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ADS-B and FLightradar24.com Every now and then, something comes along that stops us in our tracks. Google Earth did when it first came out. Shipping AIS did it, too. Now there’s another one: it’s called ADS-B and via certain websites it lets you see, in real time, the location of every commercial aircraft flying anywhere in the world. That’s right – anywhere in the world! W e’re going to ask you to do something a little unusual before you start reading this article. We want you to go to your computer, go online and type in the URL www.flightradar24.com . . . and have a look (give it a few seconds to load). Depending on the time of day, you’re going to see, literally, thousands of aircraft in the air at once! But even more interesting, if you click on a particular ’plane, you’ll see it identified by carrier, type, callsign, origin and destination, eta, track, height, speed and much, much more. Zoom in enough and you’ll see the aircraft move towards its destination, 12  Silicon Chip in most cases right up to the point where it lands and taxis to its slot at the terminal. Choose between a “map view” and a “satellite view” (the latter is much more interesting because it shows airport runways and taxiways). You can also call up loads more data related to the screen you’re viewing – the airports or origin and destination, for example. Or take a closer look at the type of ’plane. Switch to “Cockpit View” and you’ll By Jim Rowe and Ross Tester get a pilot’s-eye view as the plane flies along. Etcetera, etcetera, etcetera! If that hasn’t left you fascinated then we’re sorry – your fascination quotient has obviously been used up. For the rest of us, you’d have to agree that’s pretty amazing. Being able to track aircraft from their point of departure to their point of landing in real time, with basically as much information about that flight as the air traffic controllers have, demonstrates the spectacular advances which have been made – and are still being made – in all facets of electronics. What you’re seeing is the end result of an aircraft information and identisiliconchip.com.au 1090MHz TRANSMITTING ANTENNA GPS ANTENNA HIGH INTEGRITY GPS RECEIVER ADS-B DATA LINK (MODIFIED MODE-S TRANSPONDER) OTHER AVIONICS (PLANE ID, ALTITUDE, SPEED, HEADING, CLIMB) Fig.1: the idea behind ADS-B is quite simple: data from the aircraft is combined with accurate positional information and is transmitted to either satellite or ground receiving stations a couple of times each second. It’s what happens to that data afterwards which makes ADS-B so valuable. fication system called ADS-B, which stands for ‘Automatic Dependent Surveillance – Broadcast’ and these words actually give you quite a few clues regarding what the system does: ‘Automatic’ means that the equipment in an aircraft requires no input from the pilot or external interrogation from either a ground-based secondary radar or another aircraft; it simply ‘does its thing’ automatically; ‘Dependent’ means that the system depends on being fed accurate position, altitude, speed, climb, heading and other navigation data from the aircraft’s avionics system, along with the aircraft’s ID information – again, all automatically; ‘Surveillance’ means that the system provides all of this information to any facility which requires this information, such as ATC (air traffic control) ground stations or other aircraft; and finally ‘Broadcast’ simply means that the information is continually broadcast from the aircraft, in the form of digital data bursts sent twice per second at a frequency of 1090MHz. But what does all this mean? In a nutshell, it means you get to see on your computer screen, in real time and from anywhere in the world there’s a broadband connection, the same information an air traffic controller sees. And then some! If all this is sounding vaguely familiar to you, we featured a somewhat similar idea back in our November 2008 issue. The big difference is for that system, you needed to buy a special AirNav Radar Box for just on a thousand dollars. Now, you don’t have to spend a cent. And in the ensuing five years, the amount of information accessible to you has increased dramatically. “Off-air” version You’ll recall that we’ve been playing around with USB “TV” dongles over the past few months, putting them to uses their developers (probably!) never envisaged. Well, we’ve found yet another use for them – as a receiver for ADS-B signals. We mentioned before that they are all on 1090MHz – well within the capabilities of many of these dongles. So elsewhere in this issue we show you how to “do it yourself” – with appropriate software you connect a suitable aerial which