Abstract
Air transportation has become a significant mode of transportation since the last century. It enabled quick and efficient transportation of people and cargo to worldwide destinations. The growth of air transportation led to the growth of the aviation industry. A host of companies provided hardware and other requirements for practically every aspect of aviation. Navigation instruments manufacturers provided navigation instruments whose primary goal was to ensure successful arrival and departure from a location. Owing to the catastrophic nature of air accidents, air safety became, and still is, a paramount concern to aviators and their customers. This research paper discusses the development of modern navigational equipment and related systems and their contribution to aviation safety. In this paper it is argued that tremendous technological advancements, both in computing and aviation engineering have immensely contributed to greater accuracy, efficiency, cost effectiveness and safety in air transportation.
Introduction
Air Navigation involves ensuring successful movement from one place to another over a long distance by an aircraft. It involves selecting the appropriate air route and maintaining movement along it. This directional movement can be affected by factors such as wind, magnetic property of the earth or poor weather. Since time immemorial man has moved from place to place to carry out trade, launch warfare, or discover distant lands. Ancient navigator relied on stars in addition to simple instruments such as sextant and compass to navigate land and large water masses. These instruments were prone to many errors and missing the exact destination or perishing under poor weather were a common mishaps. The turn of the 20th century witnessed the emergence of air transportation on a scale never seen before. The Wright brothers ushered an era of air transportation that was faster compared to any other known means. Both people and cargo could be transported over very long distance in a relatively short period of time using an array of aircrafts.
Air navigation has seen notable changes over the year. This has been due to technological improvements on existing equipment and the need to improve air safety. Improved safety has been achieved through use of navigation aids that ensure better accuracy in estimation of direction, speed, location and distance of the aircraft from its destinations in addition to landing safety, increased pilot awareness and minimization of mid- air collision. In early day of aircraft pilots would rely on landmarks to stay on course. These include railways, rivers, bridges and highways. These landmarks were used together with a pre-drawn navigation maps. Piloting would later be supplemented with dead reckoning, a method based solely on time, distance and direction that required good experience for successful navigation and relied on the magnetic compass to keep the flying course. Later, radio communication was adopted. This involved using ground-based facilities to transmit signal at varying frequencies. The aircrafts were fitted with receiver antenna that were used to identify the frequency or Morse code and hence the position of the transmitter relative to the aircraft (Groves 2008). This equipment was called navigation aid (NAVAID(S)). Successful navigation during this period was a highly regarded feat taking for instance May 1927 Charles Lindbergh’s 3610 miles flight from New York to Paris in just 33 hours. Lindbergh’s successfully solo-navigated the Atlantic with only a compass and no other tool to account for wind or landmarks (Brain).This feat earned him worldwide acclamation. His counterpart, Emelia Earhart was not so successful. On July 2, 1937, Earhart, already with many aviation feats to her name, took off with her co-pilot for the Howland Island but their whereabouts and that of her plane to date remain shrouded in mystery. Modern analyst claim poor knowledge of radio navigation and wrong radio frequencies (she left behind important lower-frequency reception and transmission equipment) contributed to her unsuccessful journey (Naval History & Heritage Command, 2002).
Traditional navigational Systems
There has been massive improvement in navigation system since the 1920s that have been accompanied by decreased cost, size, mass and power consumption (Groves 2008). The late 1920s saw the introduction of radio transmission that greatly simplified air navigation. Radio navigation involved the use of ground based station and onboard equipment to determine the current location and distance during flight. This method of navigation lasted for better part of last century and is still in use today. Today, navigation has been greatly enhanced by inclusion of satellite communication that offers even much better precision in terms of location, distance, timing and safety. Computer and microprocessor technology has resulted in most operations of navigation being fully automated to the extent that the navigator has been relegated to a mere spectator.
Traditional aircraft navigation equipment include the Automatic Direction Finder (ADF), Very High Frequency Omnidirectional Radio Range (VOR) and Distance Measuring Equipment (DME). These systems either worked alone or were combined to a suite that served various purposes. VOR is common to most aircraft and is still in use today. It was introduced in the mid 1950s. It operates at VHF of 108.0 – 119.95 MHz. This system is made up of a ground based station and a receiver on the aircraft. The ground station transmits two signals, one omni directional and another rotational about the station. These two are interpreted by the airborne receiver and used in determining the magnetic bearing of the aircraft from the ground station (Wood 2008). Because of the relatively high frequency range, VOR offers high quality reception and suffers little interference from atmospheric noise (Aeronautical Learning Laboratory for Science, Technology & Research, 2008). Although VOR gives high accuracy, its reception can be affected by terrain surrounding the ground station, the height of the VOR beacon, the altitude of the aircraft and the distance from the ground station (Aeronautical Learning Laboratory for Science, Technology & Research 2008). In addition, reception is only possible at the “line of sight” of the ground stations (Aeronautical Learning Laboratory for Science, Technology & Research, 2008).
