and industry are moving towards a more flexible, user oriented air traffic control system. The question is: does this point to a natural evolution or revolution in the world of the air traffic controllers? The National Airspace System is by all accounts the safest in the world. How will we sustain this record of performance with increased flexibility and user involvement? How will controllers and pilots react to a new more dynamic paradigm? Is the current state of automation, modeling, and analysis what is needed to make Free Flight a reality? How will the FAA insure that all human factors questions are answered before implementation? How will we quantify the impact of unanswered questions and their influence on safety? These, and many more questions need to be answered to ensure that the benefits promised by Free Flight are realized by all parties. The National Air Traffic Controllers Association supports the new concept. Yet, we are seriously concerned about the actual implementation of Free Flight's various components.

Successful implementation of the free flight concept requires new technologies, associated procedures, and standards for the flightcrew, the air traffic service provider, and, where applicable, the dispatcher. This paper explores several cockpit technologies and procedures that enable free flight. These enabling technologies are integrated through an operational system concept known as situational awareness for safety (SAS). SAS was intended, from its onset in 1992, as a means to communicate effectively between pilots, controllers, and dispatchers a wide variety of pertinent information relevant to safety and efficiency of flight. SAS-related information deals with the aircraft's external operating environment as well as aircraft 'status' information. Both elements are critical to the pilot's decision-making process. Initial 'core' SAS applications include: sharing of satellite-based position-in-space and other data between nearby aircraft as well as the air traffic service provider; data-linked graphical and textual weather and airport capacity/delay information to the cockpit (i.e.,'weatherlink'); and onboard terrain data files from which to create '2D' terrain overlay and '3D' dynamic image displays. Both the '2D' and '3D' displays provide predictive controlled flight into terrain protection. There software applications, along with the necessary data links, will help make free flight a distinct technical possibility.

This paper describes an experimental broadcast data link system architecture to identify and validate requirements for a broadcast data link and associated applications. Three key broadcast applications, including: automatic dependent surveillance-broadcast, flight information services-broadcast, and traffic information service-broadcast, are being investigated. The experimental system comprises three prototype components. The components are the universal access transceiver, the airborne research prototype, and the ground broadcast server. Simplicity, affordability, and beneficial capabilities are the driving considerations for this work. The operational objectives are: to provide capabilities that are simple, affordable, and provide immediate benefit and utility to the aircraft operator; to enhance the user's ability to maintain separation from other aircraft; and to enable simplifications to the air traffic management process.

The Harris Gulf of Mexico Buoy Communications System (BCS) provides air-to- ground communications between pilots and controllers over the Gulf of Mexico Flight Information Region. The BCS is a key element in the Federal Aviation Administration's goal for increasing air traffic across the Gulf area, resulting in increased safety, decreased flight time, and lower fuel consumption. By utilizing a network of satellites and water buoy-based radio links to supplement on shore remote center air-to-ground radio sites, the BCS provides controllers with direct voice communications to pilots in the latitude ranges of 18,000-60,000 feet. The BCS is a weather-resistant satellite solution on a stabilized platform. The pedestal design allows the antenna dish to remain locked on the satellite even under the most severe weather conditions. This low-risk design with built-in redundancy utilizes proven, commercial off-the-shelf/non-developmental item hardware and monitor and control software.

Airport surface movement communications, navigation, surveillance and decision support automation are discussed within the context of a national airspace system architecture. Current efforts underway by the Federal Aviation Administration and collaboration with users and the international community are described. International goals for advanced surface movement are defined and transition for communication, navigation, and surveillance are presented.

The Federal Aviation Administration has established an integrated program to provide wind shear detection and warning at selected airports throughout the United States. The program consists of both ground and aircraft-based sensors, as well as the development of procedures and training aids for pilots and controllers. Selection of airport for ground-based systems was based on the current and projected operations tempo and on the frequency of thunderstorms, the principal cause of hazardous wind shear events. The FAA's procurement of ground-based systems is managed within a wind shear product line in the agency's integrated product team for surveillance and weather. Included in the product line are the terminal doppler weather radar, the low level wind shear alert system, and the airport surveillance radar-weather system processor. These three systems, coupled with new procedures and improved training, bring a truly integrated approach to solving a serious safety problem.

The AlliedSignal RDR-4B, a state-of-the-art digital airborne weather radar capable of forward-looking/predictive windshear detection, is presented. The weather phenomenon known as microbursts and windshears are overviewed. In reviewing the 'physics' of windshear, the need for a forward-looking sensor is established and the selection of digital radar as a means-to-the-end is justified. The RDR-4B system capabilities are then summarized, followed by a top-level breakdown of the radar and associated windshear detection processing. Key discussions include formation of Doppler frequency domain data, adaptive rejection of clutter spectra, and statistical characterization of retained weather/windshear spectra. An explanation of how these statistics come to indicate a windshear's existence and severity, in terms of hazard factors, follows. The paper concludes by documenting an actual windshear's detection prior-to-encounter and subsequent penetration by a RDR-4B equipped test aircraft.

Many clear air turbulence (CAT) encounters have been identified as having been caused by aircraft flying through discrete vortices such as those generated by Kelvin-Helmholtz instabilities. It is the purpose of this paper to demonstrate that if an aircraft's autopilot can be forewarned of an impending hazard, by means of atmospheric measurements ahead, it can control the aircraft in such a way as to reduce significantly the effect of the disturbance. There are several technologies currently available which can make atmospheric measurements ahead of an aircraft in flight, but for atmospheric phenomena which may be invisible to the naked eye (e.g. CAT), airborne lidar systems have shown the greatest potential. Results presented in this paper illustrate the potential advantages of feeding-forward such predictive measurements to an aircraft's control system in cruising flight when encountering severe turbulence induced by a vortex, in order to alleviate the effect of the disturbance. It is shown, by means of flight simulation, that active pitch control in vortex-induced turbulence encounter can significantly reduce the level of upset experienced by an aircraft. Flight simulations were performed which corroborated well with actual in-flight encounters, and illustrated the effectiveness of appropriate pitch control.