will cover 1GHz (eg, a discone) and away you go. But let’s look a bit closer at ADS-B itself. The Sydney-Melbourne air corridor is regarded as pretty busy – until you compare it with the USA (opposite)! You’ll learn a lot from the flightradar24 website – even if you have never had any interest in aviation. And you’ll waste hours on it . . . Since preparing this article, we note that flightradar24.com has updated its presentation – with even more information! siliconchip.com.au August 2013  13 EACH AIRCRAFT EQUIPPED FOR ADS-B HAS A GPS RECEIVER + A MODE-S TRANSPONDER WHICH AUTOMATICALLY BROADCASTS ADS-B EXTENDED SQUITTER MESSAGES TWICE PER SECOND ON 1090MHz ADS-B RECEIVING STATION RECEIVES & DECODES MESSAGES, SENDS OFF TO ATC Fig.2: each aircraft fitted with ADS-B OUT equipment transmits ADS-B data ‘squitters’ twice a second, to be picked up by ground receiving stations. Where it came from The basic idea is pretty straightforward, as you can see from the explanatory diagrams of Figs.1&2, which show the basic elements of the ADS-B systems. ADS-B had its origins in the aviation transponders developed during World War II by the military in Britain and the USA, initially as a key element in the IFF (Identification Friend or Foe) system used to differentiate between friendly and enemy aircraft. An IFF transponder in each aircraft would respond with the appropriate ‘squawk’ code when interrogated by another aircraft or ground station. (Today’s trivia: the term ‘squawk’ seems to have arisen because IFF was originally code-named ‘Parrot’). Further development occurred in the 1950s, when transponders were adapted to provide squawks with navigation information (like the air- craft’s pressure altitude as well as its designated ID code) when aircraft were interrogated by so-called ‘secondary surveillance radar’ (SSR) or ‘beacon radar’ on the ground. These so-called “Mode A” and “Mode C” transponders were used to provide traffic control services for general civil and commercial aviation. Primary radar at airfields was still used to determine an aircraft’s range and bearing. The next main development came in the late 1980s, when various tragic mid-air collisions between aircraft prompted the US Congress to pass a law mandating that all carrier aircraft operating in US airspace with more than 30 passenger seats would have to be equipped with equipment for TCAS II (Traffic Collision Avoidance System type 2) by 1993. Aircraft with between 10 and 30 seats were required to be fitted with equipment for a simpler TCAS I system. This requirement resulted in the development of “Mode S” transponders, which were designed to provide the additional information for TCAS I and TCAS II when interrogated by either an SSR on the ground or another aircraft. Mode S transponders provided information on the bearing of an aircraft, its altitude and its range from the interrogating transponder. Mode S DF11 Acquisition Squit (1090MHz) – sent 128ms after interrogation 8ms 56ms PREAMBLE CODE PARITY CHECK (PI FIELD) 24 bits DOWNLINK FORMAT (DF) 5 bits AIRCRAFT (ICAO) ADDRESS (AA) 24 bits TRANSPONDER CAPABILITY (CA) 3 bits ADS-B Extended Squitter message format (1090MHz) – broadcast twice per second 8ms PREAMBLE CODE DOWNLINK FORMAT (DF) 5 bits TRANSPONDER CAPABILITY (CA) 3 bits 112ms PARITY CHECK (PI FIELD) 24 bits ADS-B DATA (ME) FIELD 56 bits AIRCRAFT (ICAO) ADDRESS (AA) 24 bits Fig.3: The data format sent by Mode S transponders in response to an interrogation by an SSR(above), compared with the extended squitter broadcast continuously by aircraft with ADSB OUT equipment fitted. Both are on 1090MHz but the ADS-B squitters carry more information. 14  Silicon Chip siliconchip.com.au Sydney International airport, mid-afternoon. There’s one plane just landed on runway 34R, one on final approach to 34L and one to 34R along with another holding short on 34R, ready for its left turn to take off to the north. In order to provide this additional information, Mode S transponders were designed to transmit 64-bit ‘squits’ instead of the squawks transmitted by Mode A and Mode C transponders. TCAS I allows a pilot to see the relative position and speed of all aircraft within a 10-20 mile (16-32km) range. In addition, it provides a collision warning when another aircraft comes too close. TCAS II expands on these provisions by adding information on whether nearby aircraft are climbing, descending or flying level. It also provides information on evasive manoeuvres necessary to avoid a collision. If both aircraft in danger of colliding are fitted with TCAS II equipment, their evasive manoeuvres are coordinated via an air-to-air link. Enter ADS-B ADS-B is essentially an improved version of TCAS technology