When a commercial airport is experiencing poor weather conditions or visibility is otherwise reduced, it switches to its Instrument Landing System. A set of precision radio signals, the ILS provides aircraft with lateral and vertical guidance for safely reaching the runway. A standard ILS set-up includes multiple large radio antennas, hundreds of high powered lights mounted on tower arrays, and hundreds of kilometers of cabling connecting it all.
But what happens if you need ILS guidance for a runway that moves tens-of-meters each year, like the ice runways at the National Science Foundation’s McMurdo Station in Antarctica? A traditional ILS at McMurdo is impractical as moving even just a portion of the equipment would take months. Enter Advanced Navigation & Positioning Corporation’s Transponder Landing System.
The transponder landing system
ANPC’s Transponder Landing System (TLS) equips runways that are inhospitable to standard ILSs, like the ones at McMurdo, with a full Category I ILS approach. ANPC has been ensuring flights can operate year-round and in poor weather conditions at McMurdo since 2021.
It’s not just Antarctica where the TLS is useful. “Our system works where an ILS won’t,” says ANPC President & CEO Jeff Mains. That’s any airport where a traditional ILS implementation may be impractical, like airports nestled in mountainous terrain, runways that end at the water’s edge, or airports that lack the space for an ILS array for any reason.
How does the TLS work?
The TLS is a “software defined approach” to precision landing guidance, says Mains, and that allows the system to act just like a traditional ILS as far as aircraft and pilots are concerned. Aircraft equipped with Mode S (or Mode 3/A) transponders, ILS localizer and glide slope receiver, Horizontal Situation Indicator (HSI) or Course Deviation Indicator (CDI), can land using the TLS just like they would any ILS.
The TLS itself uses Multilateration, just like Flightradar24 does for Mode S equipped aircraft, to know an aircraft’s position via ground based transponders. It then sends lateral and vertical guidance to the aircraft creating an ILS approach. Given its utility in areas of hazardous terrain, the TLS is capable of segmented or curved approach paths as well as a traditional linear path.
Setting up the transponder landing system
The ANPC TLS is actually three systems in one, a precision approach radar (suitable for military applications), a secondary surveillance radar, and an ILS. For transportable TLS installations, all of the equipment can be packaged into a standard 20 TEU container and set up in just a few hours.
For one of the TLSs at McMurdo, the speed of installation is less important as the system only needs to be realigned every three years. For the other, being able to quickly deploy the TLS at the start of the busy summer season when Antarctic weather still makes operations unpredictable is a key benefit. It’s this portability that also makes the TLS critical in situations like post-hurricane or earthquake operations as being able to quickly return ILS capability to an airfield can speed the delivery of relief flights.
Tracking flights using the TLS at McMurdo
Flightradar24 receivers at McMurdo Station enable users to track flights arriving using the transponder landing system. International flights nearly always depart New Zealand and fly south, coming into TLS range about 60 nautical miles out from the runway. Most flights occur during the Antarctic summer season (November through February), though thanks to the TLS and other equipment, McMurdo is able to operate year-round.
Images of the TLS in Antarctica courtesy ANPC.
![An example full flight summary response from the Flightradar24 API: { "data": [ { "fr24_id": "0987654321", "flight": "SK1415", "callsign": "SAS1415", "operated_as": "SAS", "painted_as": "SAS", "type": "A20N", "reg": "SE-DOY", "orig_icao": "ESSA", "orig_iata": "ARN", "datetime_takeoff": "2023-01-27T05:15:22", "runway_takeoff": "12R", "dest_icao": "EKCH", "dest_iata": "CPH", "dest_icao_actual": "EPWA", "dest_iata_actual": "WAW", "datetime_landed": "2023-01-27T06:15:10", "runway_landed": "27L", "flight_time": 3600, "actual_distance": 1007.74, "circle_distance": 6245, "category": "Passenger", "hex": "4A91F9", "first_seen": "2023-01-27T05:06:22", "last_seen": "2023-01-27T06:18:10", "flight_ended": "true" } ] }](https://www.flightradar24.com/blog/wp-content/uploads/2025/04/Flight-summary-API-cover-300x148.jpg)
