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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
caused by storage capacity of RNAV avionics.
PATH/TERMINATOR LIMITATIONS
How a specific RNAV system deals with Path/Terminators
is of great importance to pilots operating with airborne
navigation databases. Some early RNAV systems may
ignore this field completely. The ILS/DME RWY 2
approach at Durango, Colorado, provides an example of
problems that may arise from the lack of Path/Terminator
capability in RNAV systems. Although approaches of this
type are authorized only for sufficiently equipped RNAV
systems, it is possible that a pilot may elect to fly the
approach with conventional navigation, and then reengage RNAV during a missed approach. If this missed
approach is flown using an RNAV system that does not
use Path/Terminator values, then the system will most
likely ignore the first two legs of the procedure. This will
cause the RNAV equipment to direct the pilot to make an
immediate turn toward the Durango VOR instead of flying the series of headings that terminate at specific altitudes as dictated by the approach procedure. [Figure
A-10] Pilots must be aware of their individual systems
Path/Terminator handling characteristics and always
review the manufacturer’s documentation to familiarize
themselves with the capabilities of the RNAV equipment
they are operating.
Pilots should be aware that some RNAV equipment was
designed without the fly-over capability that was discussed earlier in this appendix. This can cause
problems for pilots attempting to use this equipment to fly complex flight paths in the departure,
arrival, or approach environments.
CHARTING/DATABASE INCONSISTENCIES
It is important for pilots to remember that many inconsistencies may exist between aeronautical charts and
airborne navigation databases. Since there are so many
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Instrument Procedures Handbook (IPH)仪表程序手册上(172)
