On 10/29/2010 11:37 AM, kirk.stant wrote:
Mike, I think you do not understand the fundamental difference between
ADS-B and FLARM.

ADS-B is designed for aircraft that do not want to fly close to each
other, and want/need long range situational awareness. Thats probably
where the whole ground station setup comes from - with all it's
disadvantages (coverage, latency, accuracy, etc.) It's a great system
for IFR traffic, and for GA flyers out sightseeing, but it sucks for
gliders in a gaggle or running a ridge.

FLARM, on the other hand, is specifically designed for aircraft
(gliders, helicopters) that often want to fly close to each other,
safely. In a gaggle, running a ridge, heading for the really nice Cu
near the glider field, on the Whites - gliders inherently will
congregate to find the best lift. That is the threat environment
FLARM is designed to cope with. And it's a proven item.

In a perfect world, there would be a SuperFLARM that would add some
sort of ADS-B in/out capability, so the benefits of both would be
present. But until then, FLARM addresses the immediate concern of
many, if not most glider pilots the best. A PowerFLARM, combined with
a mode s transponder, gives a glider most of the useful threat warning
capability of a full up ADS-B setup, and all the advantages of FLARM -
if FLARM is widely adopted by the US soaring community.

But if no-one gets ADS-b in their gliders (show of hands out there?),
then it's of no use in preventing the biggest historical threat -
glider on glider collisions.

I'm planning on getting a PowerFLARM next season to replace my PCAS.
I hope you will to, while waiting for your ADS-B to be installed.


Kirk
66

I think that you have a fundamental misunderstanding of ADS-B. ADS-B is
a general purpose system that is designed to permit aircraft to announce
their position and velocity vectors to anyone who is interested. For
all practical purposes, it has the same accuracy, latency, etc. of FLARM
based systems. It doesn't make any difference if aircraft are flying in
close proximity or not.

FLARM does the same thing and then adds another layer of collision
detection logic on top of that, which is specifically optimized for the
glider world. There is no reason that the same logic could not also be
added on-top of an ADS-B based position sensing technology. In fact,
PowerFLARM claims to be doing this using their 1090ES IN capability, if
the user has ADS-B Out installed.

The ground station ADS-B infrastructure is being deployed for 4 reasons:

1. To provide translation of ADS-B transmissions between UAT and 1090ES
(an unfortunate necessity due to the FAA's decision to go with 2 ADS-B
formats in the US)

2. To transmit TIS-B data. This lets ADS-B IN equipped aircraft see
the position and altitude of Mode C and S Transponder equipped aircraft
which are not yet outfitted with ADS-B transmitters.

3. To transmit additional weather and NOTAM information.

4. To detect ADS-B equipped aircraft so that they can be displayed on
ATC radar displays.


--
Mike Schumann