Airborne Collision Avoidance System
Encyclopedia
An airborne collision avoidance system (ACAS) is an aircraft
system that operates independently of ground-based equipment and air traffic control
in warning pilots of the presence of other aircraft that may present a threat of collision. If the risk of collision is imminent, the system indicates a manoeuvre that will reduce the risk of collision. ACAS standards and recommended practices are mainly defined in annex 10, volume IV, of the Convention on International Civil Aviation
.http://www.eurocontrol.int/msa/public/standard_page/ACAS_ICAO_Provisions.html
A distinction is increasingly being made between ACAS and ASAS (airborne separation assurance system). ACAS is being used to describe short-range systems intended to prevent actual metal-on-metal collisions. In contrast, ASAS is being used to describe longer-range systems used to maintain standard en route separation between aircraft (5 nm {9.25 km} horizontal /1000' {305 m} vertical).
As of 2009, the only implementations that meets the ACAS II standards set by ICAO are Versions 7.0 and 7.1 of TCAS II (Traffic Alert and Collision Avoidance System
) produced by three manufacturers: Rockwell Collins
, Honeywell
and ACSS (Aviation Communication & Surveillance Systems; an L-3 Communications
and Thales Avionics
company).
As of 1973, the United States Federal Aviation Administration
(FAA) standard for transponder minimal operational performance, Technical Standards Order (TSO) C74c, contained errors which affect both air traffic control radar beacon system
(ATCRBS) radar and Traffic Alert and Collision Avoidance System
(TCAS) abilities to detect aircraft transponders. First called "The Terra Problem", there have since been individual FAA Airworthiness Directive
s issued against various transponder manufacturers in an attempt to repair the operational deficiencies, to enable newer radars and TCAS systems to operate. Unfortunately, the defect is in the TSO, and the individual corrective actions to transponders have led to significant differences in the logical behavior of transponders by make and mark, as proven by an FAA study of in-situ transponders.
AIS-P is a modification which both corrects the transponder deficiencies (the transponder will respond to all varieties of radar and TCAS), then adds an Automatic Independent Surveillance with Privacy augmentation. The AIS-P protocol does not suffer from the saturation issue in high density traffic, does not interfere with the Air Traffic Control (ATC) radar system or TCAS, and conforms to the internationally approved Mode S data packet standard. It awaits member country submission to the ICAO as a requested approval.
Modern aircraft
can use several types of collision avoidance systems to prevent unintentional contact with other aircraft, obstacles, or the ground:
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
system that operates independently of ground-based equipment and air traffic control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
in warning pilots of the presence of other aircraft that may present a threat of collision. If the risk of collision is imminent, the system indicates a manoeuvre that will reduce the risk of collision. ACAS standards and recommended practices are mainly defined in annex 10, volume IV, of the Convention on International Civil Aviation
Convention on International Civil Aviation
The Convention on International Civil Aviation, also known as the Chicago Convention, established the International Civil Aviation Organization , a specialized agency of the United Nations charged with coordinating and regulating international air travel...
.http://www.eurocontrol.int/msa/public/standard_page/ACAS_ICAO_Provisions.html
A distinction is increasingly being made between ACAS and ASAS (airborne separation assurance system). ACAS is being used to describe short-range systems intended to prevent actual metal-on-metal collisions. In contrast, ASAS is being used to describe longer-range systems used to maintain standard en route separation between aircraft (5 nm {9.25 km} horizontal /1000' {305 m} vertical).
As of 2009, the only implementations that meets the ACAS II standards set by ICAO are Versions 7.0 and 7.1 of TCAS II (Traffic Alert and Collision Avoidance System
Traffic Collision Avoidance System
A traffic collision avoidance system or traffic alert and collision avoidance system is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft...
) produced by three manufacturers: Rockwell Collins
Rockwell Collins
Rockwell Collins, Inc. is a large United States-based international company headquartered in Cedar Rapids, Iowa, primarily providing aviation and information technology systems and services to governmental agencies and aircraft manufacturers.- History :...
