ADS-B: Am I missing something?

[gismo]

...which makes me chuckle, since I'll be using 1090ES with my upgraded GTX330... (1090ES is basically mode S on steroids.)

The GTX330 does transmits aircraft position via 1090ES (which will make it visible to big iron) but AFaIK it will not receive and process 1090ES position info directly from other aircraft and instead requires a TIS-B ground station for that. If this is true, you will still need a UAT in order to display other GA traffic (equipped with UAT) when outside the TIS-B coverage and won't see other 1090ES traffic there either.

At least the big guys will be able to see you so you can be absolutely certain they won't run you over .

From what I've read, full blown 1090ES (can see other 1090ES traffic without ground support but cannot see UAT traffic independently) is only available as part of a complete big iron FMS package costing about half a million bucks. OTOH I see no technical reason why such a capability can't be developed for GA with a "reasonable" price tag of 10-15k.

 

[gismo]

The original NPRM says that all of the ADS-B ground stations will perform this conversion from one format to another, and that they expect the same airspace coverage as current radar (including Center radar). So there will be a huge area of ADS-B coverage - orders of magnitude greater than current TIS. But you are correct, there will still be pretty big holes and the system is vulnerable to ground equipment failure.

My preference would be to skip this silly (and expensive) ground repeater stuff and install a receiver in my aircraft which can pick up ADS-B on both frequencies. I'd happily replace my transponder and TCAD with that once ADS-B is widely adopted.

Thanks for clearing that up Joe, it does make things a lot better than I thought although like you, I still can't see why they can't come up with a totally compatible interoperative concept.

GA also needs to be aware of the strategic problem with dual frequencies: All the airlines will be on one frequency, GA will be on the other. The infrastructure for the second frequency as well as the repeaters to translate between frequencies are potentially billable directly to GA. This will be huge ammunition in favor of user fees.

I hope it works out that way but I'm not betting real money on it. Both technical standards and rules are still in flux. Given the saturation which is already occurring on the 1090 band it's possible one may not be allowed to install 1090ES unless one operates in the flight levels

It also seems like there may well be a saturation problem on the UAT side when a large number of UAT equipped airplanes are operating in the same area. I hope the system architects have that part worked out properly.

One other issue I haven't seen addressed is that since this whole house of cards is totally dependent on each airplane's ability to determine it's own position, any GPS outage such as a major solar event, DOD testing, and illicit jamming would probably mean grounding all GA or at least eliminating all IFR GA unless someone comes out with an inexpensive inertial reference system that works in light airplanes (extremely unlikely). This would exacerbate the related navigational issue we will face when the FAA pulls the plug on the VOR system since we will lose both navigation and ATC guidance at the same time.

 

[Walt]

I think we will be using our transponders for many years. ATC will have a dual parallel system (ADS-B and radar) in most areas. GA will have an unreliable traffic alert system as we do now. Looks like lots of money to be spent to comply with regulations, but no improvement in safety. (sigh)

 

[Joe B]

One other issue I haven't seen addressed is that since this whole house of cards is totally dependent on each airplane's ability to determine it's own position, any GPS outage such as a major solar event, DOD testing, and illicit jamming would probably mean grounding all GA or at least eliminating all IFR GA unless someone comes out with an inexpensive inertial reference system that works in light airplanes (extremely unlikely). This would exacerbate the related navigational issue we will face when the FAA pulls the plug on the VOR system since we will lose both navigation and ATC guidance at the same time.

That's why DHS started building out eLORAN earlier this year at the request of numerous user communities including aviation. We don't have aircraft receivers for it yet but when they come around they should make a nifty backup for driving ADS-B when GPS goes TU. eLORAN won't have the spatial resolution of WAAS GPS - but the degraded performance should allow a GPS-less situation to be a manageble concern instead of an emergency.

From what I've read, full blown 1090ES (can see other 1090ES traffic without ground support but cannot see UAT traffic independently) is only available as part of a complete big iron FMS package costing about half a million bucks. OTOH I see no technical reason why such a capability can't be developed for GA with a "reasonable" price tag of 10-15k.

Agree completely with that. Development of ADS-B trancievers is frozen right now while all manufacturers wait for the technical specifications to settle down. No ADS-B device currently available is compatible with the proposed rule and their makers don't want to get burned twice. Once there's a final rule we should be off to the races and there should be some healthy competition in the market.