The definition given to runway incursions has been slightly varying in various organizations that are concerned with safety situations at the airports. According to the Federal Aviation Administration (FAA), runway incursion is defined as any occurrence at an airport involving an aircraft, vehicle, person, or object on the ground that creates a collision hazard or results in a loss of separation as directed by air traffic requirements) with an aircraft taking off, intending to take off, landing or intending to land (Peggy, 2008, Para 4). On the other hand, the International Civil Aviation Organization (ICAO) defines runway incursion as any occurrence at an aerodrome involving the incorrect presence of an air craft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft (Peggy, 2008, Para 5). However, according to Peggy, the FAA has expanded its definition in order to create harmony with the ICAOs definition of the runway incursion.
This was an important step as incursions at airports have to adopt universal connotations so as to be able to address the problem from a standardized approach. Incidences of runway incursions are usually costly for the airlines and pose a great risk of ending in fatalities. However, the trend has been worrying with escalating tendencies of runway incursions being reported. This scenario has continued to present a daunting challenge to the Air Traffic Control (ATC) world. In reaction to the rapid increase of the incursion incidents, the National Air and Space Administration (NASA) and the FAA have started developing theories and systems aimed at preventing the runway incursions.
Runway incursion has been defined differently with various organizations that are concerned with safety issues at the airports. According to the Federal Aviation Administration (FAA), runway incursion is defined as any occurrence at an airport involving an aircraft, vehicle, person, or object on the ground that creates a collision hazard or results in a loss of separation as directed by air traffic requirements) with an aircraft taking off, intending to take off, landing or intending to land (Peggy, 2008, Para 4).
On the other hand, the International Civil Aviation Organization (ICAO) defines runway incursion as any occurrence at an aerodrome involving the incorrect presence of an air craft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft (Peggy, 2008, Para 5). However, according to Peggy, FAA has expanded its definition in order to create harmony with the ICAOs definition of the runway incursion. Incidences of runway incursions are usually costly for the airlines and pose a great risk of ending in fatalities. Over the past two decades, runway incursions have been rapidly increasing, for instance, in the period between 1988 and 2002, incursions incidents rose from 187 to 337 respectively (Keller, 2003).
This incredible increase has been witnessed despite the insignificant increase in the number of taxiing aircrafts at the airports. This scenario has continued to present a daunting challenge to the Air Traffic Control (ATC) world. In reaction to the rapid increase of the incursion incidents, the National Air and Space Administration (NASA) and FAA have started developing theories and systems aimed at preventing the occurrences. The subsystems have been designed in such a manner that they incorporates optical data and moving-map displays in the cock-pits of runway-taxiing aircraft and sensor systems that send aircraft location data to airport communication towers, (Keller, 2003, Para 2).
This paper is aimed at investigating the various types of runway incursions and the prevention systems that have been adopted by FAA and NASA.
Runway Incursion Scenarios
Runway incursions have at times led to fatal accidents with significant loss of human life having been recorded. This is not a new problem but what is worrying is the increasing trend in the incursions at our airports. The FAA has divided the potentiality of runway occurrence into four categories which includes pilot deviations, operational errors, operational deviations, and vehiclepedestrian deviations. Pilot deviations are best described as any action of the pilot that has a tendency to result in the violation of the FAA regulations.
In precision, pilot deviations occurs when the pilot makes a maneuver that leads to the divergence from a conventional flight plan or course alteration without notification from the ATC or clearance. The operational errors happens when an aircraft unintentionally losses separation (causes a collision or comes very close to causing a collision) with another plane while taxiing on a runway or when an aircraft attempts to land on or take off from a runway that has been closed (Keller, 2003, Para 6). Operational deviations result from an aircraft entering a protected airspace without consent. Lastly, vehicle or pedestrian deviation happens when people andor vehicles from outside makes an entrance to designated areas for aircraft traffic without having attained proper authorization (Keller, 2003).
