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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
referred to as stand-alone GPSs. They are considered
nonprecision approaches, offering only LNAV and
circling minimums. Precision minimums are not
authorized, although LNAV/VNAV minimums may
be published and used as long as the on-board system
is capable of providing approach approved VNAV.
The RNAV (GPS) Runway 18 approach for
Alexandria, Louisiana incorporates only LNAV and
circling minimums. [Figure 5-36]
Figure 5-35. Traditional GPS Overlay Approach.
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For a non-vertically guided straight-in RNAV (GPS)
approach, the final approach course must be aligned
within 15° of the extended runway centerline. The final
approach segment should not exceed 10 NM, and when
it exceeds 6 NM, a stepdown fix is typically incorporated. A minimum of 250 feet obstacle clearance is also
incorporated into the final approach segment for
straight-in approaches, and a maximum 400-foot per
NM descent gradient is permitted.
The approach design criteria are different for
approaches that use vertical guidance provided by a
Baro-VNAV system. Because the Baro-VNAV guidance is advisory and not primary, Baro-VNAV
approaches are not authorized in areas of hazardous ter-
rain, nor are they authorized when a remote altimeter
setting is required. Due to the inherent problems associated with barometric readings and cold temperatures,
these procedures are also temperature limited.
Additional approach design criteria for RNAV
Approach Construction Criteria can be found in the
appropriate Order 8260 series directives.
RNAV (GPS) APPROACH USING WAAS
WAAS was commissioned in July, 2003, with initial
operational capability (IOC). Although precision
approach capability is still in the future, initial WAAS
currently provides a new type of approach with vertical
guidance (APV) known as LPV. Approach minimums as
low as 200 feet HAT and 1/2 SM visibility are possible,
Figure 5-36. Alexandria International (KAEX), Alexandria, Louisiana, RNAV (GPS) RWY 18.
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even though LPV is semi-precision, and not considered
a precision approach. WAAS covers 95 percent of the
country 95 percent of the time.
NOTE: WAAS avionics receive an airworthiness
approval in accordance with Technical Standard Order
(TSO) C-145A, Airborne Navigation Sensors Using
the (GPS) Augmented by the Wide Area Augmentation
System (WAAS), or TSO-146A, Stand-Alone Airborne
Navigation Equipment Using the Global Positioning
System (GPS) Augmented by the Wide Area
Augmentation System (WAAS), and installed in
accordance with AC 20-130A, Airworthiness
Approval of Navigation or Flight Management
Systems Integrating Multiple Navigation Sensors, or
AC 20-138A, Airworthiness Approval of Global
Positioning System (GPS) Navigation Equipment for
Use as a VFR and IFR Navigation System.
Precision approach capability will become available
when LAAS becomes operational. LAAS further
increases the accuracy of GPS and improves signal
integrity warnings. Precision approach capability
　
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