Navigation aid with widespread for the better part of early last century is the Automatic Direction finder (ADF). This is used together with the Non-Directional Beacon (NDB) that transmits signal in all directions. The ADF, found in the aircraft is made up of two aerial which are used for reception and in determining the position of the aircraft in relation to the magnetic north, selected ground beacons and the course. For long distance tracking such as over oceanic waters, NDB with stronger and longer range are required. Short-ranged NDBs, are however sufficient for short routes. NDB/ADF, although capable of high accuracy, suffer from a number of effects which can reduce its accuracy. This includes thunderstorms and interference from similar frequencies. Mountain and coastal areas also affect the NDB signal by reflection and refraction mechanisms respectively (Aeronautical Learning Laboratory for Science, Technology & Research, 2008). The rise of GPS has rendered many NDB/ADF navigation obsolete although some have been retained as data links to Differential GNSS (Groves 2008, p.11)
Developed in 1948, Distance measuring equipment (DME) is a navigation aid that works in conjunction with VOR at UHF to determine the distance between the aircraft and the VOR station. It is also capable of determining the ground speed and the time in relation to ground station when in “line of sight” of transmission. Together with ADF and VOR they enhance a safe approach to airfields (Tooley & Wyatt, 2008).
Modern navigation systems
Instrument Landing System (ILS) is radio navigation aid that uses both UHF and VHF and installed in airfields to enhance safe landing. It is highly accurate and can be relied upon in landing under IFR conditions (Aeronautical Learning Laboratory for Science, Technology & Research, 2008). ILS is made up of the localizer transmitter, the glide path transmitter, outer markers and approach lighting system. It provides both lateral and vertical precision approach to the airfields greatly enhancing safe landing. The localizer is a VHF transmitter with antenna that provides lateral guidance to the approaching aircraft. The glide slope equipment transmitter provides vertical guidance while the marker provides the distance of the aircraft from the runway. The lighting system forms a crucial component of ILS in providing visual aid to the pilot during landing. The lighting system include: Approach lighting system (ALS), Sequenced Flashing Light (SFL), Touch down zone light (TDZ) and Centerline light (ALLSTAR, 2008).
Area navigation (RNAV) is a method of navigation made up of a number of equipment that may include VOR/DME, LORAN, GPS and INS (FAA, 2008, 7-19). RNAV is capable of providing the pilot with information related to aircraft position, track and ground speed (FAA, 2008, 7-19).It enables the pilot locate waypoints in the “line of sight” of ground navigation aids such as VOR and DME and to fly on a specific RNAV route.
LORAN belongs to a group of long-range radio navigation systems introduced in 1940s for navigating over larges water masses and uninhabited expanses on land. Other systems in the same group as LORAN are Decca and Omega, although these two have since been decommissioned. LORAN is capable of providing highly accurate bearing, distance, time to a waypoint and also the ground speed. It can also be used in locating nearest airports during emergencies in addition to vertical navigation (FAA 2008, pg. 7-26). Despite it high accuracy, errors may result from external interference and large separation distance from ground stations. It also may also suffer from accuracy discrepancies at different times of day and night. Nevertheless it gives better accuracy than VOR systems (FAA, 2008, pg. 7-16).
Inertial Navigation System (INS) is a modern technology that is made up of computerized motion and rotation sensors that can be used to determine the position, orientation, duration and speed of flight. The main components of INS are accelerometer to measure acceleration and gyroscope for measuring direction. Documented INS errors arise as a result of change of position due to time. INS determines position based on the initial position and further positional inputs from accelerometer and gyroscope inputs. When coupled with GPS these errors are considerably reduced.
Microwave Landing System (MLS) another modern technology was introduced in 1970s to replace ILS in precision approach operations. It offers many advantages over ILS such as low setting up and maintenance cost and little interference from weather. In addition it is also able to offer precision landing in space constrained situations such as rooftop heliports (Aeronautical Learning Laboratory for Science, Technology & Research, 2008). The spread of MLS was hindered by emergence of GNSS-based navigation.