Causes
The several incursions discussed above can generally be attributed to two main factors. There is lack of clear, absolute know how by both the pilots and the ATC employees who are supposed to determine the place for the aircraft and ground automobiles are to be located on the airport ground at any given moment. There is also lack of efficiency and effectiveness in communication and coordination when it comes to ATC and taxiing, take-off, and landing of the aircraft. However, these causative factors can further be divided to address specific concepts that may result in runway incursions. A report prepared by the Transport Canada revealed a number of factors that can result in runway incursions. The factors highlighted includes increase in traffic volume, capacity-enhancing procedures, airport layout, complexity and, not surprisingly, human factors (Fisher, 2009, Para 5). In a study done in Canada, it was observed that there was a correlation between an increase in the number of incursions and the corresponding increase in the number of traffic. In an effort to tame the increase in traffic, there were procedures that included the parallel runway operations, Simultaneous Intersection Runway Operations (SIRO) or Land Short Operations (LAHSO) which were introduced. Upon computation of these procedures, it was discovered that the capacity-enhancing procedures had a revealing impact on the incursion possibilities. These procedures provide numerous opportunities in which an incursion can occur (Fisher, 2009).
Another contributing factor to runway incursions can be traced in the airport layouts whose structures have been altered to accommodate the current and the forecast increases in the number of traffic. This has in most cases resulted in more intricate aerodrome environment which is susceptible to runway incursions. The resulting complexity from the combined factors has been identified as a major cause in the upsurge of the runway incursion potential with studies revealing that the overall complexity is more influential than the individual sum of its constituents. Whereas the other factors only present the potentiality of the occurrence of a runway incursion, it is the human error that turns this potential into an actual happening. According to Fisher, complexity, lack of familiarity with the airport layout, communications difficulties, distractions, and other factors all contribute to making flight crew and air controllers more vulnerable to committing errors (Para, 19).
Classification of Severity of Runway Incursions
Severity classification was arrived at by the ICAO in an effort to produce and record an evaluation of each incident of runway incursion. A Runway Incursion Severity Classification (RISC) calculator was invented to aid in the assessment of severity of the runway incursions. Severity of an incursion is an important aspect of risk management in which case risk is seen as the function of the severity of the resultant consequence and the possibility of its reappearance. In spite of the severity of the incident, all runway incursions have to be properly investigated to establish the causes and the contributing factors so as preventive measures are taken to inhibit the recurrence of a similar incident. ICAO has classified the runway incursions into five categories labeled A to E depending on the severity. The A category is the most serious in which case an actual collision is barely avoided. Category B involves an incident where separation is reduced and there is a considerable potential for collision, which may result in a timely evasive response that avoids the collision. Category C represents a situation where there is ample time andor distance to keep away from a collision. Class D of runway incursions presents a situation that is in line with the definition of the concept for instance, the incorrect presence of an automobile, an individual, or and aircraft on the prohibited area of the airport which does not pose any immediate safety consequences. Last but not least, category E involves the availability of inadequate or uncertain or contradictory evidence which precludes the severity assessment (ICAO, 2007).
Runway Incursions
According to the Administrator of FAA, the primary mission of the FAA is safety. FAA boasts of the provision of some of the safest modes of transport in the world today. Nevertheless, has to continue with vigilance in addressing the ever emergent issues concerning the safety of the airports. The Administrator recognized that dealing with the safety risks in the National Airspace System was not an easy task as it requires a logical approach which integrates safety issues into dutiful undertakings in the airport environment (FAA, 2009). According to the Runway Safety Report of September, 2007, there were four categories-A runway incursions between the years 2003 and 2006. In the same period, there were 1,306 runway incursions being recorded in general (FAA, 2009).
Runway incursions incidents and near incidents are frequently reported and this has raised great concerns among the national aviation safety officials. The steady growth of runway incursion incidences in the past few years has seen an increase of well up to 60 being recorded. In 1999, there were 320 incidents being recorded and during the first half of 2000, the incidents were increasing at a record setting pace (Allen, 2008). The FAA launched a special initiative aimed at improving operations at the airport surfaces whereas NASA is working on the technology that will considerably help the FAA in its efforts. With the aid of industry team, NASAs Aviation Safety Program is involved in the designing of advanced flight deck display systems to help in curbing the escalating rates of runway incursion incidents. The system is composed of technologies which will be engaged in the provision of fundamental airborne and ground information that includes topography, ground obstacles, and air traffic among other aspects that can be helpful in avoiding runway incursion (Allen, 2008).