which provides additional safety and reliability for both pilots and air traffic controllers. It uses high-integrity GPS receivers in each aircraft to continuously monitor its exact position (latitude and longitude), plus a modified Mode S transponder which broadcasts this information automatically twice a second together with the aircraft’s unique ICAO 24-bit Aircraft Address, the Flight Identification, the aircraft’s barometric and geometric altitudes, the rate of climb or descent, the tracking angle (heading) and ground speed. To provide this additional ADS-B siliconchip.com.au One of the planes on final approach in the grab at left is an RAAF Canadair. Here’s the “Cockpit View” option as it lands. With realistic instruments displayed, the software integrates with Google earth. data, Mode S transponders were modified to broadcast 120-bit ‘Extended Squitter’ bursts at 1090MHz. Fig.3 shows at the top the format of the Mode S 64-bit squits used for TCAS, with the format of the 120-bit extended squitter bursts broadcast by ADS-B Mode S transponders shown below for comparison. Because this enhanced information is broadcast continuously at 1090MHz (rather than only in response to SSR interrogation), it can easily be picked up by ADS-B receiving stations on the ground, decoded and then relayed to ATC centres via either a satellite link or the internet. As a result ATC centres can monitor the position and movement of all aircraft fitted with ADS-B which are within range of the ground stations. By the way, officially ADS-B is regarded as comprising two complementary aspects, known as ADSB OUT and ADS-B IN. ADS-B OUT is the aspect where each aircraft broadcasts its own ADS-B information, for surveillance mainly by ground stations. ADS-B IN is the complementary aspect where an aircraft can also receive the ADSB broadcasts from other aircraft in its vicinity, so its pilot can be fully aware of their local environment. At present Australia seems to be requiring aircraft to be fitted only with ADS-B OUT, although many of the aircraft operated by international airlines are likely to be fitted with both. One of the big advantages of ADS-B is that it allows monitoring of aircraft well outside the coverage of both pri- mary and secondary radar. As a result the transition to ADS-B is seeing the gradual phasing out of ATC ground radar installations. Another thing to note is that in the USA, the FAA (Federal Aviation Administration) has authorised two versions of ADS-B. In one version, called ‘1090ES ADS-B’ the ADS-B extended squitters broadcast by each aircraft transponder are at 1090MHz, the frequency used in most other countries including Australia. In the second version, called UAT ADS-B, the ADS-B messages are broadcast at 978MHz using a Universal Access Transceiver (UAT). The FAA intends that 1090ES ADSB will be used by larger and faster aircraft operating at altitudes above 18,000ft, while UAT ADS-B will be used by all general aviation aircraft operating at lower altitudes. The idea of this separation is to alleviate 1090MHz congestion of the ADS-B system in areas where there is a great deal of air traffic. One comment we heard was that, looking at the USA on flightradar24.com, you wouldn’t need to buy a ticket – you could walk across the USA wing to wing! A further refinement in the USA is that, presumably for security and anti-terrorism reasons, the FAA has decreed that the information fed to the internet is delayed by five minutes. And if you look at certain “trouble spot” areas of the world you’ll probably find that ADS-B signals are either turned off as the aircraft approaches the airport or deliberately “mangled”. August 2013  15 For example, at Ben Gurion airport in Tel Aviv planes simply “disappear” below about 8,000ft and at Dubai Airport, landing planes suddenly “take off” again in weird directions (ie, not using the runways!) at strange speeds. Even here in Australia, we were tracking several aircraft landing at Cairns International when they too suddenly disappeared off screen – but the same aircraft landing at Sydney could be followed all the way down, along the taxiways and finally into its bay. We’re sure there are other examples. ADS-B in Australia In our AirNav RadarBox story in 2008, ADS-B was already very well established locally. And in 2009, Australia became the first country in the world to be fully equipped for ADS-B coverage. At that stage there were 57 ADS-B ground stations, operating from 28 sites. These apparently offer complete coverage of the continent for aircraft flying above 20,000ft, with only small gaps between ground station coverage for aircraft flying across remote rural areas at lower altitudes. The coverage around