Localizer Type Directional Aid
Encyclopedia
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 beacon
s, 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.
Localizer
In aviation, a localizer is one of the components of an Instrument Landing System , and it provides runway centerline guidance to aircraft. In some cases, a course projected by localizer is at an angle to the runway . It is then called a Localizer Type Directional Aid...
-based instrument approach
Instrument approach
For aircraft operating under instrument flight rules , an instrument approach or instrument approach procedure is a series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing, or to a point...
to an airport
Airport
An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...
. It is used in places where, due to terrain and other factors, the localizer antenna array is not aligned with the runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
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
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
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
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
(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
Localizer
In aviation, a localizer is one of the components of an Instrument Landing System , and it provides runway centerline guidance to aircraft. In some cases, a course projected by localizer is at an angle to the runway . It is then called a Localizer Type Directional Aid...
used in ILS
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
. 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 beacon
Marker beacon
A marker beacon is a particular type of VHF radio beacon used in aviation, usually in conjunction with an instrument landing system , to give pilots a means to determine position along an established route to a destination such as a runway...
s, perhaps a DME
Distance Measuring Equipment
Distance measuring equipment is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals....
, 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
The following 31 LDA approaches are available in the United States (as of June 2011):- PAJN, LDA X RWY 08, Juneau International AirportJuneau International AirportJuneau International Airport is a public-use airport and seaplane base located seven nautical miles northwest of the central business district of Juneau, a city and borough in the U.S. state of Alaska...
, Juneau, AK - PAPG, LDA/DME-D, Petersburg James A. Johnson AirportPetersburg James A. Johnson AirportPetersburg James A. Johnson Airport is a public airport located one mile southeast of the central business district of Petersburg, a city in the Petersburg Census Area of the U.S. state of Alaska. The airport has a single runway. Airline service is subsidized by the Essential Air Service...
, Petersburg, AK - PASI, LDA/DME RWY 11, Sitka Rocky Gutierrez AirportSitka Rocky Gutierrez AirportSitka Rocky Gutierrez Airport is a public airport owned and operated by the State of Alaska located on Japonski Island in southwestern Sitka, Alaska, U.S....
, Sitka, AK - PAVD, LDA/DME-H, Valdez Pioneer Field, Valdez, AK
- PAWG, LDA/DME-C and LDA/DME-D, Wrangell AirportWrangell AirportWrangell Airport is a public airport located one mile northeast of the central business district of Wrangell, Alaska. The airport has a single runway. Airline service is subsidized by the Essential Air Service program.- Airline and destinations :...
, Wrangell, AK - KFYV, LDA/DME RWY 34, Drake FieldDrake FieldDrake Field is a city-owned public-use airport located three nautical miles south of the central business district of Fayetteville, in Washington County, Arkansas, United States...
, Fayetteville, AR - KBIH, LDA/DME RWY 16, Eastern Sierra Regional AirportEastern Sierra Regional AirportEastern Sierra Regional Airport is a public-use airport located two nautical miles east of the central business district of Bishop, in Inyo County, California, United States...
, Bishop, CA - KCCR, LDA RWY 19R, Buchanan Field, Concord, CA
- KSFO, LDA/DME and LDA PRM RWY 28R, San Francisco International AirportSan Francisco International AirportSan Francisco International Airport is a major international airport located south of downtown San Francisco, California, United States, near the cities of Millbrae and San Bruno in unincorporated San Mateo County. It is often referred to as SFO...
, San Francisco, CA - KSNA, LDA RWY 19R, John Wayne Airport-Orange CountyJohn Wayne AirportJohn Wayne Airport is an airport in an unincorporated area in Orange County, California, with its mailing address in the city of Santa Ana, which is also the county seat, hence the International Air Transport Association airport code. The main entrance to the airport is off of MacArthur Blvd in...
, Santa Ana, CA - KTVL, LDA/DME-1 RWY 18 and LDA/DME-2 RWY 18, Lake Tahoe AirportLake Tahoe AirportLake Tahoe Airport is a public airport located three miles southwest of South Lake Tahoe, serving El Dorado County, California, USA. This general aviation airport covers and has one runway. The airport is sometimes called Tahoe Valley Airport.The airport formerly offered commercial to several...
, South Lake Tahoe, CA - KVNY, LDA-C, Van Nuys AirportVan Nuys AirportVan Nuys Airport is a public airport located in Van Nuys in the San Fernando Valley section of the city limits of Los Angeles, California, United States. No major commercial airlines fly into this airport; it is used by private, chartered, and small commercial aircraft...
, 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 AirportHartford-Brainard Airport- See also :* Bradley International Airport * Connecticut World War II Army Airfields- External links :* at Connecticut DOT website...
