On 8/9/2010 11:57 AM, Andy wrote:
On Aug 9, 9:45 am, Mike
wrote:

Why not require ADS-B units instead. Then you'd get the advantages of
FLARM, but you'd also see all of the transponder equipped GA aircraft
(assuming that there was a ground station in the area).

Perhaps because glider pilots would be overwhelmed by nuissance alerts
when contest flying? I have already experienced my PCAS becoming
close to useless as more gliders are fitted with transponders. I
don't need another system crying wolf all the time.

FLARM uses intelligent alerting based on glider flight
characteristics. It has been reported that the nuissance alerting
frequency low enough that it is still useful in high glider traffic
densities.


Andy


There are two parts to FLARM; an ADS-B type position reporting
broadcast function, and a built in collision warning system.

ADS-B transceivers typically do not include any collision warning logic.
Instead they are more like modems. They transmit and receive position
data in addition to receiving weather info, etc. This information is
passed on to some form of graphics display device so that the locations
of other aircraft can be shown on a moving map display relative to your
own aircraft.

The display device, in addition to showing the location of other
aircraft, can also be programmed to provide collision warnings.
Obviously, the typical flight trajectories of gliders are different than
most power aircraft. I suspect that most glider specific moving map
vendors will try to match FLARM's logic to minimize false alarms if they
elect to provide a collision warning function in addition to just
displaying the relative locations of other aircraft.

ADS-B is obviously just in its infancy in the US vs FLARM's development
in Europe. The encouraging news is that the potential size of the US
ADS-B market is much larger than the potential FLARM market in Europe
(when you include the GA power market), so there will undoubtedly be
lots of innovation in the display devices that will provide the
collision warning function. In VFR environments, these devices will not
require FAA approvals, so I expect that technical advancements will be
very rapid, once low cost ADS-B transceivers become widely available.

--
Mike Schumann