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The FAA Terminal Doppler Weather (TDWR) Program
February 3, 1989
Conference Paper
Published in:
Proc. Third Int. Conf. on the Aviation Weather Systems, 30 January - 3 February 1989, pp. 414-419.
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Summary
The Federal Aviation Administration (FAA) initiated the Terminal Doppler Weather Radar (TDWR) program in the mid-1980s in response to overwhelming scientific evidence that low-altitude wind shear had caused a number of major air-carrier accidents. The program is designed to develop a reliable automated system for detecting low-altitude wind shear in the terminal area and providing warnings that will help pilots successfully avoid it on approach and departure. Wind shear has caused more U.S. air-carrier fatalities than any other weather hazard. A 1983 National Research Council (NRC) study (National Research Council, 1983) identified low-altitude wind shear as the cause of 27 aircraft accidents and incidents between 1964 and 1982. A total of 488 people died in seven of these accidents, 112 of them in the 1975 crash of Eastern Flight 66 at New York and 153 in the crash of Pan American Flight 759 at New Orleans in 1982. Since the NRC study was completed, the National Transportation Safety Board (NTSB) has investigated at least three more wind-shear incidents. One of these, the crash of Delta Flight 191 at Dallas/Fort Worth on August 2, 1985, took another 137 lives. Wind shear is not a serious hazard for aircraft enroute between airports at normal cruising altitudes, but low-level wind shear in the terminal area can be deadly for an aircraft on approach or departure. The most hazardous form of wind shear is the microburst, an outflow of air from a small-scale but powerful downward gush of cold, heavy air that can occur beneath a thunderstorm or rain shower or even in rain-free air under a harmless-looking cumulus cloud. As this downdraft reaches the earth's surface, it spreads out horizontally, like a stream of water sprayed straight down on a concrete driveway from a garden hose. An aircraft that flies through a microburst at low altitude first encounters a strong headwind, then a downdraft, and finally a tailwind that produces a sharp reduction in airspeed and a sudden loss of lift. This deadly sequence of events caused the fatal crash at Dallas/Fort Worth in 1985, as well as a number of other serious air-carrier accidents. Wind shear can also be associated with gust fronts, warm and cold fronts, and strong winds near the ground. It is important for pilots to be trained in recovery techniques to use if they are caught in wind shear. But a sudden windspeed change of at least 40 to 50 knots, which is not uncommon in microbursts, presents a serious hazard to jet airliners, and some microbursts simply are non-survivable. The only sure way to survive wind shear in the terminal area is to avoid it. However, flight crews do not have adequate information available today to predict or detect wind shear. The primary goal of the IDWR program is to provide pilots with an objective, quantitative assessment of the wind-shear hazard. The TDWR system also will improve operational efficiency and reduce delays in the terminal area by providing air traffic control supervisors with timely warnings of impending wind shifts resulting from gust fronts.
Summary
The Federal Aviation Administration (FAA) initiated the Terminal Doppler Weather Radar (TDWR) program in the mid-1980s in response to overwhelming scientific evidence that low-altitude wind shear had caused a number of major air-carrier accidents. The program is designed to develop a reliable automated system for detecting low-altitude wind shear in...
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Applying artificial intelligence techniques to air traffic control automation
January 1, 1989
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 537-554.
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We have developed a computer program that automates rudimentary air traffic control (ATC) planning and decision-making functions. The ability to plan, make decisions, and act on them makes this experimental program qualitatively different from the more clerical ATC software currently in use. Encouraging results were obtained from tests involving simple scenarios used to train air traffic controllers.
Summary
We have developed a computer program that automates rudimentary air traffic control (ATC) planning and decision-making functions. The ability to plan, make decisions, and act on them makes this experimental program qualitatively different from the more clerical ATC software currently in use. Encouraging results were obtained from tests involving simple...
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Experimental examination of the benefits of improved terminal air traffic control planning
January 1, 1989
Journal Article
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Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 527-536.
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Airport capacity can be improved significantly-by precisely controlling the sequence and timing of traffic flow-even when airspace usage and procedures remain fixed. In a preliminary experiment, a plan for such sequencing and timing was applied in a simulation to a 70-min traffic sample observed at Boston's Logan Airport, and the result was a 13% increase in terminal throughput. A total of 2.2 aircraft flight hours were saved. Delays imposed upon arriving traffic in the simulation were much more equitably distributed than in the actual traffic sample. An even greater improvement may be possible if controllers are able to space aircraft more precisely on final approach than was achieved in the simulation. If the plan had been followed precisely, the throughput increase would have been 23%.
