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1、A-1 EVOLUTION OF AIRBORNE NAVIGATION DATABASES There are nearly as many different area navigation (RNAV) platforms operating in the National Airspace System (NAS) as there are aircraft types. The range of systems and their capabilities is greater now than at any other time in aviation history. From
2、the sim- plest panel-mounted LOng RAnge Navigation (LORAN), to the mov- ing-map display global positioning system (GPS) currently popular for general aviation aircraft, to the fully integrated flight management system (FMS) installed in corpo- rate and commercial aircraft, the one common essential e
3、lement is the database. Figure A-1 RNAV systems must not only be capable of determining an air- crafts position over the surface of the earth, but they also must be able to determine the location of other fixes in order to navigate. These systems rely on airborne navigation databases to provide deta
4、iled information about these fixed points in the airspace or on the earths surface. Although, the location of these points is the pri- mary concern for navigation, these databases can also provide many other useful pieces of information about a given location. HISTORY In 1973, National Airlines inst
5、alled the Collins ANS- 70 and AINS-70 RNAV systems in their DC-10 fleet; this marked the first commercial use of avionics that required navigation databases. A short time later, Delta Air Lines implemented the use of an ARMA Corporation RNAV system that also used a navigation database. Although the
6、type of data stored in the two sys- tems was basically identical, the designers created the databases to solve the individual problems of each sys- tem. In other words, the data was not interchangeable. This was not a problem because so few of the sys- tems were in use, but as the implementation of
7、RNAV systems expanded, a world standard for air- borne navigation databases had to be created. In 1973, Aeronautical Radio, Inc. (ARINC) sponsored the formation of a committee to standardize aeronauti- cal databases. In 1975, this committee published the first standard (ARINC Specification 424), whi
8、ch has remained the worldwide-accepted format for coding airborne navigation databases. There are many different types of RNAV systems certi- fied for instrument flight rules (IFR) use in the NAS. The two most prevalent types are GPS and the multi- sensor FMS. Figure A-1. Area Navigation Receivers.
9、A-2 Most GPSs operate as stand-alone RNAV systems. A modern GPS unit accurately provides the pilot with the aircrafts present position; however, it must use an air- borne navigation database to determine its direction or distance from another location unless a latitude and longitude for that locatio
10、n is manually entered. The database provides the GPS with position information for navigation fixes so it may perform the required geo- detic calculations to determine the appropriate tracks, headings, and distances to be flown. Modern FMSs are capable of a large number of func- tions including basi
11、c en route navigation, complex departure and arrival navigation, fuel planning, and precise vertical navigation. Unlike stand-alone naviga- tion systems, most FMSs use several navigation inputs. Typically, they formulate the aircrafts current position using a combination of conventional distance mea
12、suring equipment (DME) signals, inertial navigation systems (INS), GPS receivers, or other RNAV devices. Like stand-alone navigation avionics, they rely heavily on air- borne navigation databases to provide the information needed to perform their numerous functions. DATABASE CAPABILITIES The capabil
13、ities of airborne navigation databases depend largely on the way they are implemented by the avionics manufacturers. They can provide data about a large variety of locations, routes, and airspace segments for use by many different types of RNAV equipment. Databases can provide pilots with informatio
14、n regard- ing airports, air traffic control frequencies, runways, special use airspace, and much more. Without airborne navigation databases, RNAV would be extremely lim- ited. PRODUCTION AND DISTRIBUTION In order to understand the capabilities and limitations of airborne navigation databases, pilot
15、s should have a basic understanding of the way databases are compiled and revised by the database provider and processed by the avionics manufacturer. THE ROLE OF THE DATABASE PROVIDER Compiling and maintaining a worldwide airborne navi- gation database is a large and complex job. Within the United
16、States (U.S.),the Federal Aviation Administration (FAA) sources give the database providers information, in many different formats, which must be analyzed, edited, and processed before it can be coded into the database. In some cases, data from outside the U.S. must be translated into English so it
17、may be analyzed and entered into the database. Once the data is coded following the specifications of ARINC 424 (see ARINC 424 later in this appendix), it must be continu- ally updated and maintained. Once the FAA notifies the database provider that a change is necessary, the update process begins.1