each ground station is within 20 nautical miles on the ground, increasing to over 250 nautical miles at high altitudes. According to Airservices Australia, all aircraft operating at FL290 (29,000ft) will need to be equipped with ADS-B OUT equipment by 12 December 2013. Then on 6 February 2014, all aircraft operating under IFR (Instrument Flight Rules) first regis- tered in Australia after that date will need to be equipped with ADS-B OUT equipment. By February 2017, all aircraft operating under IFR in Australia at all flight levels will need to equipped with ADS-B OUT equipment. (The above rules also apply to helicopters, if they are flown under IFR.) There are currently no requirements for recreational aircraft and other aircraft flown under VFR (visual flight rules) to be equipped for ADS-B, but from February 2014 any aircraft (IFR or VFR) imported to, or manufactured in Australia will be required to be fitted with a Mode S, ADS-B capable transponder - unless it will only be operating in ‘Class G’ airspace below 10,000ft. Note that although ADS-B IN capability will not be mandatory in Australia under the current rules, there will still be a lot of incentive to fit it to aircraft voluntarily in addition to ADS-B OUT. That’s because of the additional pilot information and hence improved safety. North America and other countries In the USA, ADS-B ground segment implementation and deployment for the complete National Airspace System (NAS) began in 2009 and was expected to be completed this year (2013). The complete system was expected to consist of 794 ground stations. The South Florida installation (involving 11 ground stations) was the first to be officially commissioned, Here’s an alternative “map view” showing ’planes over coastal NSW. If the image has printed clear enough, you might see that DAL16 is flying from JFK, New York, to LAX, Los Angeles. But it’s just taken off from SYD, Sydney! 16  Silicon Chip although developmental systems have been online in Alaska, Arizona and along the East Coast since 2004. In Canada, ADS-B was implemented in 2009 to cover its northern airspace around Hudson Bay. The service is being extended to cover areas around the east coast of Canada and Greenland and is expected to be extended to cover the rest of the Canadian Arctic and the remainder of Canada in due course. China had a fully functional UAT ADS-B system operating by March 2009, with eight ground stations spanning over 1200 nautical miles across Central China and over 350 aircraft fitted with UAT ADS-B equipment. Presumably this system has expanded considerably since then. In 2010, 18 ADS-B ground stations began to be installed in Iceland, Greenland and the Faroe Islands, to extend ADS-B coverage across the North Atlantic Ocean. The European Community is adopting ADS-B as part of its planned ATM Network, a unified Air Traffic Management system which will span across the EC countries. The EC is also combining ADS-B with what it calls Independent Surveillance, provided by either MSSR (Monopulse Secondary Surveillance Radar), Mode S (presumably TCAS) or WAM (Wide Area Multilateration). Many of the WAM system receivers incorporate ADS-B functionality. WAM is already implemented in Armenia, Austria, Czech Republic, Spain and the UK (including the North Click on a plane image in the left panel and it will take you to the www.planespotters.net website, with a large photo (and the photographer’s details) and aircraft details underneath. Photo courtesy Planespotters, © Victor Pody. siliconchip.com.au Sea). The UK plans to have ADS-B plus WAM implemented throughout the country by 2018. In addition, WAM and ADS-B have been deployed in the larger cities in Germany (Frankfurt, Munich and Berlin), in Portugal, Sweden, Bulgaria and Greece. ADS-B ground stations have also been deployed in Cyprus, Italy, Norway and the overseas territories of France. So as you can see, ADS-B is growing rapidly around the world and looks very much to be the aircraft navigation and surveillance technology for the future - or at least the next decade or two, until something even better is developed. Flightradar24.com We mentioned this amazing website at the start of this article. It’s been the cause of many a lost hour (oops, research!) following aircraft around the world. But as well as the deliberate “fuzziness” in the system, there are gaps. That’s because Flightradar24 relies on the altruism of individuals to receive ADS-B signals and relay them. There are about 500 privately owned ADS-B ground station receivers around the world, all of which relay the decoded ADS-B information back to Flightradar24’s server in Stockholm, Sweden via the internet. This allows the organisation to display