ACAS and other Q's

[Tor]

Could someone please explain me the difference between TCAS and ACAS?

Also, ACARS is based on an air to ground datalink? How does it work with FANS?

Thanks

Tor

[10W]

ACAS is the system specification for equipment designed to provide a last resort method of avoiding mid air collisions.

TCAS is the only commercially available equipment which currently meets the specification.

You can get a lot of info on ACAS (from the European point of view) here:

http://www.eurocontrol.be/projects/eatchip/acas/


FANS is a datalink application which provides Automatic Dependent Surveillance (e.g POS reports) and/or Controller/Pilot Datalink Clearances (CPDLC). To do this it either uses Satellite Aircom or VHF Aircom links. ACARS is one method of sending messages via the VHF Aircom route.

The ACARS messages are sent to/from the aircraft and the ATC unit via a service provider, e.g. ARINC or SITA. You shoud be able to find more on those companies websites.

http://www.arinc.com/Products_Services/GLOBALink/cads.html

http://www.sita.com/Default.htm?/airlines/ag_fans1a.html



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10 West
UK ATC'er
[email protected]

[Tor]

Thanks for the links.

So TCAS is ACAS?

[10W]

Hi Tor,

TCAS provides a system to meet ACAS requirements. So could something else if it was invented and met the specs. It's just there's nothing else around at the moment.

Having said that, US cargo operators are trialling an Automatic Dependent Surveillance - Broadcast (ADS-B) system with a view to providing an alternative to TCAS.



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10 West
UK ATC'er
[email protected]

[411A]

"TOR": You must understand that the Europeans could not stand to use USA technology. So, they adopted TCAS (renamed ACAS) because they could not/would not admit that it actually worked. That is why it was so late in arriving in Europe. Same with GPS. Question; how many GPS approaches are approved in Europe. Answer: not many because..."it was not invented here."

[RevStar]

Tor,

Yes, TCAS is ACAS (its just the 'brand name' if you like)... the reason the European's haven't used it mandatorily up to now, was that the US bought it in without proper certification/trials etc (in the European's opinion). The original system was thought to have too many glitches. Since then, version 6.04a has come out in the States, and Europe has mandated ACAS version 7 (enhanced, so that there are less false TAs and RAs) for implementation on all commercial a/c in the near future (determined by weight).

411A, behave yourself :-)... I don't know about GPS apps, but there were plenty of sensible reasons at the time for not bringing in TCAS. Saying that, the loyalty to products developed in your own region is prevalent both sides of the Atlantic! That attitude is slowly disappearing, but it has been a problem. There are now a lot of joint FAA/Eurocontrol teams, looking to implement products/concepts on both sides of the pond.

10W, ASAS (Automatic Separation Assurance System), using ADS-B, will NOT be a replacement for TCAS. Although the Americans are trialing a conflict detection and resolution system within this system (under their SafeFlight 21 programme), it is not thought that the 'safety net' of TCAS will be lost. In fact, it is a large bone of contention as to how much duality there can be between the two systems (in terms of processing data, and displaying it).

For more info on the above, there's tons of websites around including: http://www.faa.gov/safeflight21/ http://www.ads-b.com/Content/index.htm

Also, a quick note on ACARS/FANS. As 10W said, ACARS is one version of an air-ground datalink, currently used by the airlines (for ops, amongst other things). However, the ACARS system is not especially robust... therefore, an Aeronautical Telecommunications Netowrk (ATN) is in development to provide better control of message routing (also security and reliability is said to be improved). This is only the comms part of the FANS package - surveillance functions (ADS-Contract) and navigation functions (GPS) are included as well.

RS.

[This message has been edited by RevStar (edited 07 November 2000).]

[10W]

411A

With respect, the comment about Europe and TCAs is b*ll*cks. To mandate any equipment in Europe, there is a 7 year lead in time between advising industry and the legislation being passed. That's the law. So given that, Europe obviously accepted the principle of ACAS at least 7 years ago.

Same with the requirements for RNAV. In that case, they did however rush through the acceptance of GPS as a means of accomplishing RNAV (or more precisely BRNAV) under intense political pressure from operators.

I also think you'll find that until very recently there was no guarantee of service provision of GPS by the US military, or that it would continue to be provided for any specific time period to civil users. So why would any authority lead operators down a path to equip with a piece of kit with no guarantees ?? Common sense says that they wouldn't. I'd love to see the beancounters accept the cost benefit analysis for that kind of situation !! As it now stands, there are assurances so I'm sure that things will gather pace in Europe, but in accordance with the laws and processes that are in place.

