Transponder Landing System
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The Transponder Landing System (TLS) is an all-weather, precision landing system that uses existing airborne transponder and ILS equipment to create a precision approach at a location where an ILS would normally not be available.
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[edit] History
Conventional ILS has certain limitations, such as specific siting criteria and expensive installation. TLS was designed to overcome some specific limitations. It was not meant to replace ILS on a national scale, but to allow for a precision approach where one would not normally be available.
[edit] Operation
The TLS facility interrogates the transponder of the aircraft. After receiving a response, it determines the aircraft's location then transmits appropriate signals to the aircraft's ILS instruments. This is displayed as a glideslope-like fly up or fly down and a localizer-like fly left and fly right indication on the aircraft's ILS display. Certain configurations can also produce marker beacon-like audio to indicate distance at appropriate times during the approach.
[edit] Accuracy
As of 2001, TLS was certified by the FAA for Category I ILS usage.
[edit] 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 WAAS and LAAS, have not gained wide acceptance and there is not a large user base. TLS uses equipment most airplanes already have.
A TLS is able to be installed in areas where a conventional ILS would not fit or would not function properly. 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 hangars or parking garages that create disruptive reflections that would prevent an ILS localizer from being used.
Additionally, TLS has less stringent siting criteria, and is less costly to install. A conventional ILS system requires specific reflecting surfaces and complicated antenna phasing. TLS can be installed quickly and with fewer problems for siting the facility.
[edit] 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 approach. 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 FAA is not publishing approach procedures for TLS facilities. This leaves the approaches to be determined by the local airport.
[edit] Variations
There is a similar truck mounted system, called firefly, for military usage.[1]
[edit] Future
It is likely that TLS will be installed in locations that prohibit conventional ILS systems. However, GPS landing systems such as WAAS and LAAS will likely replace these systems once they become widely used.
[edit] See also
- Instrument Landing System
- Precision approach
- Secondary surveillance radar
- Instrument flight rules (IFR)
- VHF Omni-directional Range (VOR)
- Distance Measuring Equipment (DME)
- Non-Directional Beacon (NDB)
[edit] References
- Federal Aviation Administration (December 15, 2004). Order 8200-40B Flight Inspection of the Transponder Landing System (TLS) (pdf). Retrieved on 2005-12-11. Background section explains operation and use of a TLS.
- ANPC, Inc. (2005). TLS commercial products. Retrieved on 2005-12-11.
[edit] External links
- ANPC Product Page
- FAA AIM - 3 paragraph summary of operation