all of the information on its website, in very close to real time – for monitoring free of charge by anyone, anywhere in the world. But as you might imagine, only 500 ground stations (which are as simple as an antenna, an ADSB-receiver and a broadband connection) would leave significant gaps in many countries – Australia included. When you look at Flightradar24 and note huge areas of, say, the African continent without a single plane, that’s not necessarily because there are no planes flying – it’s more likely that there are no ADS-B signals being received from that area. Flightradar24 covers about 90% of Europe and lesser amounts around the world. At the time of going to press, Flightradar24 were looking for operators in many areas around the world and specifically mention Western Australia and the north-western part of NSW. And they even offer free equipment (receiver and external S-mode plus siliconchip.com.au external GPS antennas and all cables and software) to tempt operators in some areas. Obviously, you’d need a good broadband connection and a healthy data allowance because your equipment sends ADS-B data back to Flightradar24 continually. As a reward, you also get access to Flightradar24 Premium (normally $2.99/month). As well as better displays, searches and filters, this allows you to use your Android or iPhone to identify an overhead flight simply by pointing its camera at it! For more information, visit www. flightradar24.com/free-ads-b-equipment We must admit, given the amazing number of aircraft being tracked in North America, that we were surprised that they were looking to fill so many on that continent. Perhaps it’s the sheer volume that’s beating them! So if you want to volunteer to receive ADS-B data, away you go: just log onto the URL above. But if you’re like the rest of us, just be amazed at the service that is provided for you! often anomalies in the identification of aircraft, their track, etc. Just what was that plane travelling from Miami to Ft Worth (USA) doing over Cowra in central NSW? Or another travelling from Darwin to Denpasar heading south near Alice Springs? No, we don’t quite understand why either. Could it be the data has been scrambled between the receiver and flightradar24? Or could it be that the receiver for some ports is below the horizon when the ’planes get to a certain altitude. We suspect that often only the origin and destination are fed into the system – intermediate ports don’t rate a mention, except that the ETA is often that of those intermediate ports. You will learn a lot – and question a lot. Like, for instance, why Jetstar and Qantas both have flights to the same destination (eg, Sydney-Melbourne) leaving within a few minutes of each other, when Jetstar is a Qantas subsidiary? (The same comments apply to Jetstar/Virgin – but they are in competition with each other). Tablets? One other point: while not exactly part of flightradar24.com, you’ll find your viewing pleasure greatly enhanced by listening to the tower at that airport. We Googled “air traffic control Sydney” and came up with quite a few websites – for example, drill down into www.liveatc.net and you’ll find many choices, such as Brisbane, Melbourne and Sydney centres, and in Sydney you can select North & East Approach, South & West Approach and Sydney Tower for runways 16L/34R and 16R/34L. We clicked on one option and ended up with www.bathurstscan.com/ frequency-lists/sydney-air-traffic-control-frequencies-and-stream/ which was very interesting indeed! It’s one thing to see the ’plane suddenly turn right onto heading 350° – it’s another to hear an air traffic controller tell that particular plane to turn right heading 350° – and then see it happen! OK, so that’s how ADS-B works and how you can view it on your computer. But what if you’d like to receive the actual ADS-B signal and display it? If you’d like to build your own ADSB receiver for next-to-nothing, see our article beginning on page 40. SC Yes, flightradar24.com is available for downloads on Android and iPads tablets – and the pro version gives you a lot more information for the really serious planespotter! Anomalies? The data is not perfect – there are Other sites We have concentrated on the website www.flightradar24.com, but it is not the only website providing flgiht tracking services. There are many others, some similar, others more specialised in their application (eg, tracking specific flights). But they’re all worth a look! Sites you could try (in no particular order!) include: www.flightwise.com www.planefinder.net www.flightaware.com www.webtrak.bksv.com www.flightstats.com www.radarvirtuel.com www.flightview.com www.flytecomm.com Want sound too? August 2013  17