ADSB for VFR

[Nobody]

Unless I am mistaken I think that the Levil BOM is only ABS-B in and I suspect only on UAT, their website isnt clear. They do have their beacon product which is ABS-B out but that is UAT.

 

If what I am saying sounds like gibberish...

 

ABS-B out is like your mouth. You use your mouth to talk to someone. ABS-B out broadcasts GPS position data of your aircraft over radio waves to people on the ground and other aircraft.

 

ABS-B In is like your ears. You use your ears to listen to others. ABS-B in is a receiver that takes the position data broadcast by others and lets you view it on a screen.

 

Think of UAT and 1090ES like languages eg Chinese and English. 1090ES is used everywhere in the world. UAT is only used by General Aviation in the USA. 1090ES has some problems if there are a lot of aircraft in close proximity and that is one of the reasons why the US has UAT. UAT lets you send a lot more data over the airwaves and in the USA the FAA broadcast useful information like weather and NOTAMS over UAT to aircraft. The main point to remember when shopping for equipment for use in Australia is that UAT wont work and that it needs to be 1090ES.

 

If you use Avplan or Ozrunways you can get ABS-b In with a Raspbery PI and a SDR dongle. The cost (in aeroplane terms) is minimal. Instructions below:

 

AvPlan Omni

 

ADS-Pi: Low-Cost ADS-B IN for OzRunways

 

 

[Blueadventures]

No. The TT21 is only a transponder with a built in encoder. To be used for ADS-B it needs an external GPS. Trig have one called the TN70 but it is approximately AUD $3000.  

 

Dynon have their SV-GPS-2020 which is about a third the price but has been "accepted" by the FAA in the USA rather than TSO'd. I am not sure if this is accepted in Australia.

 

from: SV-GPS-2020

Also have a 'TN72' gps unit.

 

 

[Kyle Communications]

The latest video I saw from Levil states the BOM does both for ADSB in the Beacon though I asked Ananda whether they will do a 1090 version instead of the UAT and she said they had plans of releasing a 1090 version for the rest of the world

 

 

[Kyle Communications]

I thought I saw it somewhere

 

Page 6 of the manual for the BOM says 978 and 1090 ES

 

http://nebula.wsimg.com/e97289f1beccc39b8fb43e301fd8ecef?AccessKeyId=25B2510C35AB96A7E02E&disposition=0&alloworigin=1

 

 

[Nobody]

There you go!!! It will give people ads-b in on the 1090 frequency which will work in Australia.

 

Edit. I wish manufacturers would make it clear what their products do. In/Out and UAT and 1090ES shouldn't be hidden in the detail in the manual....

 

 

[Garfly]

Okay, sorry, just one more naive question about all this .... ;-)

 

Is this statement correct?: Any Mode S transponder, with altitude encoder - but with no GNSS connected - still gets interrogated and responds in the same way as any current Mode C transponder does. That is, it makes itself conspicuous to existing ATC and TCAS systems in the usual way, via radar (and/or direct air-to-air interrogation).

 

If this is so, I'd have thought that, whilst not fully participating in the ADSB system, a VFR aircraft so equipped (bare-bones Mode S) is at least as compliant as any other with traditional SSR Mode C gear and therefore would be accepted by the system (i.e clearances, separation, eligibility to use Class E etc.) in the same way, for the foreseeable future.

 

But from what I gather above (and from what I glean from the Discussion paper) that ain't really so. It seems that Position-less Mode S will be less acceptable than old Mode C (e.g: not allowed in Class C space). There's something I'm not getting here.

 

If I can just clear up this last bit of confusion I can hurry up and wait for all the techno-regulatory fog to clear.

 

(Put another way ... Why would we need to spend big on an approved GNSS box for our basic Mode S if our main aim was not [yet] to participate fully in ADSB but just to have the pro-safety conspicuity already available with Mode C .... and to be able to qualify for CTA transit, when, and if, that becomes possible for us RAAus mob?)

 

 

[Birdseye]

You are basically correct, but only when within range of a secondary surveillance radar head. Once out of that coverage there will be no positional information without ADS-B fitted.

 

 

[Kyle Communications]

Well asking the question produces the answer....our aircraft operations are run by such a convoluted papwork system and it just seems to be bits added and nothing ever seems to follow the norm most of the rest of the world has. CASA seems to just add bits and pieces...typical of the way our govts operate...NEVER implement a well thought out system because the govt needs to stuff it up here in Australia....sorry if I seem a but cynical

 

 

[Nobody]

In advance, sorry for the long post and what to some will sound very simple....