It has been apparent for more than a decade that the weather-forecast wind speed reaching flight crews in commercial aircraft differs by an average of +/- 15 knots from the wind speed actually experienced during the flight at cruise altitude. We recently analyzed wind-versus-altitude forecasts and found that the forecast altitude of maximum wind is also in error, by an average of +/- 4800 feet. In this era of increasing free-flight operations, we propose the use of airborne laser radar to measure winds above and below the aircraft in real time, so that a pilot can optimize the flight altitude with respect to prevailing winds. Analysis shows that such a lidar system would generate fuel savings of $LR100,000 to $LR200,000 per aircraft per year, especially for transoceanic routes. THis saving would pay for the instrument in one to two years.

The using of shift interferometry methods allowed to detect the existence of helical dislocations on the wave front of He-Ne laser beam propagating through the paths near the ground. Taking the dislocation structure into account gave the opportunity to estimate the intensity of the turbulent state of the channel. Two states of beam distortions are described. An attempt was made to connect the dislocation structure of a beam with the effect of 'turbulence intermittence'. Simultaneous measurements of aerosol density and IR radiation parameters were carried out and compared with He-Ne beam structure under different propagation conditions.

NASA, and its predecessor, the National Advisory Committee for Aeronautics, have been conducting aeronautics research since 1915, helping make US aviation the multi-billion dollar industry it is today. But NASA is not alone, and is strongly committed to a thriving partnership with the Federal Aviation Administration is support of US aviation. NASA's Aeronautics program traditionally concentrated on improving a vehicle's efficiency and performance. However, a vehicle's ultimate performance is dictated by its ability to operate within an integrated aviation system. This must reflect the constraints of standards and regulations that ensure safety and a clean and quiet environment. It must also recognize a user's ability to operate productively in an airspace system that accommodates the users' need for flexibility within the system's capacity. Aeronautics' programs span all elements of this integrated aviation system. This paper will focus on those efforts to ensure user flexibility and system capacity, and provide an overview of NASA airspace operations and flight systems technology and its diverse customer base of technology products. The research and technology that we apply to today's garden of planned improvements for avionics and air traffic must be husbanded in the context of an integrated aviation system. In that way the aviation community will be able to harvest the next century's low-hanging fruit in real technologies and procedures. The operational concept called free flight is the keystone.

A CW-coherent laser radar using a 20-watt CO₂ laser has been constructed and deployed for the measurement of wake-vortex turbulence. This effort is part of the NASA Terminal Area Productivity Program and has the goal of providing information to further the understanding of the motion and decay of wake vortices as influenced by the local atmospheric conditions. To meet this goal, vortex measurements are made with the lidar along with simultaneous measurements from a suite of meteorological sensors which include a 150 foot instrumented tower, a profiler/RASS, sodar and balloon soundings. The information collected also includes airline flight data and beacon data. The operation of the lidar during two field deployments at Memphis International Airport are described as well as examples of vortex motion and decay measurements in various atmospheric conditions.

The APALS system is a precision approach and landing system designed to enable low visibility landings at many more airports than now possible. Engineering development of the APALS system began October 1992 culminating in the pre- production Advanced Development Model (ADM) system currently undergoing flight testing. The paper focuses on the Cat III accuracy and integrity requirements defined by ICAO, Annex 10 and the required navigation performance (RNP) tunnel concept. The resulting ADM architecture developed to meet them is described. The primary measurement is made with the aircraft's weather radar and provides range and range rate information to the ADM necessary to update the precision navigation state vector. The system uses stored terrain map data as references for map matching with synthetic aperture radar with synthetic aperture radar maps. A description of the pre-production flight test program is included. Testing is being conducted at six different airports around the country demonstrating system performance in various environmental conditions (precipitation, heavy foliage, sparse terrain, over water and turbulence). ADM flight test results of 131 successful CAT II hand-flown approaches at ALbuquerque, NM and Richmond, VA are presented. Detailed statistical analysis of these results indicate that the APALS system meets the RNP for Cat III.

Solid-state coherent Doppler lidar systems are rapidly emerging as useful tools for boundary layer wind profiling. These Doppler lidars provide sufficient temporal,s spatial and velocity resolution to serve as an adjunct sensor, providing both real-time hazard detection as well as large-area wind state data for input to predictive models. THis paper briefly reviews recent results produced with a mobile flashlamp-pumped 2.09 microns coherent lidar sensor for windshear detection and measurement and wind turbulence estimation at the site of the new Hong Kong airport. Wind state predictions based on a fine-mesh mesoscale model are compared with the lidar results.

The 1995 report of the RTCA Board of Directors' Select Committee on Free Flight states that 'insufficient capacity, limited access, and excessive operating restrictions have escalated operating costs, increase delays, and decreased efficiency for all users' of the national airspace system. The Air Transport Association estimates the annual loss to be 3.5 billion dollars. The goal of the user preferred routing research is to develop integrated airborne and ground technologies that enable the highest possible level of unconstrained, user-preferred routing in enroute airspace.

Current operational airport surface surveillance systems do not positively identify aircraft as unique targets. Air Traffic Controllers are instead presented with a primary radar picture showing all traffic on the airport movement area. The FAA is evaluating different types of systems that will add the aircraft's call-sign or flight number to the radar image thereby allowing controllers to positively identify individual aircraft at all times. This paper describes the development, implementation, and testing of the Airport Surface Target Identification System, and presents results of initial trials conducted at Atlanta Hartsfield International Airport.