Localizer type directional aid
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 three degrees or less, the facility is classified as an offset localizer. If the offset angle is greater than three 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, right down to the runway surface or very close to it 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.
List of LDA approaches in the United States
- 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 RWY 19R, John Wayne Airport-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, Hartford-Brainard Airport, Hartford, CT
- KDCA, LDA/DME RWY 19, Ronald Reagan Washington National Airport, Washington, DC
- KDCA, ROSSLYN LDA 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 23, Elko Regional Airport, Elko, NV
- KLGA, LDA-A, La Guardia Airport, New York, NY
- KCLE, LDA/DME RWY 06R, Cleveland-Hopkins International Airport, Cleveland, OH
- KCLE, LDA/DME RWY 24L, Cleveland-Hopkins International Airport, Cleveland, OH
- KDLS, LDA/DME RWY 25 and COPTER LDA/DME RWY 25, Columbia Gorge Regional/The Dalles Muni, The Dalles, OR
- KAMA, LDA/DME RWY 22, Rick Husband Amarillo International Airport, Amarillo, TX
- KSGU, LDA/DME RWY 19, St. George Municipal Airport, Saint George, UT
- KROA, LDA RWY 06, Roanoke Regional/Woodrum Field, Roanoke, VA
- KVUO, LDA-A, Pearson Field, Vancouver, WA
- KEKN, LDA-C, Elkins-Randolph County-Jennings Randolph Field, Elkins, WV
- KSLC, LDA/DME RWY 35, Salt Lake City International Airport, Salt Lake City, UT
- W99, LDA/DME-B, Grant County Airport, Petersburg, WV
- AIM, 1-1-9c2
- 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.
- 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 (SIM CLOSE PAR)" 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). On the other hand, KDCA has two different LDA approaches to runway 19, which use different localizers, so they are both counted individually.
- "digital - Terminal Procedures Publication (d-TPP)/Airport Diagrams". FAA. Retrieved 2013-07-06.