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.
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.
- Localizer Back Course Approach.
- Localizer-type Directional Aid (LDA).