tcas - traffic alert and collision avoidance system

7/27/2019 TCAS - Traffic Alert and Collision Avoidance System

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TCAS: Traffic Alert and Collision Avoidance System

Traffic Alert and Collision Avoidance SystemThe Traffic Alert and Collision Avoidance System, or TCAS, is an instrumentintegrated into other systems in an aircraft cockpit. It consists of hardware and software

that together provide a set of electronic eyes so the pilot can "see" the traffic situation inthe vicinity of the aircraft. Part of the TCAS capability is a display showing the pilot therelative positions and velocities of aircraft up to 40 miles away. The instrument soundsan alarm when it determines that another aircraft will pass too closely to the subjectaircraft. TCAS provides a backup to the air traffic control systems regular separation

processes.The MITRE Corporation conducted early research into collision avoidance technologiesunder the sponsorship of the Federal Aviation Administration (FAA). TCAS is a directdescendant of those invented at MITRE and elsewhere. To learn more about TCAS, andthe people who invented it, read further, or click on the following sections:

Background Historical Perspective A Collision Avoidance System is Born Taking to the Skies: The Congressional Mandate Evolving to Meet Safety Needs

Background

Since the early 1960s, MITRE's Center for Advanced Aviation System Development(CAASD) has provided the FAA with Air Traffic Control (ATC) system engineeringsupport. As part of this longstanding partnership, CAASD helped the FAA implement a

collision avoidance system for aircraft. The resulting Traffic Alert and CollisionAvoidance System, or TCAS, has become a standard for safety in the United States andabroad. Its value is clear: no airline mid-air collisions have occurred in the United Statessince 1990, when the airlines began equipping their planes with TCAS.From its inception, TCAS has dramatically improved pilots' chances of successfullyaverting the threat of a mid-air collision. Pilots have come to rely on TCAS to give themthe crucial data to avoid collisions. As their last line of defense, TCAS gives pilots theedge needed to ensure that their crew and passengers have the safest flight possible.The project benefited from the cooperative efforts of the FAA, airlines, and severalother companies. CAASD designed and developed the collision avoidance logic at theheart of the system. The Massachusetts Institute of Technology's Lincoln Laboratory

developed air-to-air surveillance. The FAA Technical Center and a team of contractors,including The Analytical Sciences Corporation, Coleman Research Corporation, andRannoch Corporation, were responsible for software verification and validation. TheFAA Technical Center and ARINC Research handled operational evaluations.

Historical Perspective

On June 30, 1956, two planes collided over the Grand Canyon. In the wake of this andother such airborne disasters, the industry realized they needed a system that could help

prevent similar incidents. Companies soon began designing collision avoidancesystems, but two problems hampered their efforts. First, adoption of the proposed

systems would require the airlines to equip their fleets with expensive new hardware.


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Second, there was still a lot of development left to do before an adequate system wouldbe ready.

In 1974, MITRE proposed an alternative. Using the transponders already installed in

many aircraft for communication with the FAA's ground-based Air Traffic ControlRadar Beacon System (ATCRBS), developers took advantage of existing technologiesto significantly hasten the design and implementation process. The Beacon-BasedCollision Avoidance System (BCAS) was the predecessor of today's TCAS. Thissystem sent interrogation signals to nearby aircraft similar to the FAA's radar system.The transponders then sent back response signals. The system interpreted these signalsto determine the location, speed, and course of each plane and used the data to avoid a

potential collision.BCAS test results were promising. On the ground, MITRE equipped a trailer to receivetransponder signals as if it were an aircraft. BCAS lived up to expectations, promptingthe FAA Technical Center to test the system on one of its aircraft. On the basis of thesetwo tests, the FAA moved forward with further development of BCAS.

A Collision Avoidance System Is Born

In 1981, the FAA chose to pursue the onboard design approach used in BCAS ratherthan a ground-based collision avoidance system which was also under consideration. Atthat point, BCAS was renamed TCAS.There are two different versions of TCAS, for use on different classes of aircraft. Thefirst, TCAS I, indicates the bearing and relative altitude of all aircraft within a selectedrange (generally 10 to 20 miles). With color-coded symbols, the display indicates which

aircraft pose potential threats. This constitutes the Traffic Advisory (TA) portion of thesystem. When pilots receive a TA, they must visually identify the intruding aircraft andmay alter their plane's altitude by up to 300 feet. TCAS I does not offer solutions, butdoes supply pilots with important data so that they can determine the best course ofaction. An illustration of TCAS range and altitude criteria shows the horizontal andvertical distances to monitor traffic and issue advisories to maintain safe separation ofaircraft.In addition to a traffic display, the more comprehensive TCAS II also provides pilotswith resolution advisories (RAs) when needed. The system determines the course ofeach aircraft; climbing, descending, or flying straight and level. TCAS II then issues anRA advising the pilots to execute an evasive maneuver necessary to avoid the other

aircraft, such as "Climb" or "Descend." If both planes are equipped with TCAS II, thenthe two computers offer deconflicting RAs. In other words, the pilots do not receive


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advisories to make maneuvers that would effectively cancel each other out, resulting ina continued threat.