, Hartford, CT - KDCA, LDA/DME RWY 19, Ronald Reagan Washington National AirportRonald Reagan Washington National AirportRonald Reagan Washington National Airport is a public airport located south of downtown Washington, D.C., in Arlington County, Virginia. It is the commercial airport nearest to Washington, D.C. For many decades, it was called Washington National Airport, but this airport was renamed in 1998 to...
, Washington, DC - KDCA, ROSSLYN LDA RWY 19, Ronald Reagan Washington National AirportRonald Reagan Washington National AirportRonald Reagan Washington National Airport is a public airport located south of downtown Washington, D.C., in Arlington County, Virginia. It is the commercial airport nearest to Washington, D.C. For many decades, it was called Washington National Airport, but this airport was renamed in 1998 to...
, Washington, DC - PHNL, LDA/DME RWY 26L, Honolulu International AirportHonolulu International AirportHonolulu International Airport is the principal aviation gateway of the City & County of Honolulu and the State of Hawaii and is identified as one of the busiest airports in the United States, with traffic now exceeding 21 million passengers a year and rising.It is located in the Honolulu...
, Honolulu, HI - KMTN, LDA RWY 33, Martin State AirportMartin State AirportMartin State Airport is a public use airport located nine nautical miles east of the central business district of Baltimore, in Baltimore County, Maryland, United States...
, Baltimore, MD - KSTL, LDA/DME and LDA PRM RWY 30L, Lambert-St Louis International Airport, Saint Louis, MO
- KEKO, LDA/DME RWY 23, Elko Regional AirportElko Regional AirportElko Regional Airport , formerly known as Elko Municipal Airport, is a city-owned public-use airport located one mile west of the central business district of Elko, a city in Elko County, Nevada, United States. This airport serves much of northeastern Nevada.The airport was named J.C. Harris Field...
, Elko, NV - KLGA, LDA-A, La Guardia Airport, New York, NY
- KCLE, LDA/DME RWY 06R and LDA PRM RWY 06R, Cleveland-Hopkins International Airport, Cleveland, OH
- KCLE, LDA/DME RWY 24L and LDA PRM RWY 24L, Cleveland-Hopkins International Airport, Cleveland, OH
- KDLS, LDA/DME RWY 25 and COPTER LDA/DME RWY 25, Columbia Gorge Regional/The Dalles MuniColumbia Gorge Regional AirportColumbia Gorge Regional Airport , also referred to as The Dalles Municipal Airport, is a public airport located in Klickitat County in the U.S. state of Washington, two miles northeast of the city of The Dalles in the state of Oregon. The airport is jointly owned by the city of The Dalles and...
, The Dalles, OR - KAMA, LDA/DME RWY 22, Rick Husband Amarillo International AirportRick Husband Amarillo International AirportRick Husband Amarillo International Airport is a public airport located six miles east of the central business district of Amarillo, a city in Potter and Randall Counties, Texas, United States...
, Amarillo, TX - KDXZ, LDA/DME RWY 19, St. George Municipal AirportSt. George Municipal AirportSt. George Municipal Airport was a public airport located in the city of St. George, serving southern Utah. The airport had one runway. It was mostly used for general aviation and was also served by St. George-based SkyWest Airlines on behalf of Delta Air Lines and United Airlines. SkyWest had...
, Saint George, UT - KROA, LDA RWY 06, Roanoke Regional/Woodrum FieldRoanoke Regional AirportRoanoke Regional Airport , also known as Woodrum Field, is a public airport located approximately north of downtown Roanoke, Virginia, United States. It has two runways and over 60 scheduled flights each day...
, Roanoke, VA - KVUO, LDA-A, Pearson FieldPearson FieldPearson Field , is a city-owned public-use airport located one mile southeast of the central business district of Vancouver, a city in Clark County, Washington, United States....
, Vancouver, WA - KEKN, LDA-C, Elkins-Randolph County-Jennings Randolph Field, Elkins, WV
- W99, LDA/DME-B, Grant County Airport, Petersburg, WV
See also
- Instrument approachInstrument approachFor aircraft operating under instrument flight rules , an instrument approach or instrument approach procedure is a series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing, or to a point...
- Instrument landing systemInstrument Landing SystemAn instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
- Simplified Directional FacilitySimplified Directional FacilitySimplified Directional Facility or SDF is a localizer-based instrument non-precision approach to an airport, which provides final approach course similar to Instrument Landing System and Localizer Type Directional Aid approaches, although not as precise.The SDF signal is fixed at either 6 or 12...
- LocalizerLocalizerIn aviation, a localizer is one of the components of an Instrument Landing System , and it provides runway centerline guidance to aircraft. In some cases, a course projected by localizer is at an angle to the runway . It is then called a Localizer Type Directional Aid...