Capstone

Gerry Caron wrote:

Mode-Select (Mode-S) was designed twenty years ago for a very specific set
of needs. It does that very well. It is an addressed communication system.
Trying to make it do something for which it wasn't designed could compromise
the system or at best add a lot of expense and complexity.

UAT was created about 8 years ago specifically to support ADS-B, TIS-B, and
FIS-B. Note the "-B" in all the systems -- that stands for broadcast. UAT
is a non-addressed broadcast system. Basically it's a half-duplex radio
modem. When you transmit, you have no ability to determine who is
receiving. Likewise, in receive, you'll receive anybody within range.


mode-s ("squitter") is also designed with these properties. The proposal to
add ads-b to mode-s originally had the mode-s transmitter start transmitting
asyncronously if the unit was not swept within a given period of time. Ie.,
lacking radar, the unit would switch to true ads-b mode.


Airlines have Mode-S because it's a required part of a TCAS system, which is
mandated. TCAS will not be going away. ADS-B may augment TCAS, but it
won't replace it. Adding ADS-B to the Mode-S system is the most
cost-efficient route if you already have the Mode-S/TCAS equipment.

I would say that at this state of the technology, that mode-s is going to be
the most cost effective for everyone. UAT is brand new, untried technology.
mode-s already has a lot of units and support. UAT is simply going to cost
more, for a while.

Having a defacto requirement that you need both mode-s and UAT on a light
airplane is certainly not going to help costs for light airplanes. And it
will be the defacto requirement once pilots find out they really should
have both to prevent being run over by a transport aircraft under all
conditions, including no radar and radar shadows.


Major point here. The ADS-B repeater/translator is NOT radar based. It is
a 1090MHz receiver and a UAT receiver to "collect" ADS-B broadcsts from
aircraft in the vicinity. The data is then broadcast out on both 1090 MHz
and UAT (this broadcast is called TIS-B -- this is not the TIS you currently
have.) These are relatively cheap (a couple orders of magnitude cheaper
than a radar) autonomous ground stations that can be stuck pretty much
anywhere, including places where there is no radar coverage. This is
exactly what they did in Alaska for Capstone.

Still means that you need a ground based translator to get from light airplanes
to transport aircraft. ADS-b's best feature was that it didn't need to depend
on ground stations. That ground station adds a new point of failure to the
system, as well as being a fickle one. I don't care how high tech digital
you get, that signal is not going to go through a mountain, whereas I have
never heard of a midair collision where the colliding aircraft went through
a mountain, ie., generally you have line of sight for an aircraft you are
colliding with.



o Light airplanes unlucky enough to have high altitude capability would
need both mode-s and UAT. This would also apply to a huge number of
jets and even heavy aircraft, since there are a lot of light jets and
passenger aircraft servicing smaller, non-radar fields.


No. You can pick one, or neither, or both. While you may need a basic
Mode-S transponder for some high altitude airspace (RVSM), that does not
mean you have to have a 1090ES ADS-B system.

When ADS-B is required on class A airspace, then high altitude light planes
are going to need it as well. Unless you can think of a class A requirement
that was excepted for light aircraft ?


A fine point here. Your GTX330 is a long way from a 1090ES ADS-B system.
It currently provides only elementary surveillance support. It would
require an upgrade to support full ADS-B broadcast. Once you did that, you
could provide ADS-B broadcasts, but you'd still have to get a 1090 MHz
receiver to be able to receive ADS-B or TIB-B over 1090. (Your TIS data
comes up from the ground radar on 1030 MHz using the Mode-S comm-b
protocol.) Adding that receiver will not be cheap. The receiver and
transponder upgrade will likely cost as much or more than a UAT.

Gerry



Good point (didn't know that), but it isn't going to change the fact that you
will need both systems. No, the airlines are not going to care, they simply
want uncontrolled airplanes out of their way no matter what. But as the
ramifications of having two "separate but equal" ADS-B systems work in,
its going to be understood that you better have both systems to be really
safe.

I disagree that it had to be this way. The FAA cannot even create one standard
for a brand new system ? No, what they did is throw a special interest party,
and give everyone what they wanted (even though they don't work together).

It stinks. Sorry, it just does.

"We like standards. In fact, we like them so much we think everyone should
have their own..."