ADS-B in Australia (xhtml w3c 01/10)

AsA is progressively replacing ageing terminal area radars with the new Australian Mode S Terminal Area Radar (AMSTAR) equipment which utilises solid-state primary surveillance radar and Mode A/C and S capable SSR systems. The rollout commenced late 2008 with radars now operational at Coolangatta and Melbourne. New radars are also to be installed at Adelaide, Sydney, Cairns, Brisbane, Canberra, Darwin and Perth. The replacement program is expected to be completed by late 2011. ADS-B in Australia (xhtml w3c 01/10)

	ADS-B surveillance technology in Australia Rev. 9 — page content was last updated 30 October 2010 Edited November 2009 by RA-Aus member Dave Gardiner www.redlettuce.com.au
Flight Planning and Navigation

Content

13.1 ADS-B navigation and surveillance technology system concept
13.2 Aircraft and ground stations required
13.3 Airservices Australia's ADS-B system
13.4 Some options for airborne ADS-B avionics for recreational aircraft
13.5 Possible consequences for recreational aviation

13.1 ADS-B navigation and surveillance technology system concept

Satellite-based technologies — which promise a substantial change in airborne communication, navigation and surveillance [CNS] techniques — are nearing fruition. Among these is Automatic Dependent Surveillance – Broadcast [ADS-B].

ADS-B is an air traffic surveillance technology. A first stage ADS-B system ('ADS-B OUT' ) is operational, over most of Australia, for suitably equipped aircraft as part of the RADAR/ADS-B 'Surveillance Information Service'. The results from a prior trial show that ADS-B will contribute substantially to air traffic management [ATM] surveillance and separation capabilities — at a comparatively low cost for Airservices Australia [AsA]. It enables aircraft to be accurately tracked by air traffic services [ATS], without the need for secondary surveillance radar [SSR] except as a back-up system.

The concept for a total system is that all, or most, airborne aircraft automatically and continually (i.e. once or twice per second) squitter (i.e. broadcast) several digital data packets which together contain the aircraft's 24-bit address (the unique airframe identification), flight identification (call sign), GPS-derived latitude and longitude, barometric (or Mode C) altitude plus its three-dimensional velocity; i.e. rate of climb/descent, azimuth direction and speed. The Mode S transponder, currently used as the standard air-ground communication datalink in Traffic Collision Avoidance Systems [TCAS], will be used in ADS-B.

The United States Federal Aviation Administration [FAA] has decided that ADS-B transmission/data links in the USA will be via a Mode S 1090 MHz Extended Squitter [1090ES] surveillance link for air transport aircraft. (The term 'extended squitter' refers to the additional [112-bit] ADS-B data packet, which is part of the Mode S transponder data link standards.) For general aviation aircraft the FAA has specified a Universal Access Transceiver [UAT] surveillance link using 978 MHz in the DME band. UAT is a bi-directional data link system developed in the USA, specifically for ADS-B operation, so that general aviation aircraft with a UAT transceiver can also upload and display weather and other information, in addition to the ADS-B traffic information. AsA has opted for 1090ES for regular passenger transport aircraft; and possibly for general aviation later. In which case, probably no additional information facilities would be available to Australian general aviation and recreational aviation aircraft.

The European Union has issued a Notice of Proposed Rule for IFR aircraft above 5700 kg to be equipped with the Mode S Extended Squitter (ADS-B OUT) transponders.

(VHF Data Link [VDL mode 2 or 4], which operates in the civil aviation NAV/COM band, could provide a third type of data link capability.)

The data packets broadcast from aircraft are received by AsA ground stations, which feed the data to air traffic management [ATM] systems, providing more precise tracking than primary or secondary surveillance radars. The broadcast ADS-B packets are also received by all aircraft equipped with an ADS-B data receiver that are within range. The derived data provides a real-time cockpit display of traffic information, similar to the ground ATC systems except that the traffic is shown in relation to the receiving aircraft's intended track.

13.2 Aircraft and ground stations required

Airborne avionics

To achieve the full Airservices Australia ADS-B system concept, the onboard ADS-B avionics for general aviation and recreational aviation aircraft would have to include several functions or modes:

data transmission. This provides data broadcast capability so that positional data, provided by an inbuilt GPS engine and an altitude encoding altimeter or a pressure altitude encoder, is continually broadcast. This is known as 'ADS-B OUT' capability and all aircraft ADS-B units must have this minimum function. The accuracy of the broadcast data is dependent on the positional/navigational data from the GPS engine which, in turn, is dependent on the availability of GPS signals and the capability of the GPS software. A high-performance TSO* GPS engine is part of the system.

*Note: a 'TSO' or technical standard order is a 'minimum performance standard issued by the FAA for specified materials, parts, processes, and appliances used on civil aircraft'.

