A transponder (short-for transmitter-responder[1] and sometimes abbreviated to XPDR,[2] XPNDR,[3] TPDR[4] or TP[5]) is a device used in most modern aircraft to make the aircraft more visible to ATC (Air Traffic Control) radar. When an aircraft is illuminated by a radar signal, the transponder sends a code that is displayed on the ATC radar screen. The code, sometimes called a “squawk code” (SQ), is a 4-digit numeric value that is set by the pilot.

Brief History of transponder in SL

Blake Sea presicion Chart v7- diciembre 2010

I'll tell you what I've seen since I've been in SL (2009), so I do not know if others had done before any attempt to build something similar, so I hope to correct me and provide more information to also complete this article.

Lobofeo Kobaleinen, was the creator of maps of air routes in a fairly large area and the most used at that time (before 2009), which included from northern Satori (west to east), most of Nautilus and part of USS / Blake Sea area (see picture at right).

Snap 2015-04-18 at 14.12.19
He was also the creator of the group 119.200 MHz Blake Sea Control Area, the group used for pilot - ATC bot communications in the great supercontinent of SBNCG (Satori, Blake, Nautilus, Corsica, Gaeta V), and I think the most used in SL aviation in the last years for this purpose; in actuality, Lobofeo, as he told me, will continue flying airplanes in real life, because it is a commercial pilot.

On late 2009 and early 2010, Lobofeo began creating boxes with maps and information about aviation, calling them "Map Pack Edition", and in February 2011 started the first series of boxes where it included the first transponder manufactured by Erick Gregan, in the "Map Box Crystal V 8"; currently is still running and in use, and can be obtained one of these boxes at the airport terminal of New Horizons International (see picture at right).

NOTE: in May 2015, the airport of New Horizons is rebuilding and this box is deleted.

In 2013, Maddog Bailey launched its Bailey Flight Transponder a new type of transponder in which, unlike the above, it could put the number of squawk you want, as well as select channels for receive information about airports (then only Miam Airport) with great innovation you can select the channel ATIS airport, one for communication with the tower, one with ground control, one for ATC and another channel as a service UNICOM for use between pilots; the project was very interesting, but needed a big financing as well as repeaters in nearby sims to each airport to control the approach of each aircraft.

Finally, in 2015, Kelly Shergood manufacture a new model of transponder tracking system integrating for see aircraft in the world of SL for the connection outside world in a web page named ATC Radar, using the maps of Google Maps and an interface showing airports (with information of them to the touch), waypoints and track aircraft (shown at the top of each aircraft speed, altitude and flight number or squawk); for me it is a total innovation in what concerns the way of looking at aviation in SL, because without entering SL we see in progress flights and flight plans, similar to those seen here and ear the ATC tower here.

GPS And Transponder emitter  EG Aircraft

Transponder Eg Aircraft V2.0 - Erick Gregan
The transponder of Erick Gregan is simple to use, just annexing it as a HUD, and touching a button to toggle; once activated it connects to the receiving server, and it returns a random number (but not repeated with the other transponders) used to locate the aircraft on the map (on the panel is in the control tower at the airport in New Horizons still can see the data reception system); in said panel a red ball appears above the number of the transponder, and a bottom panel you can see the flight, altitude, speed and sim name which are at any given time.
New Horizons tower and transponding server dashboard
To confirm if it worked yet, I put the HUD and flew around the airport and in the adjoining sim, being able to observe that there not appeared some ball with the number of the transponder and the movement  not is reflected in the panel (incidentally, the panel is filled with red balls, possibly being out of use, and no auto refresh to remove); the system predates the appearance of robots ATC and needed an operator to handle, there is still the chair in which he sat.

NOTE: in May 2015, the airport of New Horizons is rebuilding and the tower receiver is deleted.