18、The change is incorporated into a 28-day airborne database revision cycle based on its assigned priority. If the information does not reach the coding phase prior to its cutoff date (the date that new aeronautical information can no longer be included in the next update), it is held out of revision
19、until the next cycle. The cutoff date for aeronautical databases is typically 21 days prior to the effective date of the revision.2 The integrity of the data is ensured through a process called cyclic redundancy check (CRC). A CRC is an error detection algorithm capable of detecting small bit-level
20、changes in a block of data. The CRC algorithm treats a data block as a single (large) binary value. The data block is divided by a fixed binary number (called a “generator polynomial”) whose form and magnitude is determined based on the level of integrity desired. The remainder of the division is th
21、e CRC value for the data block. This value is stored and transmitted with the cor- responding data block. The integrity of the data is checked by reapplying the CRC algorithm prior to dis- tribution, and later by the avionics equipment onboard the aircraft. RELATIONSHIP BETWEEN EFB AND FMS DATABASES
22、 The advent of the Electronic Flight Bag (EFB) dis- cussed in Chapter 6 illustrates how the complexity of avionics databases is rapidly accelerating. The respec- tive FMS and EFB databases remain independent of each other even though they may share some of the same data from the database providers m
23、aster naviga- tion database. For example, FMS and GPS databases both enable the retrieval of data for the onboard aircraft navigation system. Additional data types that are not in the FMS database are extracted for the EFB database, allowing replace- ment of traditional printed instrument charts for
24、 the 1The majority of the volume of official flight navigation data in the U.S. disseminated to database providers is primarily supplied by FAA sources. It is supplemented by airport managers, state civil aviation authorities, Department of Defense (DOD) organizations such as the National Geospatial
25、-Intelligence Agency (NGA), branches of the military service, etc. Outside the U.S., the majority of official data is pro- vided by each countrys civil aviation authority, the equivalent of the FAA, and disseminated as an aeronautical information publication (AIP). 2The database provider extract occ
26、urs at the 21-day point.The edited extract is sent to the avionics manufacturer or prepared with the avionics-packing program. Data not coded by the 21-day point will not be contained in the database extract for the effective cycle. In order for the data to be in the database at this 21-day extract,
27、 the actual cutoff is more like 28 days before the effective date. A-3 pilot. The three EFB charting applications include Terminal Charts, En route Moving Map (EMM), and Airport Moving Map (AMM). The Terminal Charts EFB charting application utilizes the same information and layout as the printed cha
28、rt counterpart. The EMM application uses the same ARINC 424 en route data that is extracted for an FMS database, but adds addi- tional information associated with aeronautical charting needs. The EFB AMM database is a new high-resolution geo-spatial database only for EFB use. The AMM shows aircraft
29、proximity relative to the airport environment. Runways depicted in the AMM correlate to the runway depictions in the FMS navigation database. The other information in the AMM such as ramps, aprons, taxiways, buildings, and hold-short lines are not included in traditional ARINC 424 databases. THE ROL
30、E OF THE AVIONICS MANUFACTURER When avionics manufacturers develop a piece of equipment that requires an airborne navigation data- base, they typically form an agreement with a database provider to supply the database for that new avionics platform. It is up to the manufacturer to determine what inf
31、ormation to include in the database for their system. In some cases, the navigation data provider has to significantly reduce the number of records in the database to accommodate the storage capacity of the manufacturers new product. The manufacturer must decide how its equipment will handle the rec
32、ords; decisions must be made about each field in the record. Each manufacturer can design their systems to manipulate the data fields in different ways, depending on the needs of the avionics user. Some fields may not be used at all. For instance, the ARINC primary record designed for individual run
33、ways may or may not be included in the database for a specific manufacturers machine. The avionics manufacturer might specify that the database include only runways greater than 4,000 feet. If the record is included in the tailored database, some of the fields in that record may not be used. Another