From 12 December 2013 ADS-B OUT units will be mandatory equipment for aircraft operating at or above FL290 in Australian airspace.
data reception. This refers to the capability to receive all data packets broadcast by all ADS-B OUT units within an appropriate range
data processing. This entails using the received data to provide a real-time plot of own and other aircrafts' tracks, speeds and altitudes; it is also known as a 'cockpit display of traffic information' [CDTI]. Alternatively, processing provides the data to a separate CDTI unit, which might be a handheld PDA. Data reception plus CDTI is known as 'ADS-B IN' capability, providing a pilot's own airborne surveillance and traffic alerting system — completely independent of ATC. ADS-B IN is the function that would benefit VFR recreational pilots, through enhanced situation awareness information; but probably only if an audible alert is provided, and the traffic information and own aircraft's position is overlaid on an accurate topographical chart navigation display; i.e. a GPS moving map with terrain database.

ADS-B IN capability is unlikely to be made mandatory for operations below FL180.

Ground station networks

If all aircraft in airspace above 5000 feet (for example) are fitted with ADS-B OUT avionics and a network of ground stations — capable of receiving the ADS-B OUT transmissions from the low-level aircraft — is ground or satellite linked to feed surveillance display screens at ATM centres, then a satellite surveillance network can be created on the 1090 MHz transponder reply frequency. Such ground stations, with their fixed omni-directional antennas, are much more cost-effective than radars to acquire, install and maintain; particularly so in remote areas. Possibly an ADS-B satellite network could replace the secondary surveillance radar [SSR] as the primary network. ADS-B also provides improvements in surveillance accuracy over that achievable by SSR with rotating directional antennas.

Other ADS-B ground stations and antenna systems have applications in terminal areas for surface movement control.

A fuller description of ADS-B is contained in an NPRM issued by the US FAA regarding their plans for ADS-B implementation.

13.3 Airservices Australia's ADS-B system

The upper airspace program

AsA states that ADS-B "is an air traffic surveillance technology that enables aircraft to be accurately tracked by air traffic controllers and other pilots without the need for conventional radar."

To date AsA has deployed 56 ADS-B ground stations at 28 sites across Australia which, combined with SSR, provide ATC surveillance capability over the entire continent above FL290 (29 000 feet ISA). From December 2013 carriage of ADS-B OUT avionics will be mandatory for aircraft operating at or above FL290.

These first 28 locations established an Australian ADS-B network for ground-based air traffic management; i.e. an ADS-B OUT system. These stations, each with a range up to 200 nm, are co-located at existing VHF communication relay sites and linked to surveillance displays at ATC centres, which allows Airservices Australia to provide an SSR-like traffic separation service across the current non-radar airways above FL290. Of course these same ground stations will also have the capacity for air traffic management at much lower altitudes — but shorter range, being line-of-sight dependent. About 1000 ADS-B equipped aircraft, including one trial ultralight (a Jabiru from David Eyre's Bundy Flying School), have been approved for operations in Australian airspace.

Currently in Australia the main Mode S transponder function is to allow aircraft equipped with Traffic Alert and Collision Avoidance Systems to 'talk' directly with each other, thereby enabling mutual resolution of potential traffic conflicts. Mode S can also provide faster, more accurate ATC surveillance, provided the ground radars are of the fast single pulse interrogation type. Many of the Australian SSRs are not monopulse radars and are being replaced.

The ADS-B OUT function is accomplished by upgrading an aircraft's existing Mode S transponder to 1090ES, and linking the navigation system and the transponder. The upper air space program won't affect recreational aviation in the short term, but the expected advances in avionics will eventually flow down to recreational aircraft.

The lower airspace program

"A major, longer term program designed to make ADS-B the primary means of ground to air and air to air surveillance in Australian enroute airspace. Includes installation of additional ADS-B ground stations to provide air traffic surveillance in airspace currently covered by enroute radar facilities. Intended to lead to the eventual decommissioning of a number of radar sites."

Initially an accelerated introduction of ADS-B surveillance into lower airspace was planned, but in the last quarter of 2008 it was agreed that a more gradual transition to satellite-based systems, harmonised with the North American and European transition plans, would be wiser. Airservices Australia will now "proceed with the replacement of its enroute radars and navaids as necessary to ensure the integrity of Australia's air traffic control system." (CASA's Notice of Final Rule Making – Transition to Satellite Technology for Navigation and Surveillance). The previously proposed cross-industry funding proposals will not go ahead.

"The timing and scope of future steps will be progressed through normal regulatory processes and will take into account ... outcomes of the Government's Aviation Policy Green Paper consultation."

So, it is probable that Australian recreational aviation and general aviation aircraft will be required to fit ADS-B OUT equipment for operations in controlled airspace (including Class E) and perhaps above 10 000 feet in Class G. Also perhaps for all operations within 20 nautical miles of non-towered aerodromes that have significant RPT movements; from the surface up to overlying controlled airspace. The preceding requirements are unlikely to be mandatory before 2020. There is no published schedule for the implementation of ADS-B IN.

13.4 Some options for airborne ADS-B avionics

Airservices Australia's ADS-B implementation team [ABIT] examined options for airborne units suitable for the low end of general aviation and suggested the following possibilities. The images below are based on images provided by Greg Dunstone, the ABIT program manager.

