Transponder Landing System
Encyclopedia
A transponder landing system (TLS) is an all-weather, precision landing system that uses existing airborne transponder
Transponder (aviation)
A transponder is an electronic device that produces a response when it receives a radio-frequency interrogation...

 and 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) equipment to create a precision approach at a location where an ILS would normally not be available.

Description

Conventional ILS systems broadcast using a number of "single purpose" antennas. One, located just off the end of the runway, provides a fan-shaped signal for azimuth direction (side to side) and another located beside the runway provides elevation to indicate a standard glideslope. ILS installations also include one or more "marker beacons" located off the end of the runway to provide distance indications as the aircraft approaches the runway. This complex set of antennas is expensive to install and maintain, and are often difficult to site in built-up areas.

The TLS facility interrogates the transponder
Transponder (aviation)
A transponder is an electronic device that produces a response when it receives a radio-frequency interrogation...

 of the aircraft. After receiving a response, it determines the aircraft's location using two sets of direction finding antenna arrays: one for horizontal position, the other for vertical. It then calculates the signal that the aircraft would "see" if they were located at that location and approaching a conventional ILS system, and then broadcasts that signal to the aircraft. The aircraft's ILS receivers receive a signal that is indistinguishable from a normal ILS signal, and displays this information on their glideslope and 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...

 displays. TLS can also produce 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...

-like audio to indicate distance at appropriate times during the approach. All the pilot has to do is tune in the TLS system as if it were an ILS.

A TLS can be installed in areas where a conventional ILS would not fit or would not function properly, like, for example, an airport that doesn't have a proper reflecting surface for an ILS glideslope because of uneven terrain like steep hills or mountains, or airports that have large buildings like hangar
Hangar
A hangar is a closed structure to hold aircraft or spacecraft in protective storage. Most hangars are built of metal, but other materials such as wood and concrete are also sometimes used...

s or parking garages that create disruptive reflections that would prevent an ILS localizer from being used. TLS does not even have to be installed at a particular location relative to the runway, but can "offset" its signals from wherever it is installed to appear as if it were at the end of the runway. This makes it much less expensive to install while still providing ILS-class blind-landing approaches. As of 2001, TLS was certified by the FAA for Category I ILS usage.

Radio-navigation aids must keep a certain degree of accuracy (given by international standards, FAA, ICAO...); to assure this is the case, Flight inspection
Flight inspection
The evaluation process, using properly equipped aircraft, regarding continuity, integrity and accuracy of significant parameters from radio navigation aids and procedures, aiming their calibration with international standards....

 organizations check periodically critical parameters with properly equipped aircraft to calibrate and certify TLS precision.

Benefits

One of the primary benefits of TLS is the ability to function using equipment that is currently widely used by the aviation industry. TLS uses the existing transponder equipment to determine the aircraft's position. It then transmits the correct signal on the same frequencies used for the current ILS system. All the aircraft is required to do is set the transponder to the assigned code and tune an ILS receiver to the appropriate frequency. As of 2005, modern GPS systems, such as Wide Area Augmentation System
Wide Area Augmentation System
The Wide Area Augmentation System is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System , with the goal of improving its accuracy, integrity, and availability...

 (WAAS) and Local Area Augmentation System
Local Area Augmentation System
The Local Area Augmentation System is an all-weather aircraft landing system based on real-time differential correction of the GPS signal. Local reference receivers located around the airport send data to a central location at the airport. This data is used to formulate a correction message, which...

 (LAAS), have not gained wide acceptance and there is not a large user base. TLS uses equipment most airplanes already have.

For military users, TLS also provides a Precision Approach Radar
Precision Approach Radar
Precision approach radar is a type of radar guidance system designed to provide lateral and vertical guidance to an aircraft pilot for landing, until the landing threshold is reached. After the aircraft reaches the decision height or decision altitude , guidance is advisory only...

 (PAR) graphic display of aircraft position compared to the desired approach course in order for a PAR operator to provide talk-down guidance to the pilot.

Drawbacks

Since the system locks on to a single aircraft's transponder then transmits a signal that is specific to that aircraft's location, only one aircraft at a time can fly the landing approach
Final approach (aviation)
A final approach is the last leg in an aircraft's approach to landing. In aviation radio terminology, it is often shortened to "final".In a standard airport landing pattern, which is usually used under visual meteorological conditions , aircraft turn from base leg to final within one to two miles...

. Any other aircraft in the area will receive the same guidance regardless of their location relative to the approach.

TLS systems are privately operated and maintained. However, unlike standard ILS equipment, the US Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

 (FAA) is not publishing approach procedures for TLS facilities. This leaves the approaches to be determined by the local airport. TLS approach procedures are designated Special Instrument Approach Procedures and require special aircrew training.

Variations

For mobile applications, primarily of interest to the military, there is a variety of electronics packaging available including transportability by trailer, HMMWV or NATO shelter.

Future

It is likely that TLS will be installed in locations that prohibit conventional ILS systems.

See also

  • 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...

  • Precision approach
  • Precision approach radar
    Precision Approach Radar
    Precision approach radar is a type of radar guidance system designed to provide lateral and vertical guidance to an aircraft pilot for landing, until the landing threshold is reached. After the aircraft reaches the decision height or decision altitude , guidance is advisory only...

  • Secondary surveillance radar
    Secondary surveillance radar
    Secondary surveillance radar is a radar system used in air traffic control , that not only detects and measures the position of aircraft i.e. range and bearing, but also requests additional information from the aircraft itself such as its identity and altitude...

  • Instrument flight rules
    Instrument flight rules
    Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....

     (IFR)
  • VHF Omni-directional Range
    VHF omnidirectional range
    VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...

     (VOR)
  • Distance Measuring Equipment
    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....

     (DME)
  • Non-Directional Beacon
    Non-directional beacon
    A non-directional beacon is a radio transmitter at a known location, used as an aviation or marine navigational aid. As the name implies, the signal transmitted does not include inherent directional information, in contrast to other navigational aids such as low frequency radio range, VHF...

     (NDB)
  • Santa Cruz Air Force Base
    Santa Cruz Air Force Base
    Santa Cruz Air Force Base – BASC is a base of the Brazilian Air Force located in Rio de Janeiro, Brazil.-History:The base was originally called Bartolomeu de Gusmão Airport and it was constructed to handle the operations with the rigid airships Graf Zeppelin and Hindenburg...


External links

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