On 2/29/12 9:41 PM, Mike Schumann wrote:
On Feb 29, 5:02 pm, Darryl wrote:
On 2/29/12 8:56 AM, Peter von Tresckow wrote:

I was going to meet up with a soaring buddy who has a Power Flarm, and take
it flying in my flying club's DA40 to see what traffic it will display. Our
DA40 has a G1000 with the old mode S traffic display, so we can compare the
results.

My question is related to what the ADS-B in capabilities of the power flarm
are. Does it just receive the 1080ES signals from ADS-B equipped planes, or
does it also pick up on the ground station based traffic info?

Thanks

Peter

Actually it's a good question...and a very good thing to want to do some
tests/experiment with. Its the type of question that I hope any ADS-B
data-in/receiver early adopter would ask. I'll try to give you a
detailed enough answer to be useful, but let me know if this is not
clear or needs more explanation. This is very USA specific. Things are
simpler, at least in concept, in Europe and other locations that only
support ADS-B over 1090ES and don't use the USA approach with both
1090ES and UAT link layers. European ATC organizations also do not
provide TIS-B like services over 1090ES.

In the USA ground based ADS-B traffic services are ADS-R and TIS-B.
ADS-R is the relay of traffic broadcasts between UAT and 1090ES link
layers and vice versa. TIS-B is the transmission of SSR radar derived
traffic information over ADS-B and is analogous to the Mode S TIS
service the DA40's G1000's GTX-33 transponder will receive today (but
TIS-B is completely separate to/different in implementation to Mode-S TIS).

The ground based ADS-B ADS-R and TIS-B services are only broadcast to
your if your aircraft is equipped with ADS-B data-out, and that data-out
equipment needs to be properly configured to describe to that ground
infrastructure in this case that you aircraft had a 1090 ES receiver.
The ground based system then transmits ADS-R and TIS-B traffic data for
aircraft withing for a cylinder shaped volume surrounding your aircraft.
Since it is unlikely your DA-40 has 1090ES (or UAT) data-out the ground
based infrastructure simply won't transit those services for you. To
receive these services you also need to be within range of an ADS-B
ground station (aka Ground Based Transceiver -- GBT) and those ADS-R and
TIS-B services need to be deployed for the area you are flying in.
(TIS-B especially requires complex integration with SSR radar
systems--and you need to be clear if that TIS-B integration is for
approach and/or area/enroute radar coverage). In general good luck
trying to find out what exactly is deployed where and when and what the
actual low-altitude coverage you should expect where you fly -- but the
receiver should announce if you have or are leaving service coverage
(again only if you have a properly configured ADS-B data-out equipment).
There are some popular gliding areas like around the great
Basin/Parowan/Inyokern Valley where at least past FAA predictions of
ADS-B ground station coverage were pretty horrible, in other areas it
can be as good as down to hundreds of feet AGL or lower.

Be careful doing quick tests and convincing yourself that any ADS-B
system is receiving ADS-R or TIS-B data. Your receiver may be seeing
broadcasts from the ground infrastructure for other aircraft (that are
equipped with ADS-B data-out and data-in capabilities). You really care
about traffic conflicts/threats to your aircraft, not threats to some
random third party aircraft, -- and that TIS-B and ADS-R traffic data
being broadcast for other aircraft may disappear off your traffic
display as that traffic flies away from that other aircraft...

The usefulness of the 1090ES ADS-B receiver in the PowerFLARM will be
receiving 1090ES ADS-B direct signals from other aircraft as they equip.
with 1090ES data-out. High performance aircraft , especially airliners,
(because of 1990ES requirements for flight in Class A airspace and
European airspace flights) and many GA aircraft (because of the ease of
piggybacking the 1090ES electronics, certification and
sales/marketing/distribution costs onto existing popular GA transponder
products e.g, the Garmin GTX-330 ES/GTX-33 ES) and gliders (because of
the popularity of the 1090ES data-out capable Trig TT21/22
transponders). Currently the FAA is requiring STC approvals for ADS-B
data-out installs in all certified aircraft. That appears to have
effectively stalled ADS-B data-out adoption in GA aircraft in the USA,
although avionics vendors and their partners are working on STCs for
some popular aircraft types (no don't hold your breath for any glider
STCs).

But it gets worse,... even assuming your DA-40 is eventfully upgraded to
ADS-B data-out with a GTX-33ES transponder (with the ADS-B data-out GPS
data typically provided by the GIA-63W already in the G1000 panel). Now
that aircraft has ADS-B data-out but no data-in (unless you also add a
Garmin 800 series traffic system). So the GTX33ES will not be configured
to transmit the capability code bits that tell the ground infrastructure
the aircraft has a 1090ES (or UAT) data-in capability. So you as a pilot
or owner/pilot approaches the aircraft with a PowerFLARM or any other
portable ADS-B receiver in you hand, what do you do? Can you practically
and legally change the ADS-B data-out capability code setup of the
GTX-33ES transponder? Do the transponder configuration menus even let
you do this? BTW when many avionics vendors (including Garmin) are asked
this question they get very shy...