Another modern navigational system of significant mention is radar navigation. This involves transmitting a signal that on hitting an obstacle produces an echo which is used to determine the distance and bearing of that target. Radar technology however, is only able to detect objects within it range. Air Traffic Controllers (ATC) may employ radars to view aircrafts, navigational aids, and dangerous terrain features in the surrounding of an airport (FAA 2008, p.7-50). When coupled with a video-mapping unit it is possible to generate high quality maps of airways and airports that give the ATC greater monitoring and control capabilities. Radar systems used by Air Traffic Controllers include: Air Route Surveillance Radar (ARSR), Airport Surveillance Radar (ASR), Precision Approach Radar (PAR) and Airport Surface Detection Equipment (ASDE). The drawback of radar navigation is that it is not able to detect aircraft outside the coverage area of the radar or those blocked by relief such a mountains. In addition, reflective targets of small size can go undetected.
Since 1980 there has been a marked shift in navigation aid systems. Traditional ground based systems that relied on radio transmission are gradually being decommissioned in favor of satellite-based systems. These new systems offer a number of advantages over their traditional counterpart in that they are cheap to maintain, offer direct flight routes and have proved much better in navigating oceans and mountainous regions.
Global Navigation Satellite System (GNSS) has been the forerunner in the satellite-based navigation examples of which include Global Positioning System (GPS), Russian GPS (GLONASS) and the European Galileo.
GPS was developed by United States department of defense in 1992 and currently utilizes a constellation of 30 satellites (FAA 2008 p.7-33). GPS is made up of three components: the receiver, space satellites and terrestrial monitoring and control stations.GPS is capable of providing extremely accurate position and timing details. It has a global coverage and although initially confined to the military, it has now been extended to civilian aviation especially in navigating oceans and remote areas. GPS is set to completely replace traditional navigation aid through Differential Global Positioning Systems such as Wide Area Augmentation System (WAAS) and Local Area Augmentation System (LAAS). WAAS is able to cover a much wider area compared to traditional ground-based navigation aids while LAAS incorporates GPS in airfield approach operations and is limited to airport surroundings.
The popularity and widespread adoption GPS is due to many of its advantages over traditional navigation aids. GPS has enabled shorter direct flight routes that greatly save on fuel costs. It has enabled continuous, reliable and accurate positioning and monitoring of critical aspects of flight at a much reduced cost compared to expensive legacy systems (National Coordination Office for Space-Based Positioning, navigation and Timing (NCOSPVT) 2011). The technology has improved safety in aviation due to increased situational awareness it offer to pilots (NCOSPVT 2011). GPS also forms a major component of safety systems such as Enhanced Ground Proximity Warning System (EGPWS) that are used to navigate terrains.
The high number of flight instrument both on board and on land necessitated the need to organize and harmonize their operation. Flight Management Systems was specifically created for this purpose. This system is able to presents data such as position, track, desired heading, ground speed and position relative to desired track (FAA 2008, p. 7-48).FMS works by receiving data from navigational aids such as VOR and DME. It also makes it possible for pilots to define flight route, manage fuel and control other navigational aids in the aircraft or on ground. FMS normally are linked to a database of Airports Locations, navigational aids, aircraft data, airways and intersections which can be used to set the travel route during or before flight (FAA 2008, , p. 7-48).
Improvement in aviation engineering and allied technologies has given rise to sophisticated and fully automated aviation system. Because air accidents have zero-survival rate government and companies have always been under obligation to develop safety technologies to minimize such accidents. These efforts have contributed to increased air safety over the years. Some of these systems are discussed in the following sections.
Safety Systems
These are systems designed specifically for safety of the air travelers during flight. Their primary goal is to greatly minimize air accidents although it is important to point out some air catastrophes still occur despite the aircraft having the most sophisticated safety and navigation systems. Some of these systems are Radio Altimeters, Traffic Advisory Systems, Traffic Avoidance Systems and Terrain Alerting System. Radio altimeter provides the height above the terrain directly beneath the aircraft (FAA, 2008, p.3-30). It provides crucial altitude information to the pilot during approach and landing.
Traffic Advisory Systems such as the terrestrial TIS (Traffic Information Service) avails the pilot with information about nearby traffic enabling to make safety decisions in time. This information is relayed on board via a data link that uses S-mode transponder and an altitude encoder (FAA, 2008, p. 3-31).
