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airways, and approaches), as well as the format in
which the data is coded. The ARINC specification
determines naming conventions.
RECORDS
The data included in an airborne navigation database is
organized into ARINC 424 records. These records are
strings of characters that make up complex descriptions
of each navigation entity. There are 132 columns or
spaces for characters in each record. Not all of the 132
character-positions are used for every record — some
of the positions are left blank to permit like information
to appear in the same columns of different records, and
others are reserved for possible future record expansion. These records are divided into fields that contain
specific pieces of information about the subject of the
record. For instance, the primary record for an airport,
such as KZXY, contains a field that describes the
longest runway at that airport. The columns 28 through
30 in the record contain the first three digits in the
longest runway’s length in feet. If the numbers 0, 6, and
5 were in the number 28, 29, and 30 columns respectively, the longest runway at KZXY would be recorded
in the record as 6,500 feet (065). [Figure A-4] Columns
28 through 30, which are designated as “longest runway” in the airport record, would be a different field in
the record for a very high frequency omni-directional
range (VOR) or an airway. The record type determines
what fields are included and how they are organized.
For the purpose of discussion, ARINC records can be
sorted into four general groups – fix records, simple
route records, complex route records, and miscellaneous records. Although it is not important for pilots to
have in-depth knowledge of all the fields contained in
the ARINC 424 records, pilots should be aware of the
types of records contained in the navigation database
and their general content.
Columns—The spaces for data entry on each record.
One column can accommodate one character.
Record—A single line of computer data made up of
the fields necessary to define fully a single useful piece
of data.
Field—The collection of characters needed to define
one item of information.
FIX RECORDS
Database records that describe specific locations on the
face of the earth can be considered fix records.
NAVAIDs, waypoints, intersections, and airports are all
examples of this type of record. These records can be
used directly by avionics systems and can be included
as parts of more complex records like airways or
approaches.
Within the 132 characters that make up a fix record,
there are several fields that are generally common to
all: record type, latitude, longitude, ICAO fix identifier,
and ICAO location code. One exception is airports that
use FAA identifiers. In addition, fix records contain
many fields that are specific to the type of fix they
describe. Figure A-5 on page A-6 shows examples of
field types for three different fix records.
In each of the above examples, magnetic variation is
dealt with in a slightly different manner. Since the locations of these fixes are used to calculate the magnetic
courses displayed in the cockpit, their records must
include the location’s magnetic variation to be used in
Airport
Primary
Record 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 8 7 6 5 4 3 2 1
0 5 7 2 3 6 0 4 1 8 3 5 2 7 9 6 4 3 1 0 8 5 2 7 4 1 9 0 6 5 8 1 3 4 7 5 9 8 0 6 7 9 3 4 1 2 5 7 0 8 6 4 5 3 9 1 7 2 0 8 4 6 5 3 9 8 1 4 7 2 3 5 0 6 8 9 4 1 5 2
27 28 29 30 31
9 0 6 5 1 8 1
3 Longest Runway 6,500 feet
Figure A-4. Longest Runway Field in an Airport Record.
A-6
those calculations. In records for airports for instance,
the magnetic variation is given as the difference in
degrees between the measured values of true north and
magnetic north at that location. The field labeled
“Station Declination” in the record for a VOR differs
only slightly in that it is the angular difference between
true north and the zero degree radial of the NAVAID
the last time the site was checked. The record for a waypoint, on the other hand, contains a field named
“Dynamic Magnetic Variation,” which is simply a
computer model calculated value instead of a measured
value.
Another concept pilots should understand relates to
how aircraft make turns over navigation fixes. Fixes
can be designated as fly-over or fly-by depending on
how they are used in a specific route. [Figure A-6]
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Instrument Procedures Handbook (IPH)仪表程序手册上(169)