 

It might be useful to explain some terms and how the different systems work first

 

Primary Radar. You probably know this one but I will start by explaining how it works. A beam of radio waves is sent out from a ground station(or aircraft) and is reflected off a "target". It was developed in the second world war to detect enemy aircraft approaching. A radar beam sweeps around and the reflected radio waves are received. There is no active response from the target just the reflected radio waves. You can think of this as someone with a searchlight sweeping around the horizon, when they shine their light on an aircraft if the reflected light is bright enough you can see it.

 

Secondary Radar. Primary radar was very useful but how do you know that the aircraft you have detected are friendly or enemy. Enter the transponder. By rebroadcasting a radio wave pulse from the aircraft when the beam of the primary radar passes over it. Going back to the searchlight example above you can think of the transponder as a strobe light that is triggered by the search light. Now you dont need to detect the weak reflected radio waves but get a bright pulse generated by the aircraft, the range of detection is increased but you can go one better. By encoding a short message in the return pulse you can sort and identify the targets. The short message is a 4 digit code but the digits run from (0 to 7) and so the system allows for approximately 4000 differing codes. The codes are entered by the pilot into the transponder and then broadcast as part of the radio message. This way you could say to the friendly pilots use code 4057 today. The enemy wouldn't know the code and so you could separate friend from foe. This system developed in to the system we have today called Mode A.

 

Now these types of radar could give you distance to the target at the bearing but getting the altitude is harder. At 60mn away the difference between 5000 feet and 8000 feet is less than half a degree. Some wise cookie realized that if you had an electronic altimeter (called an encoder) in the aircraft you could have the transponder broadcast the aircraft altitude back to the ground station. The base station could work out the bearings and distance from the radar returns and the altitude from the encoder and give a fairy accurate 3D position for aircraft to keep them separated. This is termed Mode C It is important to note that a mode C transponder still broadcasts the code like a mode A transponder. The altitude is in addition to the code so sometimes you see these refereed to as Mode A/C. Also because the accuracy of the encoder is important for maintaining separation this is subject to regular checks and calibration.

 

Now 4000 codes isnt a lot and when you reserve some for emergencies, VFR aircraft and decide that some sequences are likely to be confused you can end up running out of codes in a large airspace system. Also the system relies on pilots putting in the correct code and there have been instances where that hasn't happened correctly. Someone then worked out that you could expand the system to have approximately 16 million different codes by using a 24 digit binary number. Given that there are about 250,000 GA aircraft in the USA and so somewhere around 500,000 total aircraft world wide you can give each one a unique number that can be programmed into the transponder when it is installed. This is called Mode S A mode S transponder will still broadcast the mode A mode and the altitude and so it can be though of a node A,C and S.

 

And finally someone else worked out that you can also add the GPS position onto the return broadcast. This is termed Mode S ES, the ES standing for "extended squitter"

 

Now the next thing is that the transponder is responding to a sweep from a ground based radar system. What if the transponder just broadcast the output every say 2 seconds? You wouldn't need the radar to trigger the transponder. Then Airservices could have a system that gives separation and traffic control without the need for the expensive to maintain ground based radar systems. This is in essence ADS-B.

 

So what does all this mean at the moment for Airspace users? To operate in Class E (and C) airspace you need a Mode C transponder as a minimum, if you have a mode S transponder you are good to go too. Mode A(or no transponder) wont cut it. To operate IFR you need ADS-B out in all classes of airspace, with some exceptions for private aircraft. Airservices would probably like to require ABS-B for VFR in these types of airspace too as it would save them some money. The USA is going down this path, requiring ABS-B out for all users in class C airspace from 2020(but they are also making the fitment of ADS-B to small aircraft as economical as possible)

 

It is worth clarifying a few other points. If you never fly in controlled airspace does a transponder provide any benefit? TCAS is a system that is like airborne radar. It interrogates the transponders of aircraft that are around it and can predict collisions and what action might need to be taken to avoid. All RPT aircraft bigger than a certain size(19 Seats I think but not sure) are required to have it and so it is useful to have a transponder if you are in an areas where RPT operate regularly. They will see you on their screen and know your position and altitude. ADS-B out will improve on this situation by increasing the accuracy of the position and also allowing aircraft with ABS-B in to see you. TCAS is very expensive. ABS-b in can be had by anyone using ozrunways/Avplan for about $100.

 

 

[Garfly]

Wow! Thanks heaps, Nobody. A fantastic run down of the complications and implications - technical and otherwise.

 

It's reassuring to hear "if you have a mode S transponder you are good to go too." (even sans proper ADSB)

 

That I feared otherwise is probably due to my misunderstanding of parts of the Discussion Paper and what Airservices told Derek.

 

Time for another read. ;-)