On 8/9/2010 3:44 PM, Darryl Ramm wrote:
On Aug 9, 9:23 am, wrote:
On Aug 9, 7:12 am, wrote:
[snip]
Mike and Renny,
a good discussion of the macro view of FLARM and ADS-B. Another view
is more personal, for example in my situation- I fly a lot of ridge
and mountain in a very narrow altitude band and a lot of clouds. There
is not a lot of power traffic in those conditions. I have a
transponder but I don't see the Transmit light going off very often
and I suspect I am not getting very many radar paints down in the
rocks and trees where I like to fly. My greatest risk is from the six
other gliders I share the area with, which do not have transponders
and will never get them at the current costs; in fairness my threat to
them is even higher as I am a low hour pilot. FLARM would go a long
way to reducing the risks and at a reasonable cost; PowerFlarm would
be my choice as it would also provide protection from ADS-B and
transponder equipped threats, but at twice the cost the installed base
in my situation would be very much reduced and I stand a better chance
of talking my potentially deadly friends into investing in FLARM. 2020
is not soon enough. It is not soon enough for the pilots killed on a
regular basis at contests, which we seem to simply accept as an
unavoidable risk.

With that in mind Mike's statement that FLARM isn't of use (for me)
would not be correct. In 2004 my club lost two gliders and a pilot in
a collision that would not have happens if they had had FLARM. How do
you calculate that cost?

Brian

Brian& folks

Sorry to hog the thread but I want to make sure that key technical
facts are nailed down.

Brian wrote...

PowerFlarm would be my choice as it would also provide protection from ADS-B and
transponder equipped threats, ...

PowerFLARM or any other 1090ES receiver in the USA will "see" other
ADS-B data-out equipped traffic if and only if one or more of the
following is true

1. ADS-B Direct. That other traffic is transmitting ADS-B data-out on
the same physical link layer (i.e. a Mode S transponder with 1090ES
data-out).

or 2. ADS-R (ADS-B Relay). That other traffic is transmitting on the
other physical link layer (i.e. a UAT transmitter or transceiver)
*and* your aircraft is correctly transmitting ADS-B data-out that
describes the aircraft location and ADS-B receiver configuration (aka
the "capability code" bits)
*and* both aircraft are within range of one or more ADS-B ground
stations
*and* the aircraft are within the ADS-R "service volume" (or "threat
cylinder" in my terminology) of what I beleive is +/- 3,500' and 15
nautical miles of each other

---

If you don't meet *all* the requirments in #2 above your ADS-B
receiver may still see other traffic, especially traffic near other
ADS-B data-out equipped aircraft, but there is no gaurentee that you
will see all traffic near you. The PowerFLARM is not an ADS-B
transmitter so you will need a Mode S transponder with 1090ES data-out
or a UAT transmitter/receiver to make the ADS-B traffic part of the
PowerFLARM work properly. My expectation is given that ADS-B is a damn
confusing mess that at least for the next several years pilots in the
USA who buy a PowerFLARM will likely mostly do so for the flarm-flarm
and PCAS capability, and if they also see 1090ES data-out aircraft
(esp. airliners and fast jets) that great, but I do worry that many
pilots won't understand they will not properly see say GA UAT equipped
traffic without an ADS-B transmitter.

---

The PowerFLARM has PCAS capability so is the threat aircraft
transponder is being interrogated the PowerFLARM should be able to
warn you of a threat and its relative altitude but it won't have
direction information. The nice thing about this is many of us have
positive experiences with Zaon MRX units where there seems to be good
interrogation even outside of standard SSR coverage (via TCAS and TCAD
interrogators etc). However if the concern is about ridges and other
fairly obscured sites then there just may not be enough interrogations
to make a transponder useful for a PCAS (PowerFLARM or Zaon MRX etc.)
unit to detect anything. Of course if the threat aircraft has a Mode S
1090ES data-out transponder then the PowerFLARM will directly the ADS-
B data from the transponder.

PowerFLARM will also have ADS-B TIS-B support but it is not initially
shipping with this enabled. TIS-B is the relay of other aircraft SSR
position data to ADS-B equipped aircraft so they can "see" transponder
only equipped traffic.

TIS-B (ADS-B Traffic Information System) requires that the other
traffic has a Mode C or S transponder
*and* is within coverage of a traditional SSR radar (or
multilateration system). i.e. think airspace where you have ATC radar
coverage today.
*and* your aircraft is correctly transmitting ADS-B data-out that
describes the aircraft location and ADS-B receiver configuration (aka
the "capability code" bits)
*and* your aircraft is within range of an ADS-B ground station
*and* the threat aircraft is within the TIS-B "service volume" (or
"threat cylinder" in my terminology) of your aircraft - I believe that
is is +/- 3,500' and 15 nautical miles.

---

Since Brian mentioned ridges as a scenario, a potential concern there
is that you may be frequently outside of ADS-B ground coverage and
therefore ADS-R services may be unreliable or not work at all. So even
if all the gliders are properly equipped a 1090ES ADS-B equipped
glider just won't "see" a UAT equipped glider an visa versa. Although
ADS-B ground station coverage compared to traditional SSR radar is
going to be impressive, including at many locations down to very low
altitudes, ADS-B as deployed in the USA just is not designed to deal
with scenarios like ridge soaring. To deal reliably with this glider-
on-glider ridge scenario all gliders in that area would need to adopt
a single physical ADS-B link layer (UAT or 1090ES) and/or adopt
PowerFLARM (for Flarm-Flarm). This is one reason I also claim that ADS-
B alone in gliders is not practical in the USA until somebody develops
a low cost dual-link layer receiver that can receive directly on both
1090ES and UAT. The ADS-R overage is a reason that busy ridge soaring
locations might want to be looking at the ADS-B GBT (ground station)
coverage maps and getting a feel how much this will be issue in their
area. Something probably a good idea for the SSA to be pushing to have
happen/coordinate.

Sorry to ramble on but this level of detail is really unfortunately
necessary in discussing these technologies.

Darryl

I'm glad you posted this very informative item. As you point out, this
is an incredible mess. It didn't need to be that way, but that's what
you get with government engineering by political committee.

It's too bad that the FLARM guys didn't go after the US market when they
1st started their project in Europe years ago. It might have taken off
in the US GA market and created a defacto standard. No we have a huge
mess with no good answers in sight.

Certainly not a story that gets people excited about spending $$$$s to
upgrade their avionics.

--
Mike Schumann