Runway Incursion Prevention Systems
There are several solutions that have been designed to address the runway incursion problem in airports across the world. The suggested solutions include the stationary ground ladder systems located on airport surfaces. The radar systems have automatic track taxiing aircraft, and a Global Positioning System (GPS) unit found within the aircraft and uses the cluster of orbiting satellites to identify the location of the aircraft with a margin error of between 1 to 2 meters. In the event that these systems fail, the pilots and the ATC personnel are likely to receive wrong information and the risk for an incursion becomes high than even when the devise was not in use. To address this challenge, the Multi-static Dependant Surveillance (MDS) system was invented. This system is extremely powerful as it uses a combination of the highly accurate GPS technique and another technique better known as multilateration. Even though multilateration is not as accurate as the GPS technique with the positioning accuracy of between 5 to 10 meters, its efficiency as a secondary airport surveillance technique cannot be wished away. The MDS system has at least three remote sensor units (RUs) which are positioned around an airport surface to identify certain emissions of radio frequencies (RF) from taxiing, landing, and taking-off aircraft. Every aircraft that operates on or closer to an airport surface are outfitted with a transponder unit capable of sending out a radio frequency signal once every second designated at a frequency of 1090Mega Hertz. The signals are usually encoded as Automatic Dependent Surveillance Broadcast (ADS-B) messages (Keller, 2003). .
The ADS-B is a more recent format of aviation positional data encoding and transmission which ensures aircrafts regularly transmits their locations directly to any other aircrafts in the surrounding. The messages have data on the latitude and longitude of the aircraft which is gotten from the GPS unit, and also the velocity and the altitude of the aircraft. Each RU receive these signals, decoding and time-stamping them with a value known as a time-of-reception value which is enabled by an in-built clock that is matched all RUs found in the system. Each RU then has to attach the time stamp value at the last part of the decoded message, and return the transmissions back to a central target processor (TP) which is normally found in the ATC tower in close proximity. In this manner, MDS system is credited for providing a highly accurate GPS solution based on a target aircraft. It also gets the crucial information that is required for independent triangulation of the aircrafts position by the use of multilateration. Multilateration can be described as a positioning technique that utilizes a mathematical concept referred to as Time Difference of Arrival (TDOA) in estimating the location of a target (Keller, 2003).
Another surveillance system that has been adopted uses the inductive loop technology. There are several problems associated with the existing radar based and GPS solutions discussed above. The two main problems of the latter are identified as disruptions in the accuracy because of RF signal reflections off the large structures, and the impediment to the capability of ATC personnel to scan the whole of the airport surface visually and track down any taxiing aircraft. It is due to these shortcomings that the inductive loop technology system were invented and used in some of the airports across the world. The LOT system also known as the inductive loop sensor subsystem is a typical example of the inductive loop system that consists of a sensor, a loop detection component, and a classification and a tracking element. According to Edward, there are four 135 by 10 inductive loops which are located beneath the airport surface in rectangular-shaped saw cuts providing the sensing component of the system. Every loop has three turns of encapsulated and trapped wires which are situated underneath the runway in a groove of about 1.5 deep and 0.25 wide. The loops are subsequently enclosed with a backer rod and finally the groove is closed with epoxy (Keller, 2003).
The loop detection component (LDC) is placed within a controller cabinet, which in most cases is to be found within 500 to 1000 ft. from the loop. A lead-in wire joins the LDC with every loop. In the event that an aircraft or a vehicle passes over the loop, an inductance variation takes place within the loop, creating a shape-based signal that is uniquely different from the various aircrafts. As the varying inductance signal goes beyond the loop detector threshold value, the LDC responds by declaring target detection. The LDC relays this time varying signal to a Classification and Tracking Component (CTC) server computer over an RS-232 interface using a spread spectrum RF communication connection. The CTC then goes ahead and identifies the target basing on the detections of the inductive signals. With the aid of the various target-tracking algorithms, the CTC continues to display the movements of the target on the output display screen when it passes above the subsequent inductive loops, integrating the tracking results from other sensor input systems (such as radar units, MDS systems, etc) to display a high accurate tracking of the aircraft (Keller, 2003, Para 20). Thus LOT can be credited for the provision of full runway tracking coverage when the units are fitted all around the airport surface (Keller, 2003).
