AIRBORNE COLLISION AVOIDANCE SYSTEM (ACAS), AN OVERVIEW

henrychidiebere (60)in #steemstem • 7 years ago (edited)

Before the invention of airborne collision avoidance systems, there have been many records of nasty midair collisions caused by the collision of an aircraft against another aircraft. The first midair collision occurred on Saturday June 30, 1956 when two air planes, the TWA Flight 2 which headed to Kansas from LA at exactly 0901 and a United Airlines, Flight 718 which left LAX for Chicago at exactly 0904. Both of these flights maintained an altitude of 21,000. The duo collided on the boundaries of Grand Canyon National Park leaving no survivor. There were at total of 128 passengers aboard both planes and due to severity of the crash led to the development ACAS which changed the air control system entirely.

The Airborne Collision avoidance system was made to operate autonomously both in taking actions and in informing pilots of presence of another aircraft which might pose a collision threat after the incident that occurred on September 25, 1978.

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The collision occurred on a very bright day with clear skies. The photograph shown is the clear picture of Pacific Southwest Airlines (PSA) Flight 182 as it descended with a raging fire on the craft’s right wing. The PSA which had 135 passengers on-board was headed to San Diego from Sacramento at exactly 0720 and made a stop in LA. The captain who made contact with the controller before the crash had a sight of the airport when it descended to an altitude of 9,500. The crew were told to take a right hand pattern to a landing Runway 27 which was already in sight.

At the same time, another aircraft Cessna 172 which had students and their flight instructor aboard was approaching the airport northeast from its second practice instrument approach. These flights already had a radar communication system which was developed after the 1956 incident. The Cessna was in communication with the radar controller in the airport and so also was the second incoming jet, the PSA. The PSA was informed of the landing second aircraft with the controller saying

Additional traffic at 12 o’clock, three miles, now out of 1700”

And the captain operating the radio of the PSA responded "Traffic in sight" while the controller responded "OK" in affirmation. The Cessna was also alerted about the inbound PSA and was given instruction on what to do. The collision happened mainly because the Cessna received the information rather late and has the aircraft position changed from initial landing position of 070 degrees.

At that time, the Airborne Traffic Control system which was in an incomplete development stage was already warning the two crews about the impending danger but because the software system still contained some bugs and has the habit of raising false alarm, the controller and the crew ignored the warning alarm. Well the two crafts collided with the PSA getting serious hit underneath the right wing which gave out a bright orange flame as it took a dive towards the earth. The ground impact was also horrific, displacing about 22 houses, many automobiles and claimed the lives of 7 residents. If only the crews and the controller took warnings of the young ACAS into serious consideration.

Thanks to the combined efforts of NASA and other team of engineers that took up the completion and perfection of the ACAS technology starting from the year 1980. The ACAS actually prevents short-range metal-on-metal collision, hence another collision prevention system was developed to prevent collision from a longer range. This was the Airborne Separation Assurance System (ASAS) which maintains a standard of separation between two approaching crafts from a distance of up to 9.3km on a horizontal plane and a vertical distance of 1,000 feet above sea level.

image credit: sciencedirect

The implementation standards set for the ACAS which is contained in the volume 4 of the Convention on International
Civil Aviation (CICA) was only met by the version 7 and version 7.1 of the Traffic Collision Avoidance System V2 (TCAS II) and was developed by three manufacturers, the Honeywell, Rockwell Collins and Aviation Communication and Surveillance Systems as of 2009. In the United States, the TCAS is used interchangeably with ACAS.

The irregularities found in the ACAS at the initial stage was partly due to the incompatibility issues between minimal performance standards for the transponder system of the Air Traffic Control Radar Beacon System and the transponder system included in the TCAS. Transponders are electronic instrument which has the ability to produce response given a radio frequency interrogation. Transponders are given commands beginning with an oral code of “squawk”.

There has been several mid-air collision avoidance system in use by modern flights. TCAS is now a compulsory gadgets for our modern aircrafts even for private crafts. Some of these modern collision avoidance system including the TCAS are the FLARM, Portable Collision Avoidance System (PCAS), the Ground Proximity Warning System, the Terrain Awareness and Warning System, Synthetic Vision, Obstacle Collision Avoidance System, etc.

The Synthetic Vision System was developed as result of joint efforts of NASA and United States Air Force back in the early 1980s.

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The synthetic vision helps pilot provide a detailed information of the terrain pictorially in 3D allowing pilots get better view of their geographical location, obstacle and many other information concerning their immediate environment. Synthetic vision system is composed of a geographical database, a display system and an image generator system. Synthetic Vision System are not only used on pilot controlled aircrafts but also in remote controlled vehicles like the High Maneuvability Aeriel Testbed (HiMAT). The image shown (left) is the synthetic vision of the HiMAT downlinked to a remote cockpit.

FLARM is a collision avoidance system used for short-range communication system used to alert pilots of a potential collision. For FLARM to control collision situations, the two flights must have the technology installed since it is not compatible with ATC.

Image credit: Wikipedia

Flights fitted with the FLARM device interchange position and altitude information obtained from two sensors, the GPS and Barometer. Once this information is broadcasted, motion prediction algorithm is carried out and this prediction is enough to predict potential collision for up to 50 flights and give out both visual and aural warnings to flight crews. FLARM has the advantage of being affordable, ease of installation and relatively power efficient.

The Airborne Radar (AR) is one of the simplest of the transponders and can accurately detect the relative position of another aircraft. The use of AR requires a good knowledge of geolocations. Unlike other transponders, AR only give notification and location of another aircraft but needs to work with other collision avoidance system to work effectively since it lacks the ability to advice crew members on specific directions to take.

The Ground Proximity Warning System was developed after series of air accidents cause by the collision of aircraft with terrains like hills, water and obstacles.

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These accidents wasn’t due to incapable crews or poorly maintained flights but because the crew members are unaware of the impending obstacles. The proximity warning system alerts pilots whenever their aircraft are in the danger of colliding with obstacle or flying into elevated ground without activating proper landing system. The Terrain Awareness and Warning System is said to be the advanced version of proximity warning system.

CONCLUSION

The field of electronics has been one of the backbones of flight control systems. Before the advent of collision control systems, many deaths and property losses were recorded due to flight collisions. The TCAS is the only collision avoidance system that meets the implementation standard of the International Civil Aviation Organization as of 2009 though other collision avoidance system are still in use which some were discussed herein. The addition of at least on Airborne Collision Avoidance system is now compulsory even for private flights and is being enforced by Aviation agencies worldwide.

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