Question for Ausi controllers

[framer]

Hi,
I've just read this


In December 2009, Air Services Australia commissioned the ADS-B Upper Airspace Project (UAP), providing ADS-B coverage across the whole continent. Since then, 29 duplicated ADS-B sites have been added, plus a further 14 sites in Tasmania which are associated with the now fully operational Tasman wide area multilateration (WAM) system. Aircraft avionics are being assessed and approved for operational use. ADS-B data from non-approved aircraft is filtered out at each site. Currently, over 1200 airframes are approved and receiving the operational and safety benefits of ADS-B services in Australia. Australia has also made ADS-B equipage mandatory for all aircraft (domestic and foreign) operating at or above FL290 as from December 2013.

what I'm wondering is, what difference does it make to how our position information is displayed to you? and what are the 'operational benefits' the 1200 airframes are enjoying?
Cheers

[le Pingouin]

ADS-B allows us to use the same separation standards as for radar instead of the far more restrictive procedural standards. You're more likely to get requested level changes & requested tracking.

[ameet0121]

Here we are using ADS-C and giving longitudnal separation of 50 miles over oceanic area. Can u elaborate over giving radar separation with ADS-B.

[le Pingouin]

ameet, you might find this of interest: http://www.airservicesaustralia.com/PROJECTSSERVICES/PROJECTS/ADSB/images/UAP_Flight_Ops.swf

For the controller there's little difference between using radar & ADS-B - both require line-of-sight so have similar range. We can use 5NM & vectors for both.

On screen the surveillance hierarchy is SSR, ADS-B, ADS-C so if more than one is available you only get the symbol for the highest available type.

When in both SSR & ADS-B coverage we get an indication in the label to show this so that when SSR coverage runs out you know whether you can still run the same surveillance standard or have to revert to procedural.

[Oceans13]

To provide Radar separation or effectively radar separation you need to be provided with continuous updates of position information. This is achieved with ADS B by the use of VHF. The difference with ADS C is that you only receive position information at a predetermined interval that is set in the original contract at logon or if you pass a compulsory reporting point. From memory, 27 min maximum for 50nm sep and 14 min for 30 nm sep. This system generally uses satellites (although VHF is also available if in range of a receiver) to rx/tx so it can be very expensive for the airlines if the position reports were to be every 6 seconds to match the update rate of radar.

[ameet0121]

Thanks. It was very useful. even the site suggested by Le was good. But if the renewal every 6 second is costly for ADS B then how this is useful as an alternate to RADAR. Also pl. specify can ADS B be used over oceans with no VHF link. Why it is only Air services Australia making full use of ADS-B where as other countries still continue to use Mode S.

[Oceans13]

ameet0121,

There is no cost involved with rx/tx using ADS B as it is VHF. The refresh rate I mentioned earlier is for radar, ADS B may in fact recieve many more updates per second. I am sure 1 of the guys presently using it can give the exact figure. The cost with ADS C comes from using the satellites for the RX/TX and charged to the airlines by the provider, either ARINC or SITA. ADS B is not used over the ocean unless in range of a ground station, it is purely a VHF system. ADS B is used in Australia in areas that were previously non radar to significantly improve the service to the airlines. It is cheaper to install and maintain than a standard radar system as it requires no moving parts and therefore brilliant for areas that are remote. The Mode S you ask about is a radar function using the transponder to deliver information about the aircraft, heading speed etc. So is used in areas with radar coverage. I hope that answers your questions. Good luck with your new system, ADS and CPDLC are amazing once you come to terms with how useful they can be.

[le Pingouin]

ADS-B & ADS-C - similar names, entirely different technologies.

ADS-B costs are about one tenth that for a radar site. Australia has many remote VHF radio outlets so there was little extra infrastructure required to fit ADS-B antennae & equipment.

In Australia it isn't being used to replace radar (we're updating to mode-S radars as well) but to provide surveillance coverage where none existed previously (most of the country). It's pretty "cutting edge" stuff as well so widespread adoption takes time.

You can't use it as a "drop in" replacement for radar as new aircraft equipment is required. Maybe some time in the future.... And there will always be a need for primary radar.

[framer]

what I'm wondering is, what difference does it make to how our position information is displayed to you? and what are the 'operational benefits' the 1200 airframes are enjoying?
Cheers

Thanks folks. I'm much wiser now. I'm picking the operational benefits to the 1200 Ausi airframes that have ADS-B is that they can be controlled in remote areas as if they were on radar as long as they are in range of a specifically equipped VHF repeater of some sort.And that there is no benefit to these same aircraft if they are over the ocean as they will be out of range of said VHF kit. Correct?

[Frequent SLF]

Just a minor quibble - ADS-B doesn't use VHF. ADS-B broadcasts on 1090MHz, the SSR frequency. In Australia and (I believe) parts of Indonesia, these broadcast signals are received by special equipment located on existing VHF sites and relayed back to the ATC system. This system has specific applicability in remote as opposed to oceanic airspace - something Australia has in abundance. (edited to correct SSR freq - What time of day is it again? http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/confused.gif)

[ameet0121]

Information I am gathering is much more than a book. Thanx ocean13 and Frequent SLF. A question comes to my mind is about accuracy. Practically can we give separation of 3 and 5 miles with ADS B. As u said acft is transmitting its position all around so is it possible that other acft too are getting the same display as ATC.

[le Pingouin]

ADS-B is currently approved & used for 5NM separation. I don't think 3NM has been approved yet but is being worked on - gathering data to confirm accuracy & reliability in real use.

Aircraft equipment can display ADS-B information for nearby aircraft, although what is displayed depends on the capabilities of the equipment. Controller needs & pilot needs aren't necessarily identical.

To clarify, the ADS-B equipment is mainly co-located with VHF radio outlets as power, data links & a tower are available.

[ameet0121]

Thanx for such informative discussion.

[Geoff Fairless]

Ameet - There is no requirement in Australia (yet) for 3nm separation using ADS-B because all of our busy TMAs are equipped with radar which is currently being upgraded to Mode S. Radar (SSR) is still the preferred separation sensor because it utilises transponders with which aircraft are almost universally equipped. We did however recently commission a Wide Area Multilateration (WAM) system in the Sydney Terminal Area to augment radar coverage and provide PRM to Sydney's close spaced parallel runways. It is approved for 3 nm separation and PRM. (The accuracy throughout the coverage area is generally 150 metres, reducing to 50 metres on long final and 30 metres on short final for PRM)

Another reason for not having 3 nm approval for ADS-B is that ADS-B equipment will only be mandatory above FL290(?) so the terminal areas will still be equipped with non-ADS aircraft. These can be tracked by radar and WAM because they track the transponder and do not require the transmission of position information.

The ideal situation would be for all aircraft to be ADS-B equipped so that ground surveillance becomes cheaper lowering the cost of ATC to aircraft owners. This has proven to be impossible even in Australia where arguably it would have been much easier than in more crowded continents. Fortunately WAM recievers can also recieve ADS-B (same 1090Mhz frequency) so the ones we are installing will still be useful later. By the way aircraft need ADS-B IN to recieve other aircraft ADS-B OUT transmissions. This is new and only just being incorporated in new aircraft.

Another use for ADS-B will be on the ground where we currently need about 15 multilateration receivers around an airport for A-SMGCS when probably 1 or 2 ADS-B receievers could do the same job.

[ameet0121]

As discussed ADS-B drives its position mainly from GPS+other equip like IRS, VOR DME etc. In case of war there are chances that GPS fails or some day satellites may fail. Then ADS-B may not work. Hence in future do we need to have both MLAT and ADS-B and of course primary radar or ADS-B alone is sufficient.