RevStar

10W, ASAS (Automatic Separation Assurance System), using ADS-B, will NOT be a replacement for TCAS.

Erm I didn't think I said it would replace it, I said it was an alternative. Subtle difference ;) It is more likely to appeal to those operators who can use it for other things but are not mandated to carry ACAS, e.g. freight dogs.

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10 West
UK ATC'er
[email protected]

[RevStar]

10W,

Sorry, I see what you're saying now. However, the point still stands... an alternative to a system would generally perform the same function as that system (therefore being used in lieu of said system). ACAS and ADS-B are two separate systems, designed to carry out to different functions, and therefore cannot be used as alternatives. The CAA (Cargo Airlines) are looking at ADS-B for conflict detection, but it will not be such a 'last-minute resort' system as TCAS/ACAS (i.e. ranges of less than 7NM).

[10W]

RevStar

Yep I agree. But I'm sure that some in the industry will be looking to see if cockpit technology can be developed using other applications (e.g. ADS-B) to provide something which can meet the ACAS requirement. In some ways developing such a system could actually enhance ACAS since it would be able to build in medium term conflict detection algorythms (10 minutes or so out) and in-cockpit Airborne Situation Displays. That way pilots might be able to be told to avoid specific aircraft, and the systems on board co-ordinate a plan in a timely manner (as opposed to TCAS' last gasp instructions). A sort of 'electronic' VFR I guess ?

Hey, we could call it something snazzy like 'Free Flight' ?? :)

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10 West
UK ATC'er
[email protected]

[RevStar]

10W,

"Yep I agree. But I'm sure that some in the industry will be looking to see if cockpit technology can be developed using other applications (e.g. ADS-B) to provide something which can meet the ACAS requirement."

Surely not another example of commercial benefits neglecting safety... (!).
The new CD&R (conflict detection & resolution - I hate all these damn acronyms!) is more of a strategic tool than a tactical one. The problem comes when airlines say, "Hey, why can't we integrate the two.".

The electronic VFR - work is progressing on this both sides of the Atlantic (and elsewhere) - the first step is using the CDTI as an aid to visual acquisition - catchily(!) known as 'Enhanced Visual Acquisition of other traffic for see-and-avoid'. What's interesting is whether many of these procedures will require HUDs to be used effectively (from a human factors point of view)... any pilots flying with HUDs care to comment on their effectiveness? Or any pilots care to comment on their views on these new procedures (which WILL come in, eventually - circa 2008 is proposed for Europe at the mo)?

RS.

[Blacksheep]

10W,

"in Europe, there is a 7 year lead in time between advising industry and the legislation being passed. That's the law."

Hmmm....

8.33 KHz channel spacing? ACAS? Automatically deployed Emergency Locator Beacon?

8.33 KHz channel spacing was rushed through before equipment was designed and certified. As a result there were a number of problems with obtaining upgraded transceivers in time to meet the deadline. "ACAS" requires upgrading TCAS software to version 7.0. Not only was version 7.0 not available but Boeing has flatly refused to provide retrofit service bulletins for their aircraft so we are forced to install modified TCAS Processors using STCs obtained from the equipment vendors. Honeywell have just scraped their STC (for B767s) through in the nick of time. We are still not certain that all TCAS Processors can be rolled over through the workshops for modification within the deadline. The JAA tried to mandate installation of an emergency locator beacon that is not only automatically activated but also automatically ejected from the aircraft on impact. They had to back down and postpone this requirement indefinitely as no such piece of equipment is even in the design stage yet.

No, I don't think that seven years notice is the law. We engineers only wish it were!

**********************************
Through difficulties to the cinema

[10W]

I am led to believe that the 7 year notice is an ECAC 'rule'.

For 8.33, that was truncated I agree. But the agreement to put it in place was ratified at the EUR RAN meeting which took place in Vienna 1994. The implementation was in October 1999. So, OK it wasn't 7 years, but industry had at least 5 to get their act together ;)

ACAS is another case in point. Agreed in 1995 that it should come in in 2000. 5 years again for industry to do something. Hey, maybe my 7 year is a mistake and it should only read 5 !! ;)

RVSM, notified in 1994, coming in in 2002.

RNAV carraige, agreed in 1990, to come in in 1998. Yet we still have people flogging about with exemptions http://www.pprune.org/ubb/NonCGI/frown.gif

Can't comment on the ELT type of thing as I have no knowledge of that programme. But the cynic in me says that 'industry' promises to the authorities that all the bits of kit for these programmes are no problem and that the timescales can be met. They then go off and think, mmmm, 5/7 years away, let's not worry about that just now. The operators say, mmmm, 5/7 years away. I'll pop down the local avionics shop six months before and get it cheaper and to a better spec. End result is manufacturers way behind the drag curve and operators unable to get their hands on kit which has literally just come into production and with the availability of hens teeeth.

And as for ATC systems....... :)



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10 West
UK ATC'er
[email protected]

[RATBOY]

A little further back on the thread Rev Star pased I question I have had forming. When the CDTI is put in the cockpit it takes x amount of real estate, then somebody puts in an ACARS terminal, and a GPS or two, then the moving map display, then the xxx. It doesn't take long for somebody to say (a) shouldn't we put them together because there is only a finite amount of cockpit realestate (except in 747s)and (b) what are the crew going to do with all these gee whiz boxes, displays, etc.

Is anyone working on this stuff?

As far as the ELT stuff goes just had a little visit with a Civil Air Patrol ground search/rescue guy who has been hunting ELTs (the VHF 121.5 variety) for 20 or so years and says the new UHF FM beacons are great. They send a data burst every minute or so that identifies who is sending and if there is a link to the navigation system (or an attached GPS card) tells everyone where it thinks it is. Makes it much easier to find and also is more easily heard with orders of magnitude greater position accuracy by the satellites, let alone the ground pounders with hand held receivers. If people can be persuaded to install them and use them it will save more than a few lives, including the ones of the people that go and search for you when you crash.

[RevStar]

RATBOY

Is anyone working on this stuff?

The main people working on the integration of CDTI and ACAS are SafeFlight 21 - url above. Several different versions of an integrated display have been produced, and were trialed last month. The cargo airlines (UPS/AT especially) have developed a TCAS-like conflict avoidance algorithm (based on ACAS II Change 7) and incorporated it into the CDTI... so as 10W said in an earlier post, people within the industry are trying to save room. Whether anything else could be integrated (for instance, the CDTI control panel within the FMS) remains to be seen.

As for what the crew are going to do with the toys, it depends whether procedures have been already set down b4 implementation. One problem the industry has is 'technology exhibitionism'... perhaps they should look at whether its nice to have, or whether its essential? One thought going round at the mo is that the customers (airlines) should decide what technology is needed, then providers respond - that way procedures get defined early on. :)

10W

It seems to me that the biggest problem for developing new technologies is to prove the benefits to the operators (airlines)... if there is no clear discernible commercial benefit, they will be very slow to equip. They are the customers, and so drive what is equipped. Interesting to note that RVSM and 8.33 KHz both have clear business benefits. ELT is more of a pure safety matter - no commercial benefit as such.

So call me a cynic! ;)

[This message has been edited by RevStar (edited 08 November 2000).]

[RATBOY]

ACAS using some other technology than TCAS/ATCBI has been proposed and from a technology point of view appears feasible. Question is as I understand TCAS to get the ultimate in service from it the other aircraft must be TCAS equiped or Mode S xponder equiped. A regular ATCBI transponder is okay but doesn't get the ultimate service. So if some people are automatic dependent surveillance broadcast (ADS-B) plus xponder and others are TCAS the overall benefits to all will be less. Of course UPS/AT is an avionics manufacturer and has it's own point of view on whether more better boxes are the solution. (of course they are!!)

The question of which came first, the procedures or the technology (or the requirement, for that matter) is fundamental. Setting aside the formal requirements identification stuff it seems to me that the procedures and the technology evolve hand in hand. The system we have today is based upon VHF am radio communications and navaids and seems to have come almost as far as it can and it is now time for a quantum leap in technology and procedures. I think everyone could come to consensus on what future procedures and technology should be, but getting there from here is the hard part. And doing it while competing with other investments and opportunity costs adds a further complication.

To reduce the overall risk for everyone the procedures will have to evolve substantially quicker than they have in the past taking their own sweet time. Possibly a way to evolve quicker is an industry/regulator/service provider joint trials activity/virtual organization to use simulators and real crews/controllers/engineers to try things out and evolve procedures faster than would otherwise be the case. It would be much easier to try out what may be a high payoff procedure development in the simulator with no metal or people riding on the outcome than it would be to try it out for the first time in the real world.