TCAS queries other aircraft, receives information, displays traffic,and reacts by warning pilots when there is a potential threat.

MITRE's key contribution to the development of TCAS was its work on the collisionavoidance logic for TCAS II. The software uses the collected data on the flight patternsof other aircraft and determines if there is a potential collision threat. The system doesn't

just show the other planes on a display like a radar screen, but offers warnings and

solutions in the form of traffic advisories (TAs) and resolution advisories (RAs).As CAASD's Dr. Andrew Zeitlin points out, "Because of the pilots' normal workload,we don't expect them to spend all of their time looking at the screen. It's there whenneeded, but more important, it speaks up and advises them as they need to make amaneuver to avoid a collision."Aside from the logic design, much of MITRE's work on TCAS involved creating andrunning computer simulations to test the system. "Because it's expensive to fly testencounters," says Dr. Zeitlin, "we have developed some very powerful tools where wecan generate millions of encounters on the computer and evaluate the logicexhaustively. We can also play back radar data from ordinary traffic and get a feel forhow the system works and how much disruption you get day to day or at different

locations with ordinary traffic." On occasion, MITRE has also assisted the FAA andother organizations in evaluating special encounters. "For example, if somebody has anear-miss and they want to know what TCAS's role was or what would TCAS havedone in the encounter, we can simulate the encounter and give advice," says Zeitlin.Back to Top Taking to the Skies: The Congressional MandateOn August 31, 1986, while TCAS was still in development, a collision occurred overCerritos, California, involving an Aeromexico DC-9 and a small Piper aircraft carryinga family of three. The DC-9 was descending toward Los Angeles International Airportin clear skies, flying at 6,500 feet. The Piper hit the DC-9's tail, causing both aircraft to

plummet from the sky.The accident resulted in the deaths of all 67 people aboard the two planes, as well as 15

people on the ground. In the aftermath of this accident, Congress passed a law requiring


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the FAA to mandate the use of TCAS. By 1993, all carrier aircraft operating within U.S.airspace with more than 30 passenger seats were equipped with TCAS II. Aircraft with10 to 30 seats were required to employ TCAS I.

Evolving to Meet Safety Needs

Although the airlines were using the more advanced version 6.01 of the TCAS logic,some improvements still needed to be made. The system was issuing RAs in somesituations, such as final approach, when traffic may be closer but is safely under control.Many pilots saw these RAs as a nuisance. The system was basically too sensitive, withunnecessary TAs and RAs even being triggered by transponders on bridges and ships.According to Dr. Zeitlin, "There was a growing tendency among pilots to ignore theadvisory, even when they didn't necessarily have full knowledge of the situation.Everyone was concerned that one day they would ignore one that was necessary."In 1992, CAASD developed logic version 6.04 to alleviate these problems. DeltaAirlines, the first carrier to voluntarily use the new logic, reported an 80 percent

reduction in RAs. The following year, CAASD developed an additional improvementto the logic, version 6.04A. Airlines began equipping their fleets with this version in1994.

The Final Generation

In 1997, CAASD finished work on one final major change to the TCAS logic, version7. It was approved by the RTCA standards committee and the FAA, and is the versionthat will be installed on all new aircraft. It has also been adopted by the InternationalCivil Aviation Organization (ICAO) as the international standard. Initially, version 7will be installed on aircraft serving European and some other countries. Americancarriers who fly to these countries will have to upgrade from 6.04A to 7 on theirinternational planes, and can voluntarily upgrade the equipment already on their U.S.fleets.

According to program manager David Lubkowski, who led CAASD's TCAS softwaredevelopment group, the version 7 logic should yield at least a 20 percent reduction inRAs over the previous version. "We also ran simulations using radar data from Europe,where they encounter more high-altitude en route conflicts," he said. "The new 7.0software resulted in a 40 percent reduction in unnecessary RAs." The new logic alsosignificantly improves TCAS performance in several other important areas.CAASD personnel have conducted safety studies to evaluate the performance of each

successive version of the TCAS logic. In a 1997 report on version 7, CAASD's Dr.Michael McLaughlin examined the reduced risk of collision in aircraft equipped with


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TCAS II versus the risk in aircraft without TCAS. Based on the likelihood of incursionsinto a protected zone around aircraft with a radius of 500 feet and a height of 200 feet --defined as Critical Near Mid-Air Collisions (NMACs) -- McLaughlin concluded that"TCAS should reduce NMAC probability by at least 90 to 98 percent," depending onwhether one or both aircraft in an encounter are equipped with TCAS.

