Transponder landing system

A transponder landing system (TLS) is an all-weather, precision landing system that uses existing airborne transponder and instrument landing system (ILS) equipment to create a precision approach at a location where an ILS would normally not be available.


Conventional ILS systems broadcast using a number of "single purpose" antennas.


دو آنتن موجود در سیستم ILS :

 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.

علاوه بر دو مورد فوق سیستم  ILS نیازمند چند  آنتن مربوط به Beacon  نیز می باشد.


 This complex set of antennas is expensive to install and maintain, and are often difficult to site in built-up areas.

مزیت هایی که در مورد این سیستم نسبت به ILS وجود دارد بیشتر در حوزه هزینه های و امکان نصب در مناطقی است که نصب ILS محدودیت هایی دارد.


One of the primary benefits of TLS is the ability to provide precision ILS guidance where terrain is sloping or uneven,
reflections can create an uneven glide path for ILS causing unwanted needle deflections. 

یکی از معایل ILS :

Additionally, since the ILS signals are pointed in one direction by the positioning of the arrays, ILS only supports straight-in approaches. 



TLS supports approach over rough terrain and provides the ability to offset the approach center-line.


With TLS, the localizer course can have a tailored width at the runway threshold (700 feet and 5 degrees typically) regardless of the runway length.

در سیستم TLS امکان طراحی کردن عرض LOCALIZER Course متناسب با میزان مطلوب در ابتدای باند ، وجود دارد.و این به طول باند بستگی ندارد.



The localizer width characteristics can be selected by the approach designer whereas with an ILS the localizer width is determined by the localizer antenna placement which is usually a consequence of runway length.

بنابر این در TLS دست طراح طرح اپروج باز است تا عرض localizer  را به دلخواه تعیین نماید. در حالی که در ILS این عرض بستگی به محل نصب آنتن لوکلایزر دارد که خود به طول باند بستگی دارد.


For military users, TLS also provides a Precision Approach Radar (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.[4] 


Since the TLS operates using the long range band of SSR (1030/1090 MHz) there is no rain fade such as experienced with a traditional PAR that uses primary radar. 


For a traditional PAR, the ability to track the aircraft position is dependent on the aircraft radar cross section.


TLS is based on transponder multilateration and trilateration and consequently tracks all aircraft that respond to the interrogations.


 Omnidirectional antenna surveillance coverage of the TLS extends to 60 nautical miles.[4]


The TLS functions using airborne equipment that is currently widely used by the aviation industry. 


TLS uses the existing Mode 3/A/C/S transponder equipment to determine the aircraft's position. 


It then transmits the correct signal on the same frequencies used for the current ILS system. 


وظیفه خلبان در صورت درخواست استفاده از TLS  :

All the pilot is required to do is wait for clearance from ATC for the TLS approach and then tune an ILS receiver to the appropriate frequency.


 TLS uses equipment most airplanes already have