Summary
Airport capacity can be improved significantly-by precisely controlling the sequence and timing of traffic flow-even when airspace usage and procedures remain fixed. In a preliminary experiment, a plan for such sequencing and timing was applied in a simulation to a 70-min traffic sample observed at Boston's Logan Airport, and the...
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Parallel runway monitor
January 1, 1989
Journal Article
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Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 411-436.
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The availability of simultaneous independent approaches to parallel runways significantly enhances airport capacity. Current FAA procedures permit independent approaches in instrument meteorological conditions (IMC) when the parallel runways are spaced at least 4,300 ft apart. Arriving aircraft must be dependently sequenced at airports that have parallel runways separated by less than 4,300 ft, a procedure that reduces the arrival rate by as much as 250h. The need for greater airport capacity has led to intense interest in new technologies that can support independent parallel IMC approaches to runways spaced as close as 3,000 ft. This interest resulted in several FAA initiatives, including a Lincoln Laboratory program to evaluate the applicability of Mode-S secondary surveillance radars for monitoring parallel runway approaches. This paper describes the development and field activities of this program.
Summary
The availability of simultaneous independent approaches to parallel runways significantly enhances airport capacity. Current FAA procedures permit independent approaches in instrument meteorological conditions (IMC) when the parallel runways are spaced at least 4,300 ft apart. Arriving aircraft must be dependently sequenced at airports that have parallel runways separated by less...
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Propagation of mode S beacon signals on the airport surface
January 1, 1989
Journal Article
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Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 397-410.
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Many airports across the United States will soon be equipped with Mode S, a next generation beacon (or secondary) radar system. One feature of Mode S is that it provides a data link between airborne aircraft and air traffic controllers. If Mode S could be used to communicate with aircraft on the airport surface, the radar system would improve airport safety and efficiency on runways and taxiways. The airport surface, however, is a hostile propagation environment. This article outlines a candidate design for the propagation of Mode-S beacon signals on the airport surface. Data that support the feasibility of Mode S for surveilling runways and taxiways are presented.
Summary
Many airports across the United States will soon be equipped with Mode S, a next generation beacon (or secondary) radar system. One feature of Mode S is that it provides a data link between airborne aircraft and air traffic controllers. If Mode S could be used to communicate with aircraft...
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TCAS: a system for preventing midair collisions
January 1, 1989
Journal Article
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Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 437-458.
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To reduce the possibility of midair collisions, the Federal Aviation Administration has developed the Traffic Alert and Collision Avoidance System, or TCAS. This airborne system senses the presence of nearby aircraft by interrogating the transponders carried by these aircraft. When TCAS senses that a nearby aircraft is a possible collision threat, TCAS issues a traffic advisory to the pilot, indicating the presence and location of the other aircraft. If the encounter becomes hazardous, TCAS issues a maneuver advisory.
Summary
To reduce the possibility of midair collisions, the Federal Aviation Administration has developed the Traffic Alert and Collision Avoidance System, or TCAS. This airborne system senses the presence of nearby aircraft by interrogating the transponders carried by these aircraft. When TCAS senses that a nearby aircraft is a possible collision...
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The mode S beacon radar system
January 1, 1989
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 2, No. 3, Fall 1989, pp. 345-362.
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Air traffic controllers rely on primary and secondary radars to locate and identify aircraft. Secondary, or beacon, radars require aircraft to carry devices called transponders that enhance surveillance echoes and provide data links. Airports currently use a secondary-radar system known as the Air Traffic Control Radar Beacon System (ATCRBS). However, ATCRBS has limitations in dense-traffic conditions, and the system's air-to-ground data link is limited. In response to these shortcomings, Lincoln Laboratory has developed the Mode Select Beacon System (referred to as Mode S), a next-generation system that extensive laboratory and field testing has validated. In addition to significant surveillance improvements, Mode S provides the general-purpose ground-air-ground data link necessary to support the future automation of air traffic control (ATC). The Federal Aviation Administration (FAA) is currently installing the system with initial operation scheduled for 1991.
Summary
Air traffic controllers rely on primary and secondary radars to locate and identify aircraft. Secondary, or beacon, radars require aircraft to carry devices called transponders that enhance surveillance echoes and provide data links. Airports currently use a secondary-radar system known as the Air Traffic Control Radar Beacon System (ATCRBS). However...
