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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
all phases of flight including complex departures and
arrivals, not all systems have the same capabilities.
RNAV equipment installed in some aircraft is limited
to direct route point-to-point navigation. Therefore, it
is very important for pilots to familiarize themselves
with the capabilities of their systems through review
of the manufacturer documentation.
Most modern RNAV systems are contained within
an integrated avionics system that receives input
from several different navigation and aircraft system
sensors. These integrated systems provide so much
information that pilots may sometimes fail to recognize
errors in navigation caused by database discrepancies
or misuse. Pilots must constantly ensure that the data
they enter into their avionics is accurate and current.
Once the transition to RNAV is made during a flight,
pilots and flight crews must always be capable and
ready to revert to conventional means of navigation if
problems arise.
STORAGE LIMITATIONS
As the data in a worldwide database grows more
detailed, the required data storage space increases.
Over the years that panel-mounted GPS and FMS have
developed, the size of the commercially available airborne navigation databases has grown exponentially.
Some manufacturer’s systems have kept up with this
growth and some have not. Many of the limitations of
older RNAV systems are a direct result of limited data
storage capacity. For this reason, avionics manufacturers must make decisions regarding which types of data
records will be extracted from the master database to
be included with their system. For instance, older GPS
units rarely include all of the waypoints that are coded
into master databases. Even some modern FMSs,
which typically have much larger storage capacity, do
not include all of the data that is available from the
database producers. The manufacturers often choose
not to include certain types of data that they think is of
low importance to the usability of the unit. For example, manufacturers of FMSs used in large airplanes may
elect not to include airports where the longest runway
is less than 3,000 feet or to include all the procedures
for an airport.
Manufacturers of RNAV equipment can reduce the size
of the data storage required in their avionics by limiting
the geographic area the database covers. Like paper
charts, the amount of data that needs to be carried with
the aircraft is directly related to the size of the coverage
area. Depending on the data storage that is available,
this means that the larger the required coverage area,
the less detailed the database can be.
Again, due to the wide range of possible storage capacities, and the number of different manufacturers and
product lines, the manufacturer’s documentation is the
pilot’s best source of information regarding limitations
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Instrument Procedures Handbook (IPH)仪表程序手册下(167)
