ADS-B transceivers do not include any collission avoidance logic. They
purely send and receive aircraft type information along with possition and
velocity vector information.

Traffic information that is received by an ADS-B transeiver, either from
another ADS-B transmitter or from an ADS-B ground station is passed to
whatever display device the user wants to interface to the unit. This can
be another GPS display, an IPAQ running a navigation program like See You
Mobile, or even an iPhone running a custom app to display aircraft possition
data.

There is nothing stopping anyone from developing the same or more
sophisticated traffic warning logic in these attached devices that are
currently available with FLARM. Personally, I believe that an audio alert
that gives you traffic warnings relative to your current heading and
altitude (i.e. "Traffic closing at 100 knots, 1/2 mile 3 o'clock, 100 ft low
and climbing") would be very useful for glider applications. I can imagine
that software vendors would add these functions to their offerings, or
someone could start an open source software effort to develop these types of
applications. Once the raw data is available, and ADS-B units are being
deployed in volume, inovation in this area is bound to be very rapid.

Mike Schumann

"johngalloway" wrote in message
...
I think that it helps to think of Flarm as being the algorithm and
radio transmission protocol and not the hardware. The unique feature
of Flarm is that it broadcasts predictions of a glider's flight path
based on the characteristics of glider flight (i.e including a lot of
turning and circling flight) and compares its own prediction with
those of the other received broadcasts. Given the agreed close
proximity of a lot of glider flying (eg circuits, thermalling, ridge
soaring, cruising on shared task etc) then without a proven and
common glider specific predictive algorithm any hardware technology
would be unusable for inter-glider collision avoidance because of
excessive alerts generated by proximities and paths that would be
unacceptable to general and commercial aviation.

If a transponder or ADSB equipment manufacturer wanted to make his
product useful for glider/glider or glider/low speed power collision
avoidance than he would need to include glider specific predictive
algorithm. He could then either license and use the proprietary and
proven Flarm algorithm or develop another one. The latter course
would have the 3 serious disadvantages of significant extra
development costs, development time delay, and a reduction of
performance as different algorithms in different gliders might result
in one glider pilot receiving a collision alert the other not.

The obvious way forward for transpdonder/ADSB manufacturers is that
which is being developed in Europe i.e. a common display that will
show inputs from Flarm units and transponder/ADSB.

Flarm functionality is already included in numerous other products
(varios and data recorders) and there is no reason why it should not
be included in future US or European transponder or ADSB boxes if the
market were sufficient.

Ergo the whole discussion based on the idea that Flarm and ADSB are
alternatives to one another is based on a misconception that, I have
to say, persists in the minds of many UK as well as US glider pilots.

John Galloway

( co-author of the 2007 Scottish Gliding Union Flarm trial report:
http://www.flarm.com/news/SGU_Flarm_Report.pdf )