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 100Â 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.
List of LDA approaches in the United States
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The following 29 LDA approaches are available in the United States (as of June 2016):
- PAJN, LDA X RWY 08, Juneau International Airport, Juneau, AK
- PAPG, LDA/DME-D, Petersburg James A. Johnson Airport, Petersburg, AK
- PASI, LDA/DME RWY 11, Sitka Rocky Gutierrez Airport, Sitka, AK
- PAVD, LDA/DME-H, Valdez Pioneer Field, Valdez, AK
- PAWG, LDA/DME-C and LDA/DME-D, Wrangell Airport, Wrangell, AK
- KFYV, LDA/DME RWY 34, Drake Field, Fayetteville, AR
- KBIH, LDA/DME RWY 16, Eastern Sierra Regional Airport, Bishop, CA
- KCCR, LDA RWY 19R, Buchanan Field, Concord, CA
- KSFO, LDA/DME RWY 28R and LDA PRM RWY 28R, San Francisco International Airport, San Francisco, CA
- KSNA, LDA/DME RWY 20R, John Wayne Airportâ€"Orange County, Santa Ana, CA
- KTVL, LDA/DME-1 RWY 18 and LDA/DME-2 RWY 18, Lake Tahoe Airport, South Lake Tahoe, CA
- KVNY, LDA-C, Van Nuys Airport, Van Nuys, CA
- KEGE, LDA/DME RWY 25, Eagle County Regional Airport, Eagle, CO
- KGJT, LDA/DME RWY 29, Grand Junction Regional Airport, Grand Junction, CO
- KHFD, LDA RWY 02, Hartfordâ€"Brainard Airport, Hartford, CT
- KDCA, LDA Y RWY 19, Ronald Reagan Washington National Airport, Washington, DC (No longer in use)
- KDCA, LDA Z RWY 19, Ronald Reagan Washington National Airport, Washington, DC
- PHNL, LDA/DME RWY 26L, Honolulu International Airport, Honolulu, HI
- KMTN, LDA RWY 33, Martin State Airport, Baltimore, MD
- KEKO, LDA/DME RWY 24, Elko Regional Airport, Elko, NV
- KLGA, LDA-A, La Guardia Airport, New York, NY
- KDLS, LDA/DME RWY 25 and COPTER LDA/DME RWY 25, Columbia Gorge Regional Airport, The Dalles, OR
- KAMA, LDA/DME RWY 22, Rick Husband Amarillo International Airport, Amarillo, TX
- KSGU, LDA/DME RWY 19, St. George Regional Airport, Saint George, UT
- KSLC, LDA/DME RWY 35, Salt Lake City International Airport, Salt Lake City, UT
- KROA, LDA Y RWY 06 and LDA Z RWY 06, Roanoke Regional Airport, Roanoke, VA
- KVUO, LDA-A, Pearson Field, Vancouver, WA
- KEKN, LDA-C, Elkinsâ€"Randolph Countyâ€"Jennings Randolph Field, Elkins, WV
- W99, LDA/DME-B, Grant County Airport, Petersburg, WV
List of LDA approaches outside the United States
- This list is incomplete
- BIAR, LDA RWY 01, offset 26°, Akureyri Airport, Akureyri, Iceland
- EKVG, LDA RWYs 12 & 30, offset 14° & 2° respectively, Vágar Airport, Vágar, Faroe Islands
- LLBG, LDA RWY 30, offset 11°, Ben Gurion Airport, Tel Aviv, Israel
- RJTT, LDA RWY 22 and LDA RWY 23, Tokyo International Airport, Tokyo, Japan
- RCSS, LDA RWY 28, offset 8° Taipei Songshan Airport, Taipei, Taiwan
List of Decommissioned LDA approaches
- This list is incomplete
- (X)VHHH, LDA RWY 13, Kai Tak Airport, Kowloon Bay, Hong Kong
See also
- Instrument approach
- Instrument landing system
- Simplified directional facility
- Localizer
References
- Aeronautical Information Manual (AIM), published in the USA by Federal Aviation Administration
