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Under certain circumstances, a navigation fix is designated as fly-over. This simply means that the aircraft
must actually pass directly over the fix before initiating
a turn to a new course. Conversely, a fix may be designated fly-by, allowing an aircraft’s navigation system
to use its turn anticipation feature, which ensures that
the proper radius of turn is commanded to avoid overshooting the new course. Some RNAV systems are not
programmed to fully use this feature. It is important to
remember a fix can be coded as fly-over in one proce-
dure, and fly-by in another, depending on how the fix
is used.
SIMPLE ROUTE RECORDS
Route records are those that describe a flight path
instead of a fixed position. Simple route records contain strings of fix records and information pertaining to
how the fixes should be used by the navigation avionics. A Victor Airway, for example, is described in the
database by a series of “en route airway records” that
contain the names of fixes in the airway and information about how those fixes make up the airway. These
records describe the way the fixes are used in the airway and contain important information including the
fix identifier, sequence number, route type, required
navigation performance (RNP), outbound and inbound
magnetic courses (if appropriate), route distance, and
minimum and maximum altitudes for the route.
Sequence number fields are a necessary addition to the
navigation database because they allow the avionics
system to track the fix order within the route. Most
routes can be entered from any point and flown in both
directions. The sequence number allows the avionics to
keep track of the fixes in order, so that the proper flight
path can be followed starting anywhere within the
route.
Fly-By
Fly-Over
Flight Plan Path
Airplane Track
Figure A-6. Fly-By and Fly-Over Waypoints.
Airport VOR Waypoint
• Longest Runway
• IFR Capability
• Magnetic Variation
• Airport Elevation
• Transition Altitude
or Flight Level
• VOR Frequency
• NAVAID Class
• Station/Declination
• DME Ident
• Waypoint Type
• Waypoint Usage
• Dynamic Magnetic Variation
Figure A-5. Unique Fields for Three Different Fix Records.
A-7
COMPLEX ROUTE RECORDS
Complex route records include those strings of fixes
that describe complex flight paths like standard instrument departures (SIDs), standard terminal arrival
routes (STARs), and instrument approach procedures.
Like simple routes, these records contain the names of
fixes to be used in the route as well as instructions on
how the route will be flown. However, there are several
fields included in these records that are unique to this
type.
SID procedures are examples of complex routes that
are coded in airborne navigation databases. The record
for a SID includes many of the same types of information that are found in the en route airway record,
and many other pieces of information that pertain
only to complex flight paths. Some examples of the
fields included in the SID record are the airport
identifier, SID identifier, transition identifier, turn
direction, recommended NAVAID, magnetic course,
and path/terminator.
MISCELLANEOUS RECORDS
There are several other types of records coded into airborne navigation databases, most of which deal with
airspace or communications. For example, there are
records for restricted airspace, airport minimum safe
altitudes, and grid minimum off route altitudes
(MORAs). These records have many individual and
unique fields that combine to describe the record’s subject. Some are used by avionics manufacturers, some
are not, depending on the individual capabilities of
each RNAV unit.
THE PATH/TERMINATOR CONCEPT
One of the most important concepts for pilots to learn
regarding the limitations of RNAV equipment has to do
with the way these systems deal with the
“Path/Terminator” field included in complex route
records.
The first RNAV systems were capable of only one type
of navigation: they could fly directly to a fix. This was
not a problem when operating in the en route environment in which airways are mostly made up of direct (or
very nearly direct) routes between fixes. The instrument approaches that were designed for RNAV also
presented no problem for these systems and the databases they used since they consisted mainly of GPS
overlay approaches that demanded only direct point-topoint navigation. The desire for RNAV equipment to
have the ability to follow more complicated flight paths
　
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