, Honeywell
Honeywell
Honeywell International, Inc. is a major conglomerate company that produces a variety of consumer products, engineering services, and aerospace systems for a wide variety of customers, from private consumers to major corporations and governments....
and ACSS (Aviation Communication & Surveillance Systems; an L-3 Communications
L-3 Communications
L-3 Communications Holdings, Inc. is a company that supplies command and control, communications, intelligence, surveillance and reconnaissance systems and products, avionics, ocean products, training devices and services, instrumentation, space, and navigation products. Its customers include...
and Thales Avionics
Thales Group
The Thales Group is a French electronics company delivering information systems and services for the aerospace, defense, transportation and security markets...
company).
As of 1973, the United States Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
(FAA) standard for transponder minimal operational performance, Technical Standards Order (TSO) C74c, contained errors which affect both air traffic control radar beacon system
Air Traffic Control Radar Beacon System
The air traffic control radar beacon system is a system used in air traffic control to enhance surveillance radar monitoring and separation of air traffic. ATCRBS assists ATC surveillance radars by acquiring information about the aircraft being monitored, and providing this information to the...
(ATCRBS) radar and Traffic Alert and Collision Avoidance System
Traffic Collision Avoidance System
A traffic collision avoidance system or traffic alert and collision avoidance system is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft...
(TCAS) abilities to detect aircraft transponders. First called "The Terra Problem", there have since been individual FAA Airworthiness Directive
Airworthiness Directive
An Airworthiness Directive is a notification to owners and operators of certified aircraft that a known safety deficiency with a particular model of aircraft, engine, avionics or other system exists and must be corrected....
s issued against various transponder manufacturers in an attempt to repair the operational deficiencies, to enable newer radars and TCAS systems to operate. Unfortunately, the defect is in the TSO, and the individual corrective actions to transponders have led to significant differences in the logical behavior of transponders by make and mark, as proven by an FAA study of in-situ transponders.
AIS-P is a modification which both corrects the transponder deficiencies (the transponder will respond to all varieties of radar and TCAS), then adds an Automatic Independent Surveillance with Privacy augmentation. The AIS-P protocol does not suffer from the saturation issue in high density traffic, does not interfere with the Air Traffic Control (ATC) radar system or TCAS, and conforms to the internationally approved Mode S data packet standard. It awaits member country submission to the ICAO as a requested approval.
Modern aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
can use several types of collision avoidance systems to prevent unintentional contact with other aircraft, obstacles, or the ground:
- Airborne RadarRadarRadar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
can detect the relative location of other aircraft, and has been in military use since World War IIWorld War IIWorld War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, when it was introduced to help night fighters (such as the de Havilland MosquitoDe Havilland MosquitoThe de Havilland DH.98 Mosquito was a British multi-role combat aircraft that served during the Second World War and the postwar era. It was known affectionately as the "Mossie" to its crews and was also nicknamed "The Wooden Wonder"...
and Messerschmitt Bf 110Messerschmitt Bf 110The Messerschmitt Bf 110, often called Me 110, was a twin-engine heavy fighter in the service of the Luftwaffe during World War II. Hermann Göring was a proponent of the Bf 110, and nicknamed it his Eisenseiten...
) locate bombers. While larger civil aircraft carry weather radarWeather radarWeather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...
, sensitive anti-collision radar is rare in non-military aircraft.
- a Traffic alert and Collision Avoidance SystemTraffic Collision Avoidance SystemA traffic collision avoidance system or traffic alert and collision avoidance system is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft...
(TCAS), which actively interrogates the transponderTransponderIn telecommunication, the term transponder has the following meanings:...
s of other aircraft and negotiates collision-avoidance tactics with them in case of a threat. TCAS systems are relatively expensive, and tend to appear only on larger aircraft. They are effective in avoiding collisions only with other aircraft that are equipped with functioning transponders with altitude reporting.
- a Portable Collision Avoidance System
Portable Collision Avoidance SystemPortable Collision Avoidance System is an aircraft collision avoidance system similar in function to traffic collision avoidance system...
(PCAS) is a less expensive, passive version of TCAS designed for general aviationGeneral aviationGeneral aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...
use. PCAS systems do not actively interrogate the transponders of other aircraft, but listen passively to responses from other interrogations. PCAS is subject to the same limitations as TCAS, but also is ineffective if there is not at least one system (such as air traffic control or a TCAS-equipped aircraft) interrogating another aircraft's transponder.
