Monroav,
As an ex pilot/examiner, you have a good understanding of how things work, so I'm not trying to teach you to "suck eggs" here, but I'll keep it simple so others can follow it :-)
- For ATC to control an aircraft, the aircraft needs a radio - nothing else
- ATC use primary radar to see aircraft. Radar sends out a signal, it's reflected off the aircraft back to the radar receiver and the controller sees a "blip" on the radar. No aircraft label, just a dot.
- ATC now dictate that to fly in controlled airspace, the aircraft must have a Secondary Radar (SSR) transponder. New bit of kit strapped to the ATC radar antenna that sends out a "request information" signal to the transponder in the aircraft. The transponder sends back a 4 digit code between 0000 and 7777.
- The aircraft transponders develop and are connected to the altimeter so that they send the altitude too.
- Computer at ATC centre recognises aircraft code and converts it to a callsign on the radar screen. Altitude is also displayed as a flight level, and other information from the ATC computer can be displayed too.
Simplifying things greatly, that is where we are today. You can control using primary radar and just see a blip on the screen (very frightening!) or with the primary blip and the Secondary label (much, much better) or with Secondary alone. The problem controlling with Secondary radar alone, is that it only show aircraft with a transponder, so small aircraft without a transponder and aircraft with an electrical failure will not show up on the controllers display at all - not good!
SSR boxes are developed and get cleverer. They don't need that "request information" signal from the ground any more, as they regularly transmit the information without being asked. They still send out the 0000 to 7777 code and altitude, but they can also send additional information such as speed, rate of climb and descent etc. These new SSR transponders are Mode S transponders and they fitted as the new "standard" fit to aircraft.
With the capabilities of the new Mode S box, it becomes clear that it could be possible to control an aircraft without any ground "radar" stations, so a new standard - ADS-B - is decided upon. Loads more data capability now, so the Mode S ADS-B box is linked to the GPS in the aircraft and data uplinks are made available so the controller can send instructions to the pilot without actually transmitting on the radio. This is the future!
However, you don't need a Mode S transponder and aircraft operators are not required to fit them. Almost all new public transport aircraft will be almost certainly be fitted with them, but as all you need to be legal is the old box that sends out the 4 digit code and the altitude, why bother upgrading an old aircraft?
So, an executive jet will report its position in the following way:
- By radio - only acceptable when receiving a non-radar procedural service
- By being detected by primary radar - the "blip" on the controllers screen
- Be being detected by secondary (SSR) radar - a 4 digit code and altitude information.
RadarBox only detects the Mode S transmissions from aircraft, so without a Mode S box, it's not going to show in the aircraft list or on the map. If the executive jet has an early Mode S transponder, then it will show up in the RadarBox aircraft list only.
If the executive jet has a newer full ADS-B Mode S transponder, then it will show up in the RadarBox aircraft list and on the map unless it is set not to transmit a position, in which case it will only show up in the list.
So, back to your original question, why don't executive jets show on the map? Because operator chooses not to transmit the position information in order to provide a degree of confidentiality to their clients. This doesn't affect ATC one little bit, as they are using primary and secondary radar to control the aircraft, not the additional ADS-B information available from the latest Mode S boxes.
Hope this helps
Allocator
