Radar Screen Labels
 

Folks

Can someone please tell me where the info on your screens comes from! In particular Mode S returns with all the extra stuff. I know about the Mode A/C stuff. Are the Mode S labels (such as aircraft type) sent from the aircraft or are they looked up from a database in ATC using the ICAO address which I know is broadcast?

cheers
smithgd

The callsign transmitted on Mode S is input by the crew on the aircraft. Unfortunately, not all crews do it and often they input inaccurate information.

I can't speak officially but I suspect that the callsigns seen on radar labels are derived from the ATC computer which links the flight plan callsign to the transponder code issued to the aircraft, rather than from Mode S.

Every aircraft has an identifying number - for some reason 16 digits sticks in my mind but I am probably wrong. Think of it like the VIN number on your cars engine chassis. That means that the number identifies the aircraft type for life.

The callsign that ATCOs see on the radar are derived from the allocated squawk - i.e. they are paired up on an individual basis. These squawks have a shelf life so that if an aircraft is delayed for a while, a new squawk may need to be allocated. This means that the squawks can keep being used as there is a finite number.

The other info that ATCOs can see i.e. Mode S (as this is what you are asking) are downlinked from each aircraft i.e. IAS, HDG, Selected Flight Level, ROD/ROC etc. There are hundreds of downloadable items, but ATC only use a handful.

The individual number you are refering to is the ICAO address and is 24bits long, this is linked to the registration of the aircraft and is broadcast from the aircraft.

Callsigns are set by the crew as Heathrow Director points out, however I believe these are broadcast from the aircraft not looked up by an ATC computer, hense the silly ones seen!!

I am not aware of the aircraft type being broadcast, yet the info appears on the screen, so i assume it is obtained from the ATC computer and is found using the ICAO address? Is this so?

smithgd

That depends on the unit. At my unit (not mode S), the code-callsign conversions are entered into a PC manually.

CCDS data
 

At the Prestwick Centre the Code Callsign data (CCS) is derived the Code Callsign Database/Distribution System (CCDS) at Swanwick. The CCS is unique and is tied to the mode 3/A code that the aircraft squawks. This is the same for standard SSR and Mode S secondary radar. Most airports also connect to CCDS so they also have the same information displayed for aircraft as the centres.

CCDS obtains the callsigns from Civil flight plan system NAS and Military equivalent system EDDUS.

Currently the SSR code is the key. Its contained in the system flight plan and in the response from the aircraft transponder. The mode S ID is transmitted from the aircraft but only a few European states are using it.

Only a few privileged units (ie those with enough finance to afford the software) can actually see the full mode S info so if you're working a (for instance) LARS unit based at an airfield, you've wasted you're money transmitting mode S to them.

Primary radar. It tells us where the 'planes are....or were. At my unit we try to remember the info. If we can't remember it we write it on the screen with a yellow chinagraph as an aide memoire. It's important to cross out the old stuff. Or rub it off with an old piece of rag. Or the end of a tie. This helps us stop muddling up the planes. It's also important not to rub off the new stuff by mistake. It also helps if we don't break the pencil or drop it on the floor in the dark to hear it rolling under the console. That's bad news because it means I have to bend down with the torch......if the batteries work. We have a Decca Plot to show us where special lines are. This needs a special light. It helps if the bulb doesn't pop otherwise we have to shine the torch on the screen to see the lines. But if we have to do that we can't see the planes. They serve us carrots in the canteen.

You still wear a tie to work? I thought I was the last controller left to do that (OK I'm only a FISO now but then certain FISOs at other airfields pretend to be controllers..)

Not correct. Callsigns seen on the label display on the radar (which, by inferrence is what your original question asks about) are derived from the ORCAM code that is paired up with a flightplan callsign.

The mode S data (within NATS equipped units) which is always shown, is the SFL.

Mode S data which is available via selection globally (i.e you toggle it on and off and it shows on all targets on your screen) is IAS/HDG/GS.

Mode S data which is available via individual aircraft selection (comes up in a separate box for a specific target) is c/s/HDG/IAS/GSD/ROD/ROC/ etc

I think there's some confusion here. The usual callsign labels are derived from flightplan info linked to the transponder setting given to the aircraft. However, I believe that Mode S "callsigns" are set by the crew. Otherwise why would many of them be in error, or contain nonsense and even "rude" words? Plus, a significant proportion of aircraft do not transmit callsigns. Until about 12 months ago transmitted callsigns were unreliable but they have improved of late, possibly as a result of publicity to crews?

I'm currently looking at Mode S info from 50+ aircraft in the London area, of which around 15 are not transmitting callsigns.

HD you are correct, however the question the original OP asked was vague - The callsign info on an ATCOs screen comes from FP data paired to a specific squawk. is a supposition by the OP that is not correct when talking about what an ATCO sees on his display.

Granted the OP may have been talking purely from an SBS receiver point of view... in which case this is not what an ATCO uses!

I think between all the replies all bases have been covered, and all answers were correct :ok:

...yet! :ok:

My ATSU uses an SBS receiver to find out how far away our planes are.
(It's a bit difficult if our planes don't have Mode S.....)
Maybe we should have saved our money and used this instead.......

Anotherthing is somewhat misleading here - NATS has upgraded some radar sites (CLH, CLX, DEB, Glasgow, Belfast, Allanshill, Lowther Hill, and Sumburgh) which carry a unique code so that only that radar can process the reply from the a/c. These upgraded radars also interrogate on Mode A & C, and the Mode S information is fed into the FDP system via a different route, such that a controller without access to a Mode S enabled radar will still see the information displayed.
This explains why units with Mode S enabled radar displays (MACC, TC and NPC) that have enhanced capability can identify the registration of an a/c squawking 7000, even though the a/c is not displaying a squawk allocated by NAS. This is the feature which enables spotters with SBS to see a/c registrations, as it is part of the encrypted 24 - bit address of the a/c. Very useful for identifying infringers too!

Nothing misleading at all all callsigns are paired with the unique ORCAM squawk...

NATS as yet do not use SBS receivers to control aircraft radar is the primary(sic) display.

I hope they never do. SBS is a great fun toy but I'd hate to think that my life relied on it..

Unlike the US way of doing it (which is quite sensible), the UK Mode S 24 bit aircraft addresses assigned by the CAA in no way bear any resemblance to an encoded aircraft registration. The ADS-B broadcasts from the aircraft picked up by an SBS box contain the 24-bit address and either a position, Aircraft ID (i.e. callsign / reg) or a velocity vector. It is the Aircraft ID that the SBS uses to provide identity, not the 24 bit address. The 24 bit address has no identity function apart from allowing a ground radar system to uniquely interrogate or for a receiving system (radar, SBS, Multilat, whatever) to correlate replies for tracking. :ok:


While a sizeable ANSP like NATS is highly unlikely to use an SBS box for operational use, give it a couple of years and the system pictures will be augmented with ADS-B extended squitter positions (or in some areas, fill in gaps in radar cover). Its a good job that the avionics manufacturers always get it right and the positions reported by aircraft are always super accurate................:ugh:

RS