34、 important fact to remember is that although there are standard naming conventions included in the ARINC 424 specification; each manufacturer determines how the names of fixes and procedures are displayed to the pilot. This means that although the database may specify the approach identifier field f
35、or the VOR/DME Runway 34 approach at Eugene Mahlon Sweet Airport (KEUG) in Eugene, Oregon, as “V34,” different avion- ics platforms may display the identifier in any way the manufacturer deems appropriate. For example, a GPS produced by one manufacturer might display the approach as “VOR 34,” wherea
36、s another might refer to the approach as “VOR/DME 34,” and an FMS pro- duced by another manufacturer may refer to it as “VOR34.” Figure A-2 These differences can cause visual inconsistencies between chart and GPS displays as well as confusion with approach clearances and other ATC instructions for p
37、ilots unfamiliar with spe- cific manufacturers naming conventions. The manufacturer determines the capabilities and limi- tations of an RNAV system based on the decisions that it makes regarding that systems processing of the air- borne navigation database. USERS ROLE Like paper charts, airborne nav
38、igation databases are subject to revision. Pilots using the databases are ulti- mately responsible for ensuring that the database they are operating with is current. This includes checking “NOTAM-type information” concerning errors that may be supplied by the avionics manufacturer or the database su
39、pplier. The database user is responsible for learning how the specific navigation equipment handles the navi- gation database. The manufacturers documentation is Figure A-2. Naming Conventions of Three Different Systems for the VOR 34 Approach. A-4 the pilots best source of information regarding the
40、 capa- bilities and limitations of a specific database. Figure A-3 Figure A-3. Database Roles. COMPOSITION OF AIRBORNE NAVIGATION DATABASES The concept of global position is an important concept of RNAV. Whereas short-range navigation deals prima- rily with azimuth and distance on a relatively small
41、, flat surface, long-range point-to-point navigation must have a method of defining positions on the face of a large and imperfect sphere (or more specifically a mathematical reference surface called a geodetic datum). The latitude-longitude system is currently used to define these positions. Each l
42、ocation/fix defined in an airborne navigation database is assigned latitude and longitude values in reference to a geodetic datum that can be used by avionics systems in navigation calculations. THE WGS-84 REFERENCE DATUM The idea of the earth as a sphere has existed in the sci- entific community si
43、nce the early Greeks hypothesized about the shape and size of the earth over 2,000 years ago. This idea has become scientific fact, but it has been modified over time into the current theory of the earths shape. Since modern avionics rely on databases and mathematical geodetic computations to determ
44、ine the distance and direction between points, those avionics systems must have some common frame of reference upon which to base those calculations. Unfortunately, the actual topographic shape of the earths surface is far too complex to be stored as a reference datum in the memory of todays FMS or
45、GPS data cards. Also, the mathematical calculations required to determine dis- tance and direction using a reference datum of that complexity would be prohibitive. A simplified model of the earths surface solves both of these problems for todays RNAV systems. In 1735, the French Academy of Sciences
46、sent an expedition to Peru and another to Lapland to measure the length of a meridian degree at each location. The expeditions determined conclusively that the earth is not a perfect sphere, but a flattened sphere, or what geologists call an ellipsoid of revolution. This means that the earth is flat
47、tened at the poles and bulges slightly at the equator. The most current measurements show that the polar diameter of the earth is about 7,900 statute miles and the equatorial diameter is 7,926 statute miles. This discovery proved to be very impor- tant in the field of geodetic survey because it incr
48、eased the accuracy obtained when computing long distances using an earth model of this shape. This model of the earth is referred to as the Reference Ellipsoid, and combined with other mathematical parameters, it is used to define the reference for geodetic calculations or what is referred to as the
49、 geodetic datum. Historically, each country has developed its own geo- detic reference frame. In fact, until 1998 there were more than 160 different worldwide geodetic datums. This complicated accurate navigation between loca- tions of great distance, especially if several reference datums are used along the route. In order to simplify RNAV and facilitate the use of GPS in the NAS, a com- mon reference frame has evolved. The reference datum currently being used in North America for airborne navigation databases is the North American Datum of 1983 (NAD-83), which for all