Option 1. Install an ADS-B OUT 1090ES transmitter (separate from any existing SSR transponder) with its own TSO'd GPS engine, external GPS antenna and an additional transmission antenna; probably bus-connected to avoid mutual interference. There must also be a connection to an altitude encoding altimeter or a blind encoder to supply pressure altitude. CASA has developed an Australian TSO to cover this unit.

Option 2. Add a low-cost, moving map navigation display (a PDA?) to the GPS engine of the preceding unit, using an NMEA 0183 serial port. There is no traffic surveillance — the display just utilises the positional data from the integral GPS and the aviation data stored in the PDA.

It may be a reasonable solution for light recreational aircraft if something like the AirNav VFR / OziExplorer topographic moving map display were utilised.

Option 3. This is a separate 1090ES ADS-B IN receiver connected to a more advanced moving map navigation display (a PDA?) deriving the position data from the ADS-B OUT GPS engine — probably using a NMEA 0183 serial port. The overlaid CDTI data is supplied by the 1090ES ADS-B IN unit. The difficulty with this solution is the complexity, the cost to the owner, the availability of a receiver-only ADS-B unit and the availability of software to add a surveillance overlay to the moving map navigation display. There are possibilities to use a common antenna with the ADS-B OUT'.

Option 4. Upgrade an existing Mode A/C transponder — or design a new unit — with 1090ES ADS-B OUT capability so that the existing aircraft Mode A/C transponder can be swapped out. The GPS could be either integrated or external. This is the simplest solution — the same as Microair's projected solution — and CASA has issued an Australian TSO to cover it.

This is a very good option for recreational aircraft using Class E but only if an RS-232 serial data port was provided for output of navigation data from an integrated GPS, in NMEA 0183 format, to something like an AirNav VFR or OziExplorer topographic moving map PDA display — or anything else that the aircraft owner may consider desirable at any time after the unit is installed.

Option 5. This is a low-power consumption, lower GPS integrity 1090ES ADS-B OUT unit for aircraft that will never require ATC separation, but which facilitates adequate situation awareness for other aircraft in VFR operations. It is a lower capability version of option 1 with no transponder: a 'cheap' solution that would satisfy a mandatory 'ADS-B OUT' capability with minimum cost — and minimum usefulness to the aircraft owner. But its utility would be increased if an RS-232 serial data port is provided for output of GPS navigational data.

13.5 Possible consequences for recreational aviation

It is possible that all aircraft currently required to carry a VHF radio will have to fit ADS-B OUT sometime after 2018 or 2020.

The ADS-B OUT only units are of no benefit to those VFR recreational aviators who never operate in the currently defined controlled airspace.

Individual perception of cost/benefit will vary greatly; one person's 'low cost' is another's 'arm and leg'; and that cost also includes panel installation, cabling, power supply, checking of electrical load, antennas, ongoing maintenance, and the requirement for biennial test and inspection of the altitude reporting facility by a CASA-approved technician. There is also the problem of shoe-horning it all into a very small airframe, of providing appropriate antenna positioning — and maybe a need to provide all antenna feed from a single bus.

The Australian land area is about 7.5 million km² and the airspace included from ground level to 5000 feet agl is about 12 million km³. Probably no more than 10% of the 15 000 registered aircraft are airborne at any time. So it is not surprising that the Australian history of recreational day VFR aircraft 'mid-airs' or 'near-misses' appears to be confined to the circuit area, to aircraft flying formation or to gliders sharing a lift source. In all these circumstances the likelihood of collision with another aircraft (or with the ground in a stall/spin incident) would seem to be increased if the VFR pilot's eyes are in the cockpit checking a small CDTI traffic display.

For those ultralight aircraft which are equipped to operate in Class E (only in daylight hours) under existing regulations, ADS-B OUT only units incorporating the Mode A/C transponder function (option 4) may be cost beneficial — if navigational use can be made of the integral GPS via an RS-232 serial port. However, about 75% of RA-Aus pilots carry hand-held GPS receivers mostly with moving map display and it is likely that every RA-Aus aircraft now regularly operating in CTA is equipped with GPS. By the time low-cost ADS-B IN, with CDTI on a terrain database is generally available those ultralights will already be equipped with off-the-shelf GPS moving maps with a very accurate terrain database. At that time, such units will be considerably cheaper than they are now.

This concludes the Flight Planning and Navigation Guide which I hope you have found useful. There are also two supplementary documents which should be read: "Operations at non-controlled airfields" and "Safety during take-off & landing".

If you have corrections or suggestions for improvement or expansion — please contact the author.

Groundschool – Flight Planning & Navigation Guide

| 9. Supplementary navigation techniques | 10. Global Positioning System | 11. Using the ADF |

| 12. Electronic planning & navigation | 13. ADS-B surveillance technology |

Supplementary documents

| Operations at non-controlled airfields | Safety during take-off & landing |

John Brandon 2004–2010 [contact information]

ADS-B surveillance technologyin Australia