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5-17
AREA NAVIGATION COURSES
RNAV (GPS) approach procedures introduce their own
tracking issues because they are flown using an
onboard navigation database. They may be flown as
coupled approaches or flown manually. In either case,
navigation system coding is based on procedure design,
including waypoint (WP) sequencing for an approach
and missed approach. The procedure design will indicate whether the WP is a fly-over or fly-by, and will
provide appropriate guidance for each. A fly-by (FB)
waypoint requires the use of turn anticipation to avoid
overshooting the next flight segment. A fly-over (FO)
waypoint precludes any turn until the waypoint is overflown, and is followed by either an intercept maneuver
of the next flight segment or direct flight to the next
waypoint.
Approach waypoints, except for the missed approach
waypoint (MAWP) and the missed approach holding
waypoint (MAHWP), are normally fly-by waypoints.
Notice that in the planview for figure 5-13 there are five
fly-by waypoints, but only the circled waypoint symbols at RWY 13 and SMITS are fly-over waypoints. If
flying manually to a selected RNAV waypoint, pilots
should anticipate the turn at a fly-by waypoint to ensure
a smooth transition and avoid overshooting the next
flight segment. Alternatively, for a fly-over waypoint,
no turn is accomplished until the aircraft passes the
waypoint.
There are circumstances when a waypoint may be
coded into the database as both a FB WP and a FO WP,
depending on how the waypoints are sequenced during
the approach procedure. For example, a waypoint that
serves as an IAF may be coded as a FB WP for the
approach and as a FO WP when it also serves as the
MAHWP for the missed approach procedure.
ALTITUDES
Prescribed altitudes may be depicted in four different
configurations: minimum, maximum, recommended,
and mandatory. The U.S. Government distributes
Figure 5-13. Fly-over and Fly-by Waypoints.
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approach charts produced by the National Geospatial-
Intelligence Agency (NGA) and NACO. Altitudes are
depicted on these charts in the profile view with underscore, overscore, or both to identify them as minimum,
maximum, or mandatory, respectively.
• Minimum altitudes are depicted with the altitude
value underscored. Aircraft are required to maintain altitude at or above the depicted value.
• Maximum altitudes are depicted with the altitude
value overscored. Aircraft are required to maintain altitude at or below the depicted value.
• Mandatory altitudes are depicted with the altitude
value both underscored and overscored. Aircraft
are required to maintain altitude at the depicted
value.
• Recommended altitudes are depicted without an
underscore or overscore.
NOTE: The underscore and overscore used to
identify mandatory altitudes and overscore to
identify maximum altitudes are used almost
exclusively by the NGA for military charts.
Pilots are cautioned to adhere to altitudes as prescribed because, in certain instances, they may
be used as the basis for vertical separation of
aircraft by ATC. When a depicted altitude is
specified in the ATC clearance, that altitude
becomes mandatory as defined above.
MINIMUM SAFE ALTITUDE
Minimum safe altitudes (MSAs) are published for
emergency use on IAP charts. For conventional navigation systems, the MSA is normally based on the
primary omnidirectional facility on which the IAP is
predicated. The MSA depiction on the approach chart
contains the facility identifier of the NAVAID used to
determine the MSA. For RNAV approaches, the MSA is
based on either the runway waypoint (RWY WP) or the
missed approach waypoint (MAWP) for straight-in
approaches, or the airport waypoint (APT WP) for circling only approaches. For RNAV (GPS) approaches
with a terminal arrival area (TAA) the MSA is based on
the IAF waypoint.
MSAs are expressed in feet above MSL and normally
have a 25 NM radius. This radius may be expanded to
30 NM if necessary to encompass the airport landing
surfaces. Ideally, a single sector altitude is established
and depicted on the planview of approach charts. When
necessary to maintain clearance from obstructions, the
area may be further sectored and as many as four MSAs
established. When established, sectors may be no less
than 90°in spread. MSAs provide 1,000 feet clearance
over all obstructions but do not necessarily assure
acceptable navigation signal coverage.
FINAL APPROACH FIX ALTITUDE
Another important altitude that should be briefed
during an IAP briefing is the FAF altitude, designated
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Instrument Procedures Handbook (IPH)仪表程序手册下(110)
