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associated glide slope is typically no less than 2 degrees
Figure 5-52. St. Mary’s (PASM), St. Mary’s, Alaska, NDB DME RWY 16.
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and no more than 3 degrees. Obstacle clearance for the
final approach area is based on the particular established glide slope angle and the exact formula is outlined in TERPS Volume 1, Chapter 10. [Figure 5-54]
AIRPORT SURVEILLANCE RADAR
ASR approaches are typically only approved when
necessitated for an ATC operational requirement, or in
an unusual or emergency situation. This type of radar
only provides heading and range information, although
the controller can advise the pilot of the altitude where
the aircraft should be based on the distance from the
runway. An ASR approach procedure can be established at any radar facility that has an antenna within
20 NM of the airport and meets the equipment
requirements outlined in Order 8200.1, U.S.
Standard Flight Inspection Manual (latest version).
ASR approaches are not authorized for use when
Center Radar ARTS processing (CENRAP) procedures are in use due to diminished radar capability.
The final approach course for an ASR approach is
aligned with the runway centerline for straight-in
approaches and aligned with the center of the airport
for circling approaches. Within the final approach area,
the pilot is also guaranteed a minimum of 250 feet
obstacle clearance. ASR descent gradients are designed
to be relatively flat, with an optimal gradient of 150 feet
per mile and never exceeding 300 feet per mile.
LOCALIZER APPROACHES
As an approach system, the localizer is an extremely
flexible approach aid that, due to its inherent design,
provides many applications for a variety of needs in
instrument flying. An ILS glide slope installation may
be impossible due to surrounding terrain. For whatever
reason, the localizer is able to provide four separate
applications from one approach system:
• Localizer Approach.
• Localizer/DME Approach.
Figure 5-53. Asheville Regional (KAVL), Asheville, NC, Radar Instrument Approach Minimums.
Obstacle Clearance Surface (OCS)
975 10,000 40,000
Glide Slope 2°– 3°
Ground Point of
Interception (GPI)
Figure 5-54. PAR Final Approach Area Criteria.
5-64
• Localizer Back Course Approach.
• Localizer-type Directional Aid (LDA).
LOCALIZER AND LOCALIZER DME
The localizer approach system can provide both
precision and nonprecision approach capabilities to
a pilot. As a part of the ILS system, the localizer
provides horizontal guidance for a precision
approach. Typically, when the localizer is discussed, it is thought of as a nonprecision approach
due to the fact that either it is the only approach
system installed, or the glide slope is out of service
on the ILS. In either case, the localizer provides a
nonprecision approach using a localizer transmitter
installed at a specific airport. [Figure 5-55]
TERPS provide the same alignment criteria for a localizer approach as it does for the ILS since it is essentially
the same approach without vertical guidance stemming
from the glide slope. A localizer is always aligned within
Figure 5-55. Vicksburg Tallulah Regional (KTVR), Tallulah/Vicksburg, Louisiana, LOC RWY 36.
5-65
3 degrees of the runway, and it is afforded a minimum of
250 feet obstacle clearance in the final approach area. In
the case of a localizer DME (LOC DME) approach, the
localizer installation has a collocated DME installation
that provides distance information required for the
approach. [Figure 5-56]
LOCALIZER BACK COURSE
In cases where an ILS is installed, a back course may
be available in conjunction with the localizer. Like
the localizer, the back course does not offer a glide
slope, but remember that the back course can project
a false glide slope signal and the glide slope should
be ignored. Reverse sensing will occur on the back
course using standard VOR equipment. With an
HSI (horizontal situation indicator) system,
reverse sensing is eliminated if it is set appropriately to the front course. [Figure 5-57 on page 5-66]
LOCALIZER-TYPE DIRECTIONAL AID
An LDA is a NAVAID that provides nonprecision
approach capabilities. The LDA is essentially a localizer. It is termed LDA because the course alignment
with the runway exceeds 3 degrees. Typically, an LDA
Figure 5-56. Davidson County (KEXX), Lexington, North Carolina, LOC DME RWY 6.
5-66
installation does not incorporate a glide slope component. However, the availability of a glide slope associated with an LDA is noted on the approach chart. This
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Instrument Procedures Handbook (IPH)仪表程序手册下(137)
