“Localizer type directional aid”的意思、由来-开放百科全书

A localizer type directional aid (LDA) is a type of localizer-based instrument approach to an airport. It is used in places where, due to terrain and other factors, the localizer antenna array is not aligned with the runway it serves. In these cases, the localizer antenna array may be offset (i.e. pointed or aimed) in such a way that the approach course it projects no longer lies along the extended runway centerline (which is the norm for non-offset and non-LDA localizer systems). If the angle of offset is thirty degrees or less, the facility is classified as an offset localizer. If the offset angle is greater than thirty degrees, the facility is classified as a localizer-type directional aid (LDA). As a "directional aid," and only a Category I (CAT I) approach, rather than a full-fledged instrument landing system (ILS), the LDA is more commonly used to help the pilot safely reach a point near the runway environs, where he or she hopefully can see the runway, at which point he or she will proceed and land visually, as opposed to (for example) full Category III (CAT III) ILS systems that allow a pilot to fly, without visual references, very close to the runway surface (usually about 100 ft) depending on the exact equipment in the aircraft and on the ground.

An LDA uses exactly the same equipment to create the course as a standard localizer used in ILS. An LDA approach also is designed with a normal course width, which is typically 3 to 6 degrees. (At each "edge-of-course," commonly 1.5 or 3 degrees left and right of course, the transmitted signal is created in such a way as to ensure full-scale CDI needle deflection at and beyond these edges, so the pilot will never falsely believe that he is intercepting the course outside of the actual course area. The area between these full-scale needle deflections is what defines the course width.) An LDA approach (considered a non-precision approach) may have one or more marker beacons, perhaps a DME, and in rare instances a glide slope, just as other precision approaches have, such as ILS approaches.

If the offset is not greater than 30 degrees, straight-in approach minima may be published; circling minima only are published when offset exceeds 30 degrees.^[1]^[2]

List of LDA approaches in the United States

The following 29 LDA approaches are available in the United States (as of June 2016):^[3]^[4]^[5]

List of LDA approaches outside the United States

List of Decommissioned LDA approaches

See also

References

1. ^AIM, 1-1-9c2
2. ^As of September 2011, there are LDA approaches which have straight-in minima published despite the localizer being offset more than 30 degrees: e.g., "LDA/DME RWY 19" and "ROSSLYN LDA RWY 19" approaches to Runway 19 at DCA have 145 and 147 degrees respectively on their final approach course to the airport.
3. ^This count reflects only clearly distinct approaches, i.e. if multiple LDA approach procedures to the same runway are available (all of which use the same localizer) they are counted as one. For instance, KSFO has "LDA/DME RWY 28R" and "LDA PRM RWY 28R (SIMULTANEOUS CLOSE PARALLEL)" approaches, which are essentially two different versions of the same approach, the latter one developed specifically for use in simultaneous parallel approaches to runways 28R (using LDA) and 28L (using ILS or RNAV). On the other hand, KDCA has two different LDA approaches to runway 19, which use different localizers, so they are both counted individually.
4. ^{{cite web |url=http://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/ |title=Digital – Terminal Procedures Publication (d-TPP)/Airport Diagrams |publisher=FAA |accessdate=2016-06-06}}
5. ^{{cite web |url=http://www.faa.gov/air_traffic/flight_info/aeronav/procedures/ |title=Instrument Flight Procedures Information Gateway |publisher=FAA |accessdate=2016-06-06}}
6. ^Amendment 5 to DCA’s River Visual Runway 19 approach, June 5, 2015, by the FAA