Many runway incursions are believed to occur because of inadequate tracking coverage of airport surface, but still they can occur because of erroneous location and approach data when an aircraft attempts to touch down on a runway. To address this problem, the Local Area Augmentation System (LAAS) has been advanced. This is a different GPS- based (DGPS) precision approach and landing system consisting of three subsystems a GPS satellite, a grounded subsystem with reference antennas placed around the airport runway surface, and a data processing subsystem onboard the aircraft (Keller, 2003 Para 23). According to Keller, the GPS receivers in the aircraft and the reference antennas are designed to use a cluster of the GPS satellites in pinpointing their own locations. The data on the location which is determined by the antennas found in the grounded subsystem is put to analysis by a computerized system in order to get a discrepancy correlation and reliable data on the subsequent runway approach that is to be allocated to the aircraft. All this is relayed back to the processing subsystem that is inbuilt in the aircraft via a means of Very High Frequency (VHF) Data Broadcast apparatus. Upon receiving this differential correlation and reliable data, the processing subsystem uses the data in combination with its position information that is gotten directly from the GPS system so as to differentially calculate refined location estimates of the runway approach. This technique greatly reduces the possibility for inaccurate location and approach data with the landing aircraft having more runway approach commands in precision (Keller, 2003).
All the other systems discussed above aid in preventing incursions. However, it usually takes long before an action is taken by the ATC personnel and therefore the PathProx system has been advanced to address this problem. PathProx refers to an onboard surveillance system that is modeled to recognize early conditions that are potential for runway incursions, providing pilots and ground automobile operators with enough time to avoid incursions. This system uses data broadcasts on air traffic positioning courtesy of the Traffic Information Service-Broadcast system (TIS-B) or the Automatic Dependant Surveillance-Broadcast system (ADS-B) which obtains the traffic information from exterior surveillance sources. The PathProx system is so complex that it can handle forty different runway incursion incidents at a given time (Keller, 2003). As technology improves, so does our preventive measures on incursion at the runway. The most recent runway incursion preventive technology has been adopted in Alaska and is referred to as the Runway Awareness and Advisory System (RAAS). The system is essentially a ground proximity warning system that uses satellite technology to precisely determine the aircrafts actual position on the apron and taxiways. It also alerts the crew regarding a potential collision with other aircrafts or ground automobiles. It also provides the pilots with a moving map cock pit display showing local terrain (Broadbent, 2008, Para6). This technology was developed by Honeywell and is thought to have offered a major breakthrough in incursion prevention (Broadbent, 2008).
Runway incursions have posed a significant problem in airports across the world. However, this challenge has been handled accordingly with some achievements being noticed. However, it is important to note that all the prevention systems discussed above have failed to some extent in precision and continuous aircraft tracking. This can be positively taken to encourage research activities that might result into what has continued to be seen as ideal. As we have noted, advances in technology seems to be improving the situation bit by bit. It is my hope that the continuous improvement will finally take us to a position where by runway safety will no longer preoccupy the minds of ATC personnel and the aircraft pilots.
This was an important step as incursions at airports have to adopt universal connotations so as to be able to address the problem from a standardized approach. Incidences of runway incursions are usually costly for the airlines and pose a great risk of ending in fatalities. However, the trend has been worrying with escalating tendencies of runway incursions being reported. This scenario has continued to present a daunting challenge to the Air Traffic Control (ATC) world. In reaction to the rapid increase of the incursion incidents, the National Air and Space Administration (NASA) and the FAA have started developing theories and systems aimed at preventing the runway incursions.
Runway incursion has been defined differently with various organizations that are concerned with safety issues at the airports. According to the Federal Aviation Administration (FAA), runway incursion is defined as any occurrence at an airport involving an aircraft, vehicle, person, or object on the ground that creates a collision hazard or results in a loss of separation as directed by air traffic requirements) with an aircraft taking off, intending to take off, landing or intending to land (Peggy, 2008, Para 4).
On the other hand, the International Civil Aviation Organization (ICAO) defines runway incursion as any occurrence at an aerodrome involving the incorrect presence of an air craft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft (Peggy, 2008, Para 5). However, according to Peggy, FAA has expanded its definition in order to create harmony with the ICAOs definition of the runway incursion. Incidences of runway incursions are usually costly for the airlines and pose a great risk of ending in fatalities. Over the past two decades, runway incursions have been rapidly increasing, for instance, in the period between 1988 and 2002, incursions incidents rose from 187 to 337 respectively (Keller, 2003).
This incredible increase has been witnessed despite the insignificant increase in the number of taxiing aircrafts at the airports. This scenario has continued to present a daunting challenge to the Air Traffic Control (ATC) world. In reaction to the rapid increase of the incursion incidents, the National Air and Space Administration (NASA) and FAA have started developing theories and systems aimed at preventing the occurrences. The subsystems have been designed in such a manner that they incorporates optical data and moving-map displays in the cock-pits of runway-taxiing aircraft and sensor systems that send aircraft location data to airport communication towers, (Keller, 2003, Para 2).