Again the use of PowerFLARM totady is for glider-glider or
glider-towplane use where with both aircraft having a PowerFLARM it all
"just works". The practical use of the 1090ES data-in capability of
PowerFLARM today is directly receiving 1090ES transmissions from those
aircraft equipped with 1090ES data-out. That's potentially interesting
today where we have say 1090ES equipped airliners flying near GA or
glider traffic. And for glider pilots who do own a PowerFLARM and have
buddies with experimental gliders (and therefore immune to ADS-B
data-out STC requirements) and Trig TT21/22 transponders--it is
potentially interesting to encourge those owners to enable ADS-B
data-out on their Trig transponders so you can potentially "see" them at
much longer distances than possible using PowerFLARM-PowerFLARM. It also
may be interesting to track those 1090ES equipped gliders from a 1090ES
ground station. (yes APRS folks, I know amateur radio based APRS
tracking is already well proven in practical use doing that today).

There are web sites that use volunteer ground station receivers that
track ADS-B equipped flights (in practice they those systems are all
1090ES based) traffic -- e.g. seehttp://www.radarvirtuel.comIf you
happen to live in an area that has ground receiver coverage from one of
these services it might give you an idea of the 1090ES data-out equipped
traffic near where you fly (its not much today... that current STC
requirement is a likely factor here, that adoption should change
significantly as we get closer to year 2020 mandatory ADS-B data out
carriage requirements for power aircraft, similar to transponder
requirements today). And I simply expect many of the more modern
transponder equipped GA aircraft to upgrade their transponders to add
1090ES data out capability.

Note I have not addressed whether the PowerFLARM will actually
receive/display ADS-R or TIS-B messages even if your aircraft is
properly set up with ADS-B data-out. I just don't know for sure if ADS-R
or TIS-B capability is supported today in the PowerFLARM--and for the
reasons described above its likely not even important to know. And you
likely want to display TIS-B traffic using different symbols and
implying the position is much less accurately known than ADS-B direct or
Flarm traffic. Attempting to Deduplicate TIS-B and Mode-C PCAS threats
is also a challenging area for PoweFLARM to implement well (but
relatively easy with Mode-S threats since both signals include a unique
ICAO ID). But overall given how messy ADS-B TIS-B is I am really happy
that the Flarm guys decided to implement Mode C and S PCAS in PoweFLARM
(an obvious choice in many ways since here is no TIS-B in Europe).

Darryl

How about someone from the FLARM team answering the simple question:
Does PowerFlarm display TIS-B traffic received from a ADS-B ground
station, assuming that the aircraft is properly transmitting a
properly configured ADS-B out signal. The second logical question is
whether PowerFlarm can function as a GPS source for the Trig 21/22
transponder so that ADS-B out can be configured in those gliders that
have both pieces of equipment.


The answer to the second question really depends on the question, is it
for the PowerFLARM to just "work" as a GPS source for ADS-B data-out or
to meet the FAA performance/certification requirements for the FAA 2020
carriage mandate? Since the PowerFLARM does not contain a TSO-C166b or
TSO-C154c GPS source it will never be usable to meet the FAA carriage
mandate requirements and also therefore unlikely to ever be approved as
part of the currently required installation STC for ADS-B data-out--and
therefore just not allowed today in any certified aircraft. But to the
extent the PowerFLARM can be set to just send plain NEMA data on its
serial connection and the Trig TT21/22 can be configured to receive GPS
data for ADS-B data-out over serial NEMA I expect this to work (in a
non-FAA approved way) today, with care needed in thinking abut if that
NEMA data-out serial connection from the PowerFLARM is also required to
provide extra things like GPS or Flarm traffic data traffic to PDA or
other navigation or traffic displays (just about all configurations
should be doable with a K6 NEMA Mux).

BTW no NEMA based GPS connection is every going to meet the current TSO
approval requirements since the extra capabilities of the aviation data
format used in TSO approved GPS sources is an important part of this
picture. The real hope here would be for the FAA to waive the ADS-B GPS
source TSO requirements for certain VFR traffic (including gliders).

The current Trig TT also does not meet the FAA's 2020 ADS-B data-out
carriage requirements. Specifically the TT21/22 are RTCA DO-260a
compliant devices and the FAA mandate requires DO-260b compliance (and
that is expected to just be a firmware update for the Trig TT-21/22
transponders, something that may well be in test/shipping already for
all I know. Other vendor's currently shipping ADS-B data out devices,
including 1090ES and UAT devices also do not met the latest aka "b-rev"
RTCA compliance required in the 2020 carriage mandate. The difference
between a and b-rev affects the interpretation/meaning of the capability
code bits and is potentially important to a discussion on TIS-B service,
but it is all so frigging complex, who know for sure....

Darryl

Mike Schumann