Wombat,
That was beautifully put: Even I could understand (most of ) it! Thank you
for that so succinct overview.
Regards,
Gary
----- Original Message -----
From: "Mike Cleaver" <[email protected]>
To: "Discussion of issues relating to Soaring in Australia."
<[email protected]>
Sent: Tuesday, May 12, 2009 8:42 PM
Subject: Re: [Aus-soaring] Airspace - FLARM and MITRE
G'Day All
A note about the purpose and technology comparing FLARM to MITRE and
ADS-B.
FLARM was developed in Europe specifically as an aid to sailplanes flying
in
Alpine areas to avoid collisions at very short range (i.e. the
recreational
parallel to TCAS, using GPS position broadcasts instead of transponders).
MITRE was developed in the US specifically to have a means to allow UAVs
to
operate in "public" airspace with manned aircraft - so-called
"interoperability" - again using GPS position broadcasts over a medium
range
to give an electronic version of see and avoid.
ADS-B is a longer-range technology, also using GPS position broadcasts to
replace ground-based secondary surveillance radar for air traffic control
purposes and therefore transmitting mainly to a network of ground
stations.
Whilst secondary radar (including TCAS) relies on a ground (or aircraft
for
TCAS) signal to trigger an aircraft response, all the GPS systems use an
autonomous aircraft transmission. This means that an aircraft can
participate in the system far more cheaply and efficiently than with
radar.
In spite of this, some of the ADS-B proponents want to link it to the
latest
(most costly, complex and possibly most error-prone) Mode S (for Select)
secondary radar. The UK CAA is among these and has drawn a lot of
criticism
from particularly the gliding and hang gliding community. There is no
reason
why ADS-B and radar should be linked like this, other than the fact they
use
the same frequency of 1090 MHz. All these systems use wavelengths around 3
cm to penetrate haze and cloud.
There is also no reason why ADS-B cannot also be used to show other
aircraft
where a user is, and so ADS-B IN has been developed to display the
position
of other aircraft using the technology - this is very similar to the MITRE
concept, and to a lesser degree of precision, FLARM - which is designed to
enhance see-and-avoid as well as assist separation. All of them can also,
to
a limited degree, allow one user to track another user (the primary job of
ADS-B and radar).
The frequencies DO vary - ADS-B uses 1090 MHz worldwide whilst MITRE uses
978 MHz in the US, and FLARM uses 921 MHz in Australia 869.25 MHz in New
Zealand, and 868 point something MHz in Europe. It looks as if there is
some
regulatory acceptance of FLARM for other than gliders - for instance
rescue
helicopters in Switzerland use it as well.
So all the hoo-ha in the US is because NTSB - the equivalent to our ATSB -
got it into their heads when investigating a few midair collisions
involving
gliders and particularly the one the year before last with the Biz Jet in
the Rockies that the MITRE concept would have prevented the collision.
Hence
they recommended (quite impractically, since it is not intended for
production at the moment and is nowhere near a mature technology) that all
light aircraft and gliders that cannot support a radar transponder and the
TCAS technology should be fitted with it.
The source Chris quoted, "The Examiner", has latched onto this and is
criticising the FAA for not mandating it, trying to create a "media
stink".
In this case, little more use than asking for automatic variable
speed-limiters on every vehicle on the roads, triggered by radio alerts
from
a GPS based system to apply the appropriate speed limit. It's
theoretically
possible, but not technologically feasible yet even if it was genuinely
desirable and affordable.
Wombat
----- Original Message -----
From: "Urs Rothacher" <[email protected]>
To: "'Discussion of issues relating to Soaring in Australia.'"
<[email protected]>
Sent: Tuesday, May 12, 2009 6:56 AM
Subject: Re: [Aus-soaring] Airspace FYI
The MITRE device is a prototype for UAT ADS-B (Australia uses 1090MHz
ADS-B which is incompatible).
http://en.wikipedia.org/wiki/ADS-B#ADS-B_physical_layer
Furthermore it is transmit only and MITRE has no intention of developing
a
certifiable, usable product.
Urs - FLARM
here's a link:
http://www.mitre.org/news/digest/aviation/06_08/av_uat.html
Mike
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