This paper is aimed at investigating the various types of runway incursions and the prevention systems that have been adopted by FAA and NASA.
Runway Incursion Scenarios
Runway incursions have at times led to fatal accidents with significant loss of human life having been recorded. This is not a new problem but what is worrying is the increasing trend in the incursions at our airports. The FAA has divided the potentiality of runway occurrence into four categories which includes pilot deviations, operational errors, operational deviations, and vehiclepedestrian deviations. Pilot deviations are best described as any action of the pilot that has a tendency to result in the violation of the FAA regulations.
In precision, pilot deviations occurs when the pilot makes a maneuver that leads to the divergence from a conventional flight plan or course alteration without notification from the ATC or clearance. The operational errors happens when an aircraft unintentionally losses separation (causes a collision or comes very close to causing a collision) with another plane while taxiing on a runway or when an aircraft attempts to land on or take off from a runway that has been closed (Keller, 2003, Para 6). Operational deviations result from an aircraft entering a protected airspace without consent. Lastly, vehicle or pedestrian deviation happens when people andor vehicles from outside makes an entrance to designated areas for aircraft traffic without having attained proper authorization (Keller, 2003).
Causes
The several incursions discussed above can generally be attributed to two main factors. There is lack of clear, absolute know how by both the pilots and the ATC employees who are supposed to determine the place for the aircraft and ground automobiles are to be located on the airport ground at any given moment. There is also lack of efficiency and effectiveness in communication and coordination when it comes to ATC and taxiing, take-off, and landing of the aircraft. However, these causative factors can further be divided to address specific concepts that may result in runway incursions. A report prepared by the Transport Canada revealed a number of factors that can result in runway incursions. The factors highlighted includes increase in traffic volume, capacity-enhancing procedures, airport layout, complexity and, not surprisingly, human factors (Fisher, 2009, Para 5). In a study done in Canada, it was observed that there was a correlation between an increase in the number of incursions and the corresponding increase in the number of traffic. In an effort to tame the increase in traffic, there were procedures that included the parallel runway operations, Simultaneous Intersection Runway Operations (SIRO) or Land Short Operations (LAHSO) which were introduced. Upon computation of these procedures, it was discovered that the capacity-enhancing procedures had a revealing impact on the incursion possibilities. These procedures provide numerous opportunities in which an incursion can occur (Fisher, 2009).
Another contributing factor to runway incursions can be traced in the airport layouts whose structures have been altered to accommodate the current and the forecast increases in the number of traffic. This has in most cases resulted in more intricate aerodrome environment which is susceptible to runway incursions. The resulting complexity from the combined factors has been identified as a major cause in the upsurge of the runway incursion potential with studies revealing that the overall complexity is more influential than the individual sum of its constituents. Whereas the other factors only present the potentiality of the occurrence of a runway incursion, it is the human error that turns this potential into an actual happening. According to Fisher, complexity, lack of familiarity with the airport layout, communications difficulties, distractions, and other factors all contribute to making flight crew and air controllers more vulnerable to committing errors (Para, 19).
Classification of Severity of Runway Incursions
Severity classification was arrived at by the ICAO in an effort to produce and record an evaluation of each incident of runway incursion. A Runway Incursion Severity Classification (RISC) calculator was invented to aid in the assessment of severity of the runway incursions. Severity of an incursion is an important aspect of risk management in which case risk is seen as the function of the severity of the resultant consequence and the possibility of its reappearance. In spite of the severity of the incident, all runway incursions have to be properly investigated to establish the causes and the contributing factors so as preventive measures are taken to inhibit the recurrence of a similar incident. ICAO has classified the runway incursions into five categories labeled A to E depending on the severity. The A category is the most serious in which case an actual collision is barely avoided. Category B involves an incident where separation is reduced and there is a considerable potential for collision, which may result in a timely evasive response that avoids the collision. Category C represents a situation where there is ample time andor distance to keep away from a collision. Class D of runway incursions presents a situation that is in line with the definition of the concept for instance, the incorrect presence of an automobile, an individual, or and aircraft on the prohibited area of the airport which does not pose any immediate safety consequences. Last but not least, category E involves the availability of inadequate or uncertain or contradictory evidence which precludes the severity assessment (ICAO, 2007).
