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necessitated the development of the “Path/Terminator”
field that is included in complex route records.
There are currently 23 different Path/Terminators in the
ARINC 424 standard. They enable RNAV systems to
follow the complex paths that make up instrument
departures, arrivals, and approaches. They describe to
navigation avionics a path to be followed and the criteria that must be met before the path concludes and the
next path begins. One of the simplest and most common Path/Terminators is the track to a fix (TF), which
is used to define the great circle route between two
known points. [Figure A-7] Additional information on
Path/Terminator leg types is contained in Chapter 4.
The GRAND JUNCTION FOUR DEPARTURE for
Walker Field in Grand Junction, Colorado, provides a
good example of another type of Path/Terminator.
[Figure A-8 on page A-8] When this procedure is coded
into the navigation database, the person entering the
data into the records must identify the individual legs
of the flight path and then determine which type of
terminator should be used.
The first leg of the departure for Runway 11 is a climb
via runway heading to 6,000 feet mean sea level (MSL)
and then a climbing right turn direct to a fix. When this
is entered into the database, a heading to an altitude
(VA) value must be entered into the record’s
Path/Terminator field for the first leg of the departure
route. This Path/Terminator tells the avionics to provide
course guidance based on heading, until the aircraft
reaches 6,000 feet, and then the system begins providing
course guidance for the next leg. After reaching 6,000
feet, the procedure calls for a right turn direct to the
Grand Junction (JNC) VORTAC. This leg is coded into
the database using the Path/Terminator direct to a fix
(DF) value, which defines an unspecified track starting
from an undefined position to a specific database fix.
After reaching the JNC VORTAC the only
Path/Terminator value used in the procedure is a TF leg.
Another commonly used Path/Terminator value is
heading to a radial (VR). Figure A-9 on page A-9
shows the CHANNEL ONE DEPARTURE procedure
for Santa Ana, California. The first leg of the runway
19L/R procedure requires a climb on runway heading
until crossing the I-SNA 1 DME fix or the SLI R-118,
this leg must be coded into the database using the VR
value in the Path/Terminator field. After crossing the
TF Leg
Figure A-7. Path/Terminator. A Path/Terminator value of a TF
leg indicates a great circle track directly from one fix to the next.
A-8
I-SNA 1 DME fix or the SLI R-118, the avionics
should cycle to the next leg of the procedure that in
this case, is a climb on a heading of 175° until crossing SLI R-132. This leg is also coded with a VR
Path/Terminator. The next leg of the procedure consists of a heading of 200° until intercepting the SXC
R-084. In order for the avionics to correctly process
this leg, the database record must include the heading
to an intercept (VI) value in the Path/Terminator field.
This value directs the avionics to follow a specified
heading to intercept the subsequent leg at an unspecified position.
Figure A-8. Grand Junction Four Departure.
A-9
The Path/Terminator concept is a very important part
of airborne navigation database coding. In general, it is
not necessary for pilots to have an in-depth knowledge
of the ARINC coding standards; however, pilots should
be familiar with the concepts related to coding in order
to understand the limitations of specific RNAV systems
that use databases. For a more detailed discussion of
coding standards, refer to ARINC Specification 424-15
Navigation System Data Base.
Figure A-9. Channel One Departure.
A-10
OPERATIONAL LIMITATIONS OF
AIRBORNE NAVIGATION DATABASES
Understanding the capabilities and limitations of the
navigation systems installed in an aircraft is one of the
pilot’s biggest concerns for IFR flight. Considering the
vast number of RNAV systems and pilot interfaces
available today, it is critical that pilots and flight crews
be familiar with the manufacturer’s operating manual
for each RNAV system they operate and achieve and
retain proficiency operating those systems in the IFR
environment.
RELIANCE ON NAVIGATION AUTOMATION
Most professional and general aviation pilots are
familiar with the possible human factors issues
related to cockpit automation. It is particularly
important to consider those issues when using airborne navigation databases. Although modern
avionics can provide precise guidance throughout
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Instrument Procedures Handbook (IPH)仪表程序手册上(171)
