Primary, SSR? ASD-B?

[Gustavo Valdez]

Hey Everyone!

So for the last 2 months or so I've been really into developing our new sector with Vatsys, it's been quite a journey with questions, answers that lead to more question, etc. You know the drill, which takes me to today's question.

So last week I finally tracked down everysingle Radar Station in Mexico so it can be properly simulated on Vatsys (Thanks again to @Jake Sawfor properly simulating radar types and it's returns!). When I was finally done I noticed something interesting... Most of Mexico's airspace only has MSSR coverage, something which is now properly simulated in our sector!

The thing is... Idk what that means! I mean, I know Primary is the Radar Echo return with no other information that pretty much position, and that SSR is the Mode C or Mode S. But, what does this mean for the controller, what's should the controller be aware of when controlling a PRI + SSR target vs a purely SSR target. On a plus, if someone can point me on the same direction but for ADSB, like what does it mean for the controller pure ADSB, ASDB + Secondary etc.

Cheers

[Jake Saw]

Primary is useful in high density airspace (typically TMA's) where a transponder failure or someone penetrating a control zone without a clearance can really ruin your day. You can see everyone.

SSR requires aircraft to have an operating transponder but the position of the aircraft is still determined by the radar. For controllers the main difference between Mode A/C and Mode S is the extra information that Mode S provides. For example, the pilot entered Flight ID (Callsign) is visible and very useful for dealing with uncoupled tracks where otherwise you could only see the squawk code. 

ADSB presents essentially the same information as Mode S to the controller. However unlike SSR - ADSB presents the GPS position as reported by the aircraft which means that any RAIM outages or avionics issues can upset it's use. 

There is an emerging variation of ADSB called Space-Based ADSB. The only difference is instead of the receiver being located on the ground - the receivers are in space on satellites. This will allow greatly reduced (but not full surveillance) separation standards in Oceanic airspace for example. vatSys doesn't implement this yet but will in the future. 

The rules for what can be used for separation will vary country to country, but here in Australia Primary, SSR and ADSB can all be used to provide either 3NM or 5NM surveillance separation. Something a controller will have to consider is the continuation of surveillance as the aircraft approaches the edge of coverage - if they leave SSR, does the aircraft have ADS-B equipped or do I need to set up a procedural standard?  vatSys provides the different track symbols and label items to support this. 

 

[Andreas Fuchs]

Here's a collection of useful pages for some of the topics:

ADS-B: https://skybrary.aero/index.php/Automatic_Dependent_Surveillance_Broadcast_(ADS-B)

ADS-C: https://www.skybrary.aero/index.php/Automatic_Dependent_Surveillance_-_Contract_(ADS-C)

ADS-information at Wikipedia (quite accurate): https://en.wikipedia.org/wiki/Automatic_dependent_surveillance_–_broadcast

[Magnus Meese]

On 10/13/2020 at 12:16 AM, Gustavo Valdez said:

The thing is... Idk what that means! I mean, I know Primary is the Radar Echo return with no other information that pretty much position, and that SSR is the Mode C or Mode S. But, what does this mean for the controller, what's should the controller be aware of when controlling a PRI + SSR target vs a purely SSR target. On a plus, if someone can point me on the same direction but for ADSB, like what does it mean for the controller pure ADSB, ASDB + Secondary etc.

Cheers

Depends on the country/unit and its procedures and laws. Some places require an increase in separation and/or change in procedures if they lose PSR or SSR in a coupled system. Some places have cut out PSR all together and can operate with 3nm/5nm with only SSR as it is a well-tested system, saving the costs surrounding maintaining and powering (PSRs require quite a bit of power) the PSR aerials. The few places I know of who's cut out the PSR for civilian use still has their air force monitor air traffic with their own means, so aircraft can't expect to completely disappear by turning off their transponder if they're up to no good, but the civilian guys will be limited to whatever info the military passes on to them. Some sectors, like Shanwick/Gander oceanic, are now using space-based ADS-B to bring surveillance-based ATC to a piece of airspace previously limited 100% to procedural ATC. With domestic units, ADS-B is to SSR these days what SSR was to PSR a few decades ago. Some use it to its fullest, some use it to a certain degree, some don't.

Essentially, it's down to what is approved for normal ops in each specific case. Each unit has its own set of procedures based on the equipment they have installed, and these procedures are vetted and approved by the relevant aviation authority. One country's CAA may be happy approving SSR-only 3nm/1000ft surveillance procedures, another country's CAA may think it is madness to not corroborate the SSR signal with a PSR return and refuse to approve anything less than 5/10/X NM for SSR-only.

For the specific Mexican procedures, you'd have to find someone working in Mexican Air Traffic to give you the details, unless they're laid out in the AIP or other public documents.

[Gustavo Valdez]

I totally forgot about this post! Thanks all for the information. 

On 11/29/2020 at 12:56 AM, Magnus Meese said:

For the specific Mexican procedures, you'd have to find someone working in Mexican Air Traffic to give you the details, unless they're laid out in the AIP or other public documents.

I'll probably have to bother SENEAM with an information request hahaha. Thanks