Runway Incursions
According to the Administrator of FAA, the primary mission of the FAA is safety. FAA boasts of the provision of some of the safest modes of transport in the world today. Nevertheless, has to continue with vigilance in addressing the ever emergent issues concerning the safety of the airports. The Administrator recognized that dealing with the safety risks in the National Airspace System was not an easy task as it requires a logical approach which integrates safety issues into dutiful undertakings in the airport environment (FAA, 2009). According to the Runway Safety Report of September, 2007, there were four categories-A runway incursions between the years 2003 and 2006. In the same period, there were 1,306 runway incursions being recorded in general (FAA, 2009).
Runway incursions incidents and near incidents are frequently reported and this has raised great concerns among the national aviation safety officials. The steady growth of runway incursion incidences in the past few years has seen an increase of well up to 60 being recorded. In 1999, there were 320 incidents being recorded and during the first half of 2000, the incidents were increasing at a record setting pace (Allen, 2008). The FAA launched a special initiative aimed at improving operations at the airport surfaces whereas NASA is working on the technology that will considerably help the FAA in its efforts. With the aid of industry team, NASAs Aviation Safety Program is involved in the designing of advanced flight deck display systems to help in curbing the escalating rates of runway incursion incidents. The system is composed of technologies which will be engaged in the provision of fundamental airborne and ground information that includes topography, ground obstacles, and air traffic among other aspects that can be helpful in avoiding runway incursion (Allen, 2008).
Runway Incursion Prevention Systems
There are several solutions that have been designed to address the runway incursion problem in airports across the world. The suggested solutions include the stationary ground ladder systems located on airport surfaces. The radar systems have automatic track taxiing aircraft, and a Global Positioning System (GPS) unit found within the aircraft and uses the cluster of orbiting satellites to identify the location of the aircraft with a margin error of between 1 to 2 meters. In the event that these systems fail, the pilots and the ATC personnel are likely to receive wrong information and the risk for an incursion becomes high than even when the devise was not in use. To address this challenge, the Multi-static Dependant Surveillance (MDS) system was invented. This system is extremely powerful as it uses a combination of the highly accurate GPS technique and another technique better known as multilateration. Even though multilateration is not as accurate as the GPS technique with the positioning accuracy of between 5 to 10 meters, its efficiency as a secondary airport surveillance technique cannot be wished away. The MDS system has at least three remote sensor units (RUs) which are positioned around an airport surface to identify certain emissions of radio frequencies (RF) from taxiing, landing, and taking-off aircraft. Every aircraft that operates on or closer to an airport surface are outfitted with a transponder unit capable of sending out a radio frequency signal once every second designated at a frequency of 1090Mega Hertz. The signals are usually encoded as Automatic Dependent Surveillance Broadcast (ADS-B) messages (Keller, 2003). .
The ADS-B is a more recent format of aviation positional data encoding and transmission which ensures aircrafts regularly transmits their locations directly to any other aircrafts in the surrounding. The messages have data on the latitude and longitude of the aircraft which is gotten from the GPS unit, and also the velocity and the altitude of the aircraft. Each RU receive these signals, decoding and time-stamping them with a value known as a time-of-reception value which is enabled by an in-built clock that is matched all RUs found in the system. Each RU then has to attach the time stamp value at the last part of the decoded message, and return the transmissions back to a central target processor (TP) which is normally found in the ATC tower in close proximity. In this manner, MDS system is credited for providing a highly accurate GPS solution based on a target aircraft. It also gets the crucial information that is required for independent triangulation of the aircrafts position by the use of multilateration. Multilateration can be described as a positioning technique that utilizes a mathematical concept referred to as Time Difference of Arrival (TDOA) in estimating the location of a target (Keller, 2003).
Another surveillance system that has been adopted uses the inductive loop technology. There are several problems associated with the existing radar based and GPS solutions discussed above. The two main problems of the latter are identified as disruptions in the accuracy because of RF signal reflections off the large structures, and the impediment to the capability of ATC personnel to scan the whole of the airport surface visually and track down any taxiing aircraft. It is due to these shortcomings that the inductive loop technology system were invented and used in some of the airports across the world. The LOT system also known as the inductive loop sensor subsystem is a typical example of the inductive loop system that consists of a sensor, a loop detection component, and a classification and a tracking element. According to Edward, there are four 135 by 10 inductive loops which are located beneath the airport surface in rectangular-shaped saw cuts providing the sensing component of the system. Every loop has three turns of encapsulated and trapped wires which are situated underneath the runway in a groove of about 1.5 deep and 0.25 wide. The loops are subsequently enclosed with a backer rod and finally the groove is closed with epoxy (Keller, 2003).