Though NMACs, especially those involving commercial, passenger aircraft are alreadyextremely rare, McLaughlin notes that "TCAS is intended to reduce their probabilityeven further."Although the FAA has said that version 7 will be the final logic for TCAS, CAASDcontinues to work on many different air traffic control projects, and will undoubtedly

play a role in the development of any future collision avoidance systems.


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Alarma del trfico y sistema de la evitacin de la colisinEl sistema de la evitacin de la alarma y de la colisin del trfico, o TCAS, es uninstrumento integrado en otros sistemas en una carlinga de avin. Consiste en elhardware y el software que juntos proporcionan un sistema de ojos electrnicos as quela lata del piloto "ve" la situacin del trfico en la vecindad del avin. La parte de la

capacidad de TCAS es una exhibicin que demuestra al piloto las posiciones delpariente y las velocidades del avin hasta 40 millas lejos. El instrumento suena unalarmar cuando se determina que otro avin pasar demasiado de cerca al avin sujeto.TCAS proporciona una reserva a los procesos regulares de la separacin del sistema decontrol del trfico areo.El MITRE Corporation condujo la investigacin temprana en tecnologas de la evitacinde la colisin bajo patrocinio de la administracin federal de la aviacin (FAA). TCASes un descendiente directo de sos inventados en el INGLETE y a otra parte. Paraaprender ms sobre TCAS, y a la gente que lo invent, lee ms lejos, o chascaencendido las secciones siguientes:

Fondo Perspectiva Histrica

Se lleva un sistema de la evitacin de la colisin

El llevar los cielos: El Mandato Del congreso

Desarrollo para satisfacer necesidades de seguridad

La Generacin Final

Fondo

Desde los aos 60 tempranos, el centro del inglete para el desarrollo avanzado delsistema de la aviacin (CAASD) ha provisto del FAA la ayuda de la ingeniera desistema del control del trfico areo (ATC). Como parte de esta sociedad de muchosaos, CAASD ayud al instrumento de FAA un sistema de la evitacin de la colisin

para el avin. El sistema de la evitacin de la alarma y de la colisin del trfico queresultaba, o TCAS, se ha convertido en un estndar para la seguridad en los EstadosUnidos y al exterior. Su valor est claro: ningunas colisiones del mediados de-aire de lalnea area han ocurrido en los Estados Unidos desde 1990, cuando las lneas areascomenzaron a equipar sus planos de TCAS.De su inicio, TCAS ha mejorado dramticamente las ocasiones de los pilotos con xitode evitar la amenaza de una colisin del mediados de-aire. Los pilotos han venidoconfiar en TCAS para darle los datos cruciales para evitar colisiones. Como su lnea dedefensa pasada, TCAS da a pilotos el borde necesitado para asegurarse de que su equipo

y pasajeros tengan el vuelo ms seguro posible.El proyecto benefici de los esfuerzos cooperativos del FAA, de lneas areas, y devarias otras compaas. CAASD dise y desarroll la lgica de la evitacin de lacolisin en el corazn del sistema. El instituto de Massachusetts del laboratorio deLincoln de la tecnologa desarroll vigilancia air-to-air. El centro tcnico de FAA y unequipo de contratistas, incluyendo los Analytical Sciences Corporation, ColemanResearch Corporation, y Rannoch Corporation, eran responsables de la verificacin y dela validacin del software. El centro tcnico de FAA y la investigacin de ARINCmanejaron evaluaciones operacionales.Perspectiva HistricaDe junio el 30 de 1956, dos planos chocaron sobre la barranca magnfica. En la estela de

esto y de otros tales desastres aerotransportados, la industria realiz que necesitaron unsistema que podra ayudar a prevenir incidentes similares. Las compaas pronto


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comenzaron a disear sistemas de la evitacin de la colisin, pero dos problemasobstaculizaron sus esfuerzos. Primero, la adopcin de los sistemas propuestos requeriralas lneas areas equipa sus flotas de hardware nuevo costoso. En segundo lugar, habamuchos inmviles de desarrollo a la izquierda de hacer antes de que un sistemaadecuado fuera listo.