Bailey Flight Transponder

Transponder (Beta) - Grid ATC System - Maddog Bailey
ATC Grid System, also called this ambitious project that had the idea to set up in all major airports, with approaches radar located in the control tower and an operator who watched the flights in descends and gave indicacione through the chat group; I still remember when I could see the radar and was has four by four meters, huge and certainly not working at the moment.

The system had a frequency control for channels and can be up to two decimal places in the channel (eg 125.25), and could also be used in a similar way to GridTalkie pilot-pilot communications; was also very good idea ATIS service for a particular channel, not via group chat (as, for example, with 117,900 MHz Group chat, where the East River Intercontinental Airport ATIS transmits its signal every hour); in the case of Maddog transponder, we selected channel ATIS Miami, and was receiving the information in chat every minute, taking just to change the channel to not receive again.

Shergood Aviation – Transponder and ELT HUD

Snap 2015-04-18 at 21.20.04

The Kelly transponder is a great innovation in the idea of ​​following aircraft as the external interface used can perfectly locate the aircraft, its turns, altitude (if not forgotten to put it, that most forget ), also the possibility to put the flight number (I like to also put the ICAO code of the aircraft, for example, MGK1234-E50P, is equal to company MAGEK Airlines, flight number 1234, aircraft type Embraer Phenom 100).

Snap 2015-04-18 at 21.18.20
CRJ-700 IFR demonstration

CRJ-700 IFR demonstration

Its use is quite simple, but has several menus that may frighten those who do not want to complicate your life by touching buttons, but they are necessary if we want to interact with other aviators and make us see on radar; for example:

  • it is important that others see our altitude, so you always get the ALT button
  • the flight plan, to register, only look at the website but when registering we mean that we are responsible and use the standard protocol flight, whether it is in VFR (easier) or IFR
  • the button NOTAM warnings are in the menu, and it's a good habit to always look the map on the website and check for any notice so NOTAM to change the route in our path; if we give notice to see there is a sim where the cross is very slow, very big lag or is there a race with many participants, we help others do not crash puting a NOTAM advise create for us
  • is a good idea to put in STBY the transponder when we completed a flight, so that our aircraft disappears from the screen, not the entered data is lost (to be visible again, only press ALT)
    Two transponders HUD wear effect

The basic transponder is FREE and the webpage is open to all but if you sign up there, you can put your pilot profile, aircraft type and tail number (contact with Kelly for that). And see the use of the transponder integrated in an aircraft in the following video.

NOTE: when you decided use a transponder HUD, wear only ONE (for free or advanced), or you see in the map something similar this.

And now that? Ideas of a possible future for transponders

With the appearance of Kelly Shergood transponder many doors open for things not previously thought, so that the ideas outlined here might look made in the short term (if all interested parties reach an agreement, of course):

  • connect with bots ATC transponder, creating a program to identify aircraft on takeoff, approach and landing at an airport and ATC own giving them directions to the pilot (the current system is only an echo of what the pilot said in chat )
  • using the base of the ATC bot (or creating another system), develop a radio station of information for each airport on a channel (ATIS type, but with more information of the number of avatars in the sim, amount of lag, etc), and can follow the idea of ​​the Maddog Bailey transponder to include a channel for ground control (authorization to start up and takeoffs, terminals available), one for approaches and landings, etc.
  • creation of real-time information panels at each airport using the information from the flight plan
  • Finally, something I think would not be very difficult to do, but that would result like the icing on a chocolate cake: create a website where reproduce audibly sounds (using a text-to-speech) to ATC-pilot transmissions in a group channel, to see on the radar so the existing traffic and conversations in real time; I'm sure more than one then encourage follow protocols flight.


  1. Mangine, Robert (2007). The Truth About Transponders. Retrieved on 2008-12-24.
  2. Farlex, Inc (2008). XPDR. Retrieved on 2008-12-24.
  3. Farlex, Inc (2008). XPNDR. Retrieved on 2008-12-24.
  4. Farlex, Inc (2008). TPDR. Retrieved on 2008-12-24.
  5. Farlex, Inc (2008). TP. Retrieved on 2008-12-24.