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Airport surface traffic automation study
May 9, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-156
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This report documents a study of requirements for an Airport Surface Traffic Automation (ASTA) system. The objective was to determine the necessary functions, establish the cost and benefits, and outline a modular system design. The highest priority function identified was an improved surface surveillance and communication system. The greatest potential for safety benefits is provided by automatic conflict alert and collision warning for pilots and controllers to prevent runway incursion accidents. Strategic and tactical planning assistance to maximize runway utilization can improve controller productivity while keeping them responsible for final decisions. The report contains a modular design for ASTA and includes specifications for a man-in-the-loop simulation of the system.
Summary
This report documents a study of requirements for an Airport Surface Traffic Automation (ASTA) system. The objective was to determine the necessary functions, establish the cost and benefits, and outline a modular system design. The highest priority function identified was an improved surface surveillance and communication system. The greatest potential...
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TDWR PRF selection criteria
March 15, 1988
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-147
Summary
The Terminal Doppler Weather Radar (TDWR) system shall provide high quality Doppler radar data on weather phenomena near high traffic airports. These data shall be used in real time by automated TDWR algorithms to detect weather situations which may be hazardous to the safe operation of aircraft within the vicinity of the airport. One of the major factors which could cause the degradation of the quality of these TDWR data is obscuration by 'distant' storm cells. This obscuration is caused by storms located beyond the range interval being sampled by the radar, yet whose radar echo ambiguously folds within the range interval of interest. These range aliased echoes could trigger false detections by the algorithms, and/or cause actual hazardous situations near the airport to remain undetected. By carefully selecting the pulse repetition frequency (PRF) of the radar, range obscuration from distant storms can be minimized over specified airport regions. This document describes techniques for predicting the obscuration as a function of PRF, and details the criteria which shall be used by the TDWR system to automatically and adaptively select an optimal PRF in order to minimize these obscuration effects. Weather radar, Radar range obscuration, TDWR, Radar range aliasing, Radar pulse, Repetition Frequency (PRF).
Summary
The Terminal Doppler Weather Radar (TDWR) system shall provide high quality Doppler radar data on weather phenomena near high traffic airports. These data shall be used in real time by automated TDWR algorithms to detect weather situations which may be hazardous to the safe operation of aircraft within the vicinity...
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Surveillance processing in the Mode S sensor
October 21, 1987
Conference Paper
Published in:
Radar-87, IEE Int. Conf., London, U.K., 19-21 October 1987, pp. 189-194.
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The principal function of the Mode S sensor (1), an evolutionary upgrade to the current ATCRBS (Air Traffic Control Radar Beacon System) sensor, is the output of one reportper aircraft per antenna scan. This report contains the current aircraft position (range and azimuth), the identity code of its transponder, and the altitude code as supplied by its encoding altimeter. This information is derived from the aircraft transponder replies received at the sensor in response to interrogations transmitted by the sensor. For aircraft equipped with Mode S transponders, a single scheduled interrogation, directed only to that aircraft, elicits a single coding-protected reply containing both identity code and altitude code. For aircraft equipped with ATCRSS transponders, a sequence of interrogations alternately eliclt replies containing un-protected identity code or altitude code from all aircraft in the antenna mainbeam. From this description, it is clear that a Mode S aircraft report can be constructed directly fron the single reply. Surveillance processing, defined as functions that perform scan-to-scan correlation and tracking, are required in general only to predict the next scan position of the aircraft. This information is needed for the proper scheduling of the next interrogation. ATCRBS reports constructed from the aircraft replies, on the other hand, can have a number of deficiencies. The more common such problems are: 1. Either the identity code or altitude code or both can have bits declared either in error or with low confidence by the reply processor due to garbling of overlapping replies. 2. False alarm reports not corresponding to aircraft can be generated from fruit replies (responses to other sensors' interrogations) or reflection replies. 3. Multiple reports for an aircraft can be generited due to incorrect correlation of replies caused by errors in range, azimutn, or code determination. Surveillance processing for ATCRBS aircraft is tasked with correcting these problems prior to report output to the controllers or other users. It does this by correlating raw target reports with, existing track files, and using the information in these files derived from prior scan reports to correct, complete, or reject erroneous reports. This paper presents the major algorithms contained within the Mode S sensor ATCRBS surveillance processing function. It then presents experimental results that demonstrate their effectiveness. Full details of surveillance processing can be obtained by reference to (2) or [3).
Summary
The principal function of the Mode S sensor (1), an evolutionary upgrade to the current ATCRBS (Air Traffic Control Radar Beacon System) sensor, is the output of one reportper aircraft per antenna scan. This report contains the current aircraft position (range and azimuth), the identity code of its transponder, and...
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