En 1974, el INGLETE propuso un alternativa. Usando los transpondores instalados yaen muchos el avin para la comunicacin con el sistema de faro de radar de control detrfico areo terrestre del FAA (ATCRBS), los reveladores se aprovech de tecnologasexistentes para acelerar perceptiblemente el proceso del diseo y de la puesta en

prctica. El sistema Faro-Basado de la evitacin de la colisin (BCAS) era el precursorde TCAS de hoy. Este sistema envi seales de la interrogacin al avin prximosimilar al sistema del radar del FAA. Los transpondores entonces enviaron detrsseales de respuesta. El sistema interpret estas seales de determinar la localizacin, lavelocidad, y el curso de cada plano y utiliz los datos para evitar una colisin potencial.Los resultados de la prueba de BCAS eran prometedores. En la tierra, el INGLETEequip un acoplado para recibir seales del transpondor como si fuera un avin. BCASvivi hasta las expectativas, incitando el centro tcnico de FAA para probar el sistemaen uno de su avin. En base de estas dos pruebas, el FAA se movi adelante con eldesarrollo adicional de BCAS.

Se lleva Un Sistema De la Evitacin De la Colisin

En 1981, el FAA eligi perseguir el onboard el acercamiento del diseo usado en BCASms bien que sistema terrestre de la evitacin de la colisin que estaba tambin bajo

consideracin. En ese punto, BCAS fue retitulado TCAS.Hay dos diversas versiones de TCAS, para el uso en diversas clases del avin. Elprimer, TCAS I, indica el cojinete y la altitud relativa de todo el avin dentro de unagama seleccionada (generalmente 10 a 20 millas). Con smbolos color-coded, laexhibicin indica qu amenazas del potencial de la actitud del avin. Esto constituye la

porcin consultiva del trfico (TA) del sistema. Cuando los pilotos reciben TA, debenidentificar visualmente el avin de imposicin y pueden alterar la altitud de su plano porhasta 300 pies. TCAS I no ofrece soluciones, sino provee a pilotos de datos importantesde modo que puedan determinar la mejor lnea de conducta. Una ilustracin de loscriterios de la gama y de la altitud de TCAS demuestra las distancias horizontales yverticales a los advisories del trfico y de la edicin del monitor para mantener la

separacin segura del avin.


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Adems de una exhibicin del trfico, el TCAS ms comprensivo II tambin provee depilotos los advisories de la resolucin (rA) cuando est necesitado. El sistema determinael curso de cada avin; el subir, el descender, o el volar derecho y llano. TCAS IIentonces publica un RA que aconseja a los pilotos ejecutar una maniobra evasivanecesaria para evitar el otro avin, tal como "subida" o "descienda." Si ambos planos se

equipan de TCAS II, despus las dos computadoras ofrecen el rA deconflicting. Es decirlos pilotos no reciben advisories para hacer las maniobras fuera de las cuales secancelara con eficacia, dando por resultado una amenaza continuada.

TCAS pregunta el otro avin, recibe la informacin, exhibe trfico,

y reacciona por los pilotos de la advertencia cuando hay una amenaza potencial.

La contribucin dominante del inglete al desarrollo de TCAS era su trabajo sobre lalgica de la evitacin de la colisin para TCAS II. El software utiliza los datosrecogidos sobre los patrones del vuelo del otro avin y se determina si hay una amenaza

potencial de la colisin. El sistema apenas no demuestra los otros planos en unaexhibicin como una pantalla de radar, sino las advertencias de las ofertas y lassoluciones en la forma de los advisories del trfico (TA) y de advisories de la resolucin(rA).Como el Dr. Andrew Zeitlin de CAASD's precisa, "debido a la carga de trabajo normalde los pilotos, no esperamos que pasen todo su tiempo que mira la pantalla. Es all

cuando est necesitado, pero ms importante, habla para arriba y los aconseja mientrasque necesitan hacer una maniobra para evitar una colisin."Aparte del diseo de la lgica, mucho del trabajo del inglete sobre TCAS implic elcrear y el funcionar de simulaciones de computadora para probar el sistema. "porque escostoso volar encuentro de la prueba," dice a Dr. Zeitlin, "hemos desarrollado algunasherramientas muy de gran alcance donde podemos generar millones de encuentro en lacomputadora y evaluar la lgica exhaustivo. Podemos tambin jugar datos traseros delradar del trfico ordinario y conseguir una sensacin para cmo el sistema trabaja ycunto interrupcin usted consigue cotidiano o en diversas localizaciones con trficoordinario." En la ocasin, el INGLETE tambin ha asistido al FAA y a otrasorganizaciones en la evaluacin de encuentro especial. "por ejemplo, si alguien tiene un

tiro errado y desean saber cules era el papel de TCAS's o qu TCAS habra hecho en elencuentro, podemos simular el encuentro y dar consejo," dice Zeitlin.