The loop detection component (LDC) is placed within a controller cabinet, which in most cases is to be found within 500 to 1000 ft. from the loop. A lead-in wire joins the LDC with every loop. In the event that an aircraft or a vehicle passes over the loop, an inductance variation takes place within the loop, creating a shape-based signal that is uniquely different from the various aircrafts. As the varying inductance signal goes beyond the loop detector threshold value, the LDC responds by declaring target detection. The LDC relays this time varying signal to a Classification and Tracking Component (CTC) server computer over an RS-232 interface using a spread spectrum RF communication connection. The CTC then goes ahead and identifies the target basing on the detections of the inductive signals. With the aid of the various target-tracking algorithms, the CTC continues to display the movements of the target on the output display screen when it passes above the subsequent inductive loops, integrating the tracking results from other sensor input systems (such as radar units, MDS systems, etc) to display a high accurate tracking of the aircraft (Keller, 2003, Para 20). Thus LOT can be credited for the provision of full runway tracking coverage when the units are fitted all around the airport surface (Keller, 2003).
Many runway incursions are believed to occur because of inadequate tracking coverage of airport surface, but still they can occur because of erroneous location and approach data when an aircraft attempts to touch down on a runway. To address this problem, the Local Area Augmentation System (LAAS) has been advanced. This is a different GPS- based (DGPS) precision approach and landing system consisting of three subsystems a GPS satellite, a grounded subsystem with reference antennas placed around the airport runway surface, and a data processing subsystem onboard the aircraft (Keller, 2003 Para 23). According to Keller, the GPS receivers in the aircraft and the reference antennas are designed to use a cluster of the GPS satellites in pinpointing their own locations. The data on the location which is determined by the antennas found in the grounded subsystem is put to analysis by a computerized system in order to get a discrepancy correlation and reliable data on the subsequent runway approach that is to be allocated to the aircraft. All this is relayed back to the processing subsystem that is inbuilt in the aircraft via a means of Very High Frequency (VHF) Data Broadcast apparatus. Upon receiving this differential correlation and reliable data, the processing subsystem uses the data in combination with its position information that is gotten directly from the GPS system so as to differentially calculate refined location estimates of the runway approach. This technique greatly reduces the possibility for inaccurate location and approach data with the landing aircraft having more runway approach commands in precision (Keller, 2003).
All the other systems discussed above aid in preventing incursions. However, it usually takes long before an action is taken by the ATC personnel and therefore the PathProx system has been advanced to address this problem. PathProx refers to an onboard surveillance system that is modeled to recognize early conditions that are potential for runway incursions, providing pilots and ground automobile operators with enough time to avoid incursions. This system uses data broadcasts on air traffic positioning courtesy of the Traffic Information Service-Broadcast system (TIS-B) or the Automatic Dependant Surveillance-Broadcast system (ADS-B) which obtains the traffic information from exterior surveillance sources. The PathProx system is so complex that it can handle forty different runway incursion incidents at a given time (Keller, 2003). As technology improves, so does our preventive measures on incursion at the runway. The most recent runway incursion preventive technology has been adopted in Alaska and is referred to as the Runway Awareness and Advisory System (RAAS). The system is essentially a ground proximity warning system that uses satellite technology to precisely determine the aircrafts actual position on the apron and taxiways. It also alerts the crew regarding a potential collision with other aircrafts or ground automobiles. It also provides the pilots with a moving map cock pit display showing local terrain (Broadbent, 2008, Para6). This technology was developed by Honeywell and is thought to have offered a major breakthrough in incursion prevention (Broadbent, 2008).
Runway incursions have posed a significant problem in airports across the world. However, this challenge has been handled accordingly with some achievements being noticed. However, it is important to note that all the prevention systems discussed above have failed to some extent in precision and continuous aircraft tracking. This can be positively taken to encourage research activities that might result into what has continued to be seen as ideal. As we have noted, advances in technology seems to be improving the situation bit by bit. It is my hope that the continuous improvement will finally take us to a position where by runway safety will no longer preoccupy the minds of ATC personnel and the aircraft pilots.
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