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sensors to compute aircraft position. Instrument
approach charts and RNAV databases needed to change
to reflect these issues. A complete discussion of airborne navigation databases is included in Appendix A
— Airborne Navigation Databases.
Due to the multi-faceted nature of RNAV, new
approach criteria have been developed to accommodate the design of RNAV instrument approaches.
This includes criteria for TAAs, RNAV basic
approach criteria, and specific final approach criteria
for different types of RNAV approaches.
TERMINAL ARRIVAL AREAS
TAAs are the method by which aircraft are transitioned
from the RNAV en route structure to the terminal area
with minimal ATC interaction. Terminal arrival areas
are depicted in the planview of the approach chart, and
each waypoint associated with them is also provided
with a unique five character, pronounceable name. The
TAA consists of a designated volume of airspace
designed to allow aircraft to enter a protected area,
offering guaranteed obstacle clearance where the initial
approach course is intercepted based on the location of
the aircraft relative to the airport. Where possible,
TAAs are developed as a basic “T” shape that is divided
into three separate arrival areas around the head of the
“T”: left base, right base, and straight-in. Typically, the
TAA offers an IAF at each of these three arrival areas
that are 3-6 NM from an IF, which often doubles as the
IAF for straight-in approaches, a FAF located approximately 5 NM from the runway threshold, and a MAP.
[Figure 5-33 on page 5-46]
Figure 5-32. Charted Visual Flight Procedures.
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Procedurally, pilots may be cleared to an IAF associated with the TAA. ATC expects the flight to proceed to
the IAF and maintain the altitude depicted for that area
of the TAA, unless cleared otherwise. An obstacle
clearance of at least 1,000 feet is guaranteed within the
boundaries of the TAA.
TAAs are modified or even eliminated if necessary to
meet the requirements of a specific airport and surrounding terrain, or airspace considerations negating
the use of the “T” approach design concept. Alternative
designs are addressed in FAA Order 8260.45A,
Terminal Arrival Area (TAA) Design Criteria.
Variations may eliminate one or both base areas, and/or
limit or modify the angular size of the straight-in area.
When both base areas are eliminated, TAAs are not
depicted in the planview. Normally, a portion of the
TAA underlies an airway. If this is not the case, at least
one feeder route is provided from an airway fix or
NAVAID to the TAA boundary. The feeder route provides a direct course from the en route fix/NAVAID to
the appropriate IF/IAF. Multiple feeder routes may also
be established. In some cases, TAAs may not be
depicted because of airspace congestion or other
operational requirements. [Figure 5-34]
RNAV FINAL APPROACH DESIGN CRITERIA
RNAV encompasses a variety of underlying navigation
systems and, therefore, approach criteria. This results
in different sets of criteria for the final approach segment of various RNAV approaches. RNAV instrument
approach criteria address the following procedures:
• GPS overlay of pre-existing nonprecision
approaches.
• VOR/DME based RNAV approaches.
• Stand-alone RNAV (GPS) approaches.
• RNAV (GPS) approaches with vertical guidance
(APV).
• RNAV (GPS) precision approaches (WAAS and
LAAS).
Figure 5-33. Terminal Arrival Area Design (Basic “T”).
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Figure 5-34. RNAV Approaches with and without TAAs.
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GPS OVERLAY OF NONPRECISION APPROACH
The original GPS approach procedures provided
authorization to fly nonprecision approaches based on
conventional, ground-based NAVAIDs. Many of these
approaches have been converted to stand-alone
approaches, and the few that remain are identified by
the name of the procedure and “or GPS.” These GPS
nonprecision approaches are predicated upon the
design criteria of the ground-based NAVAID used as
the basis of the approach. As such, they do not adhere
to the RNAV design criteria for stand-alone GPS
approaches, and are not considered part of the RNAV
(GPS) approach classification for determining design
criteria. [Figure 5-35]
GPS STAND-ALONE/RNAV (GPS) APPROACH
RNAV (GPS) approaches are named so that airborne
navigation databases can use either GPS or RNAV as
the title of the approach. This is required for non-GPS
approach systems such as VOR/DME based RNAV
systems. In the past, these approaches were often
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Instrument Procedures Handbook (IPH)仪表程序手册上(134)