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El llevar los cielos: El Mandato Del congreso

De agosto el 31 de 1986, mientras que TCAS todava estaba en el desarrollo, una

colisin ocurri sobre Cerritos, California, implicando un Aeromexico Dc-9 y un avinpequeo de Piper que llevaba una familia de tres. El Dc-9 era descendente hacia elaeropuerto internacional de Los ngeles en los cielos claros, volando en 6.500 pies. ElPiper golpe la cola de DC-9's, el causar ambo avin para caer a plomo del cielo.El accidente dio lugar a las muertes de las 67 personas a bordo de los dos planos, ascomo 15 personas en la tierra. En las consecuencias de este accidente, el congresoaprob una ley que requera el FAA asignar el uso por mandato de TCAS. Antes de1993, todo el avin del portador que funcionaba dentro del espacio areo de ESTADOSUNIDOS con ms de 30 asientos de pasajero fue equipado del avin de TCAS II. con10 a 30 asientos fue requerido para emplear TCAS I.

Desarrollo para satisfacer necesidades de seguridad

Aunque las lneas areas utilizaban la versin ms avanzada 6,01 de la lgica de TCAS,algunas mejoras todava necesitaron ser llevadas a cabo. El sistema publicaba el rA enalgunas situaciones, tales como acercamiento final, cuando el trfico puede estar mscercano pero est con seguridad bajo control. Muchos pilotos vieron este el rA comofastidio. El sistema era bsicamente demasiado sensible, con uniforme innecesario deTA y del rA que era accionado por los transpondores en los puentes y las naves.Segn el Dr. Zeitlin, "haba una tendencia cada vez mayor entre pilotos a no hacer casodel consultivo, incluso cuando l no tena necesariamente conocimiento completo de lasituacin. Cada uno fue referido que un da no haran caso de uno que era necesario."En 1992, CAASD desarroll la versin 6,04 de la lgica para aliviar estos problemas.Las lneas areas del delta, el primer portador para utilizar voluntariamente la nuevalgica, divulgaron una reduccin de 80 por ciento en el rA. El ao siguiente, CAASDdesarroll una mejora adicional a la lgica, versin 6.0. Las lneas areas comenzarona equipar sus flotas de esta versin en 1994.

La Generacin Final

En 1997, CAASD acab el trabajo sobre un cambio importante final a la lgica deTCAS, versin 7. Fue aprobado por el comit de estndares de RTCA y el FAA, y es la

versin que ser instalada en todo el avin nuevo. Tambin ha sido adoptado por laorganizacin internacional de la aviacin civil (ICAO) como el estndar internacional.Inicialmente, la versin 7 ser instalada en europeo que sirve del avin y algunos otros

pases. Los portadores americanos que vuelan a estos pases tendrn que aumentar de6.0 a 7 en sus planos internacionales, y pueden aumentar voluntariamente el equipo yaen sus flotas de ESTADOS UNIDOS.

According to program manager David Lubkowski, who led CAASD's TCAS softwaredevelopment group, the version 7 logic should yield at least a 20 percent reduction inRAs over the previous version. "We also ran simulations using radar data from Europe,where they encounter more high-altitude en route conflicts," he said. "The new 7.0

software resulted in a 40 percent reduction in unnecessary RAs." The new logic alsosignificantly improves TCAS performance in several other important areas.


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CAASD personnel have conducted safety studies to evaluate the performance of eachsuccessive version of the TCAS logic. In a 1997 report on version 7, CAASD's Dr.Michael McLaughlin examined the reduced risk of collision in aircraft equipped withTCAS II versus the risk in aircraft without TCAS. Based on the likelihood of incursions

into a protected zone around aircraft with a radius of 500 feet and a height of 200 feet --defined as Critical Near Mid-Air Collisions (NMACs) -- McLaughlin concluded that"TCAS should reduce NMAC probability by at least 90 to 98 percent," depending onwhether one or both aircraft in an encounter are equipped with TCAS.Though NMACs, especially those involving commercial, passenger aircraft are alreadyextremely rare, McLaughlin notes that "TCAS is intended to reduce their probabilityeven further."Although the FAA has said that version 7 will be the final logic for TCAS, CAASDcontinues to work on many different air traffic control projects, and will undoubtedly

play a role in the development of any future collision avoidance systems.

tcas - traffic alert and collision avoidance system

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