- FLARMFLARMFLARM is an electronic device to selectively alert pilots to potential collisions between aircraft. It is not formally an implementation of ADS-B, as it is optimised for the specific needs of small aircraft such as gliders, not for long-range communication or ATC interaction.FLARM obtains its...
is a small-size, low-cost, low-power device (commonly used in gliders or other light aircraft) which broadcasts its own position and speed vector (as obtained with an integrated GPS) over a license-free ISM band radio transmission. At the same time it listens to other devices based on the same standard. Intelligent motion prediction algorithms predict short-term conflicts and warn the pilot accordingly by acoustical and visual means. FLARM incorporates a high-precision WAAS 16-channel GPS receiver and an integrated low-power radio transceiver. Static obstacles are included in FLARM's database. No warning is given if an aircraft does not pose an immediate threat.
- a Ground proximity warning systemGround Proximity Warning SystemA ground proximity warning system is a system designed to alert pilots if their aircraft is in immediate danger of flying into the ground or an obstacle. The United States Federal Aviation Administration defines GPWS as a type of terrain awareness warning system...
(GPWS), or Ground collision warning system (GCWS), which uses a radar altimeterRadar altimeterA radar altimeter, radio altimeter, low range radio altimeter or simply RA measures altitude above the terrain presently beneath an aircraft or spacecraft...
to detect proximity to the ground or unusual descent rates. GPWS is common on civil airliners and larger general aviationGeneral aviationGeneral aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...
aircraft.
- a Terrain awareness and warning systemTerrain awareness and warning systemA terrain awareness and warning system aims to prevent "Controlled Flight Into Terrain" accidents. The actual systems in current use are known as ground proximity warning system and enhanced GPWS. The U.S. Federal Aviation Administration developed the TAWS term to encompass all current and...
(TAWS) uses a digital terrain map, together with position information from a navigation system such as GPS, to predict whether the aircraft's current flight path could put it in conflict with obstacles such as mountains or high towers, that would not be detected by GPWS (which uses the ground elevation directly beneath the aircraft).
- Synthetic visionSynthetic visionA Synthetic Vision System is a computer-mediated reality system for aerial vehicles, that uses 3D to provide pilots with clear and intuitive means of understanding their flying environment....
provides pilots with a computer-generated simulation of their outside environment for use in low or zero-visibility situations.
- Obstacle Collision Avoidance SystemObstacle Collision Avoidance SystemThe Obstacle Collision Avoidance System is designed to alert pilots if their aircraft is in immediate danger of flying into an obstacle. OCAS uses a low power ground based radar to provide detection and tracking of an aircraft's proximity to an obstacle such as a power line crossing, telecom...
is a ground based system that uses a low powered radar mounted on or near the obstacle. The radar detects aircraft in the proximity of the obstacle and firstly warns aircraft via flashing medium intensity lights and secondly warns aircraft of the obstacle via a VHF broadcast. No additional equipment is required on board the aircraft. Large, sophisticated aircraft may use several or all of these systems, while a small general aviation aircraft might have only PCAS or benefit from the OCAS system, or no collision-avoidance system at all (other than the pilot's situational awareness).
See also
- AvionicsAvionicsAvionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...
- Air traffic controlAir traffic controlAir traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
- Collision avoidanceCollision avoidanceIn spaceflight, collision avoidance is the process of preventing a spacecraft from colliding with any other vehicle or object.-Launch Windows:Collision avoidance, or COLA is a concern during spaceflight launch windows...
(disambiguation) - Acronyms and abbreviations in avionicsAcronyms and abbreviations in avionics-A:*ACARS: Aircraft Communications Addressing and Reporting System.*ACAS: Airborne Collision Avoidance System.*ACP: Audio Control Panel.*ACS: Audio Control System.*ADAHRS: Air Data and Attitude Heading Reference System.*ADC: Air Data Computer....
- TCASTraffic Collision Avoidance SystemA traffic collision avoidance system or traffic alert and collision avoidance system is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft...