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Scott Dunham (RDU)
Top Gun


Reged: 04/29/04
Posts: 6470
Loc: Chapel Hill, NC
Re: FAA Reauthorization Bill [Re: Joe Budge (W29)]
      #285560 - 03/29/10 09:27 PM

Your UAR isn't going to have a whole lot to listen to from other airplanes if they don't buy UAT's, either.

The dual-band ADS-B concept wasn't driven so much by saturation on the mode S datalink (although that's an issue) as it was by people/companies who wanted to stick with what they already had. As previously noted, mode S is a crummy datalink compared to UAT. IMHO, in a data-driven world, it is remarkably shortsighted to intentionally limit future aviation data services to what can be carried by mode S. So, the FAA decided to support both - but not because it was a great technical idea. They just caved to pressure from mode S users who don't want to upgrade, while allowing others to progress. For the argument you're making, I guess that should seem reasonable. I think supporting surveillance, collision avoidance, and weather IS a defined benefit - and doing it in a flexible way with room to grow seemes to me to be a lot better than trying to cram more stuff onto the mode S channel when it can barely handle what's there now.

>> (There is no difference in the data transmitted from the aircraft on Mode S ES than on UAT.)

Now, maybe not. How long would you think that a reasonable limitation? As long as both systems are in use, they do need to play nice together, so to some extent Mode S will serve as lowest common denominator for data transfer.

I don't want anybody to waste money, either - but mode S vs UAT strikes me as about like arguing dial-up vs FIOS. I don't know too many people who regret upgrading, and I'm happy that the FCC didn't settle on 56K as the standard for the next 30 years.


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Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
FAA Reauthorization Bill [Re: Scott Dunham (RDU)]
      #285589 - 03/30/10 12:50 AM

Scott -- Sure, XM could crump or go bankrupt. But so long as it's there,
it's more to my liking than what the fed is offering. What makes the most
sense is for this additional service to be space-based, perhaps on a model
like DUAT, private vendors with government contracts, that may ensure
continuity over the long haul.

Unfortunately, that lowest common denominator approach isn't working in the
marketplace.

--------------------
www.scottdyercfi.com


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Joe Budge (W29)
Top Gun


Reged: 04/30/04
Posts: 7423
Re: FAA Reauthorization Bill [Re: Scott Dunham (RDU)]
      #285600 - 03/30/10 03:05 AM

You make a very good point about the data communication architecture. Unfortunately, that isn't how the FAA is selling or implementing ADS-B. Trying to boil this down to essentials, here's how I see it:

- The label of ADS-B and the technology's stated purpose is to allow the FAA to replace their surveillance system with something cheaper. Fine. I'm willing to go along with that, within limits.

- The only thing necessary to implement the above objective is ADS-B Out. Everything about ADS-B In is optional, designed to serve some greater purpose.

- If ADS-B Out will work reliably on Mode S, that is clearly the most economical solution for the user community. (And if it's an "either-or" question, it's an economic "don't care" for the FAA. As is, the FAA is spending for both.) Given a choice, the user community will choose Mode S based on economics.

- In supporting the "two-band" solution, the FAA is implicitly agreeing that ADS-B Out will work reliably on Mode S. (If it won't work reliably on Mode S there are a whole host of embedded issues that boil down to your Chairman calling up the Administrator and asking "WTF do you think you're doing?")

- So the only reason to mess around with UAT's is to support some greater purpose called ADS-B In that has nothing to do with what ADS-B, the technology, actually means.

- As you've gathered by now, I don't see a present value in the collision avoidance and weather services which the FAA proposes and someone has lobbied to mandate for ADS-B In. Those problems have already been solved in other ways. IMO we don't need the FAA to solve them again. "Waste" is the word that comes to mind. I have a bunch of other, less-polite words for the FAA's practice of trying to make ADS-B In and Out seem inseparable in order to sell the program. In short: I think the FAA should be spending its resources and mine on problems that haven't been solved, not on ones that have.

- I hear you loud and clear on the data comm technology. When there is a critical service which cannot function without it, that will be the time to sell us on the new technology. We haven't seen that point yet. This is a technology in search of a problem.

Regards,
Joe


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Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
FAA Reauthorization Bill [Re: Joe Budge (W29)]
      #285616 - 03/30/10 11:23 AM

Joe -- A'men, brother. You've nicely described how I've come to view this
stuff, more eloquently and concisely than I would have. And, it's not just
the FAA that is to blame for the "IN" mess...I think AOPA really screwed up
on this, too.

--------------------
www.scottdyercfi.com


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Sean Franklin
Top Gun


Reged: 08/15/04
Posts: 2566
Loc: Eureka Springs, Arkansas
Re: FAA Reauthorization Bill [Re: Joe Budge (W29)]
      #285640 - 03/30/10 03:15 PM

Quote:

I don't see a present value in the collision avoidance and weather services which the FAA proposes and someone has lobbied to mandate for ADS-B In.



Joe, I agree with you on weather. However if at some point in the future there will be airplanes buzzing around with UAT's but no transponders, traffic avoidance becomes a big issue. If ADS-B becomes mandatory, at what point will transponders become optional?

--------------------
Eureka Springs, Arkansas


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Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
FAA Reauthorization Bill [Re: Sean Franklin]
      #285641 - 03/30/10 03:24 PM

Sean -- I don't think that they will become optional in the foreseeable
future, as the air carriers rely on the transponders for the TCAS system.

--------------------
www.scottdyercfi.com


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Joe Budge (W29)
Top Gun


Reged: 04/30/04
Posts: 7423
Re: FAA Reauthorization Bill [Re: Sean Franklin]
      #285668 - 03/30/10 06:00 PM

Quote:

If ADS-B becomes mandatory, at what point will transponders become optional?




The key to this question lies with what the FAA decides to do with TCAS. In order for transpoders to become optional, the FAA would have to mandate that *all* TCAS systems be upgraded to accept traffic data from both transponders and ADS-B UATs. This would have to happen by some specific date, and would have to apply to all TCAS-equipped aircraft in our airspace, including foreign ones. Aircraft which were not ambidexterous, so to speak, would have a TCAS that only worked some of the time - not a good thing. Such a mandate would encounter strong opposition from the airlines - who are already howling about the cost of putting ADS-B in their aircraft. I believe our relationship with ICAO is governed by treaty so there'd be some thrashing on the diplomatic front as well.

In addition there's a technical hurdle: if your aircraft has both a transponder and an ADS-B UAT, the TCAS-equipped aircraft will see two traffic returns relatively close together. Are they one aircraft or two? It's easy to answer that question with ADS-B and regular Mode S because the aircraft identifies itself in its returns. Impossible to tell if the target aircraft only has Mode C. So I suspect a move to ambidexterous TCAS would also force a move to Mode S for everyone who keeps a transponder.

Under present circumstances I don't think any of this will come about for a long time. If we find out that piggybacking ADS-B on top of Mode S doesn't really work after all, then it'll be a whole different ball game.

Regards,
Joe

Edited by Joe Budge (W29) (03/30/10 06:02 PM)


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