On 8/17/2010 11:42 AM, Andy wrote:
On Aug 16, 10:40 pm, Darryl wrote:
Again that was not what Andy was claiming.

I'd actually prefer it if I made the statements as to what I was
claiming.

I have actually claimed nothing about what PowerFLARM will do as
regard alert suppression.

I have, however, expresseed the hope that PowerFLARM will have
intelligent alert suppression of transponder based (PCAS) targets.
And by that I did mean suppression of certain PCAS targets but not
others.

Certainly it is possible for Power FLARM to determine the squawk code
of a received transponder. In areas where gliders are assigned a
specific discrete code then PowerFLARM could be programmed to handle
targets with this code in a different way from target not squawking
that code.

It would also be possible to track a target based on range and
altitude information. When on tow the tug's transponder signal will
indicate a constant range and a constant altitude difference. Any
other transponder target that could be a threat will appear at the max
detection range and then come progressively closer. It seems quite
reasonable to assume that a well designed system would allow
suppression of the tug alert but still alert for the approaching
threat. It would also be possible to remove the tug transponder from
the suppressed target list when tow release is detected by a
significant change in altitude difference or range.

Similary if I am in a gaggle with several gliders that have
transponders it would be possible to suppress alerting on all those
targets while they remain within a certain range but still provide
alerting to the King Air that approaches from max detection range and
is closing rapidly. Again the suppressed transponders could be removed
for the suppression list if they show an increase in range
corresponding to leaving the thermal.

So my hope is that, if a transponder equipped glider joined my thermal
I will be alerted. When I visually acquire the glider and decide it
is the one causing the alert I select mute. I will then no longer be
alerted to that transponder but will be alerted to any other
transponder target that approaches me. I will then chose to to mute
that alert if I wish, and still be alerted to the next on that
approaches.

All this assumes that the unit is smart enough to keep track of
individual targets based on range (signal strength), altitude, and
perhaps also squawk code. I see no reasons why this is not
technically possible but again make no claim that such a feature is
include in PowerFLARM

Andy
My gut feeling is that an algorithm like what you describe would be much
harder to implement than you envision.

In busy areas, where transponders are constantly being interrogated, you
might be able to track an isolated aircraft using just altitude and
range. Once you have multiple targets at similar altitude and ranges in
the same time periods, it would be very difficult to keep track of which
target is which without also knowing the bearing.

In remote ares the problem is much worse, as transponder interrogations
might not be happening with any regular frequency. As a result you may
see targets suddenly pop up and then disappear.

The only real solution is ADS-B or FLARM, which transmit the actual
position every second. The problem we face is getting everyone
(including power aircraft) to standardize on a single format, so
everyone can see everyone else. The FAA has told us that should be
ADS-B in the US (unfortunately they gave us the option for two flavors).
Hopefully we will see the price of this equipment drop in the next
couple of years to the point where everyone starts jumping on board.

--
Mike Schumann