Traffic Alert System enhances air safety by alerting the pilot about other aircrafts that may be dangerously flying close by. The system is able to compute the position of intruder aircrafts enabling the pilot act accordingly.
Mid air collision is probably the most catastrophic air accidents that can occur. High air traffic due to the high growth of air transportation means that their always is a possibility of such accidents occurring.The nature of air accident is such that they have zero-survival rate as illustrated by the two cases below:
On the night of July 1, 2002 a Boeing B-757 cargo transporter DHL collided with a Russian Tu-154 passenger jet at 34,940 ft over Germany killing all 71 crew members and passengers aboard the two planes. In another similar catastrophe, a Boeing 737 and Embraer Legacy 600 business jet collided over the Amazon jungle in September 2006 killing all on board (Kuchar & Druman, 2007, p.283).
Traffic Avoidance Systems such as the Traffic Alert and Collision Avoidance System (TCAS) were created in order to limit the occurrence of such cases. TCAS is made up special sensors that gather data about the intruder aircraft such as relative position and velocity which are then computed by on-board systems to determine the level of threat ( Kuchar & Druman, 2007, p.279). This data may also be relayed to the intruder aircraft in case it is fitted with TCAS so that pilots of the two aircraft can undertake safe maneuvers out of the situation. In case the intruder aircraft presents real danger to the incoming aircraft, the system is able to offer advisory response (Kuchar & Druman, 2007, p. 279). TCAS only act as advisory aids to the pilot. It is up to the pilots of the two planes to act fast to avoid a mid-air collision. Investigators of the DHL-Russian Tu-154 collision attributed the cause of the accident to the ignoring of TCAS warnings by the Russian pilots (Kuchar & Druman, 2007, p. 283). Both aircrafts had been fitted with TCAS.
Many air crashes have occurred in terrain. The 1995American Airline Flight 965 crash in Cali, Columbia remains one of the most catastrophic air accidents in which 159 crew and passengers lost their lives. Investigators later classified it as a Controlled Flight into Terrain (CFIT) accident caused mainly by “pilot error” (Wikipedia, 2011). To contain this accident a number of systems have been developed. Ground Proximity Warning System (GPWS) is a terrain alerting system that determines the aircraft height above ground level. It uses radio altimeter, speed and barometric altitude to determine the aircraft position relative to rising terrain (FAA 2008,. p. 3-31). However, this system in ineffective in mountainous areas due to unusual slopes that give unpredictive information (FAA 2008, Pg 3-31). Another terrain alerting system, Terrain Awareness and warning system (TAWS) uses GPS and a database of terrains to provide predictability of upcoming terrains and obstacles during flight ((FAA 2008, Pg 3-31). Many modern aircrafts also feature Head-Up Display (HUD) that improves the pilot concentration and situational awareness by providing a projection of important data such as speed and altitude on the windshield thus diminishing the need for the pilot to physically observe the outside of the aircraft during flight.
Conclusion
Air navigation has undergone tremendous changes since the early days of air transportation from manual piloting, dead reckoning, radio navigation to fully automated satellite-based systems. Improvements in technology have perfected the art of landing, take off, maneuvering, direction and position finding.
Air accidents are accidents like no other. Very few people survive air accidents. Such accidents may occur as a result of air head-on collision, poor visibility due to inclement weather or pilot error. It is common for the pilot to “get lost” and crash on running out of fuel. Improved computer technology together with superior aviation engineering has give rise to fully automated navigation and safety systems. The combination of both navigation and safety systems has enabled safe passage of aircrafts over dangerous terrestrial features such mountains.
New cost effective satellite-based systems are quickly replacing a multitude of traditional navigation aids. These systems have made it possible to successfully land and take off from practically every corner of the corner. Superior navigation and safety systems such as GPS have transformed aviation form a local to an international affair. Today, it is possible to map direct flight routes that are cheaper in fuel and fares. Traditional navigation aids have a high deployment and maintenance cost. In addition they provide a steep learning curve to learner as many instruments from different vendors have to be mastered. However, there has been tendency to over depend on satellite systems at the expense of viable legacy systems and equipment. This is despite the fact that such systems are operated at the will of countries which own them. It is important that some effective and reliable legacy systems be retained to provide backup in case of a satellite outage. Superior navigation and safety systems have not completely prevented aircraft accidents from occurring. In this respect it is important to increase the human-pilot capacity to effectively control an aircraft. This is because human input will still be required to complement machine input no matter how sophisticated our current technologies become.
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