Ian wrote:
On Fri, 21 Jul 2006 04:47:04 +0000, Mike Schumann wrote:

Would the MTI also filter you out if you had a Mode C transponder?

Yes, it can do, depending on the settings of the filters. We had this
problem with the ATC at Cape Town International in South Africa.

There was a problem with Mode C Transponder equipped gliders flying in
wave, disappearing off the radar screens. The problem was found to be due
to speed filters in place on the equipment. Worse still the controllers
had call a technician if they wanted the filters adjusted. As I understand
the filters were set to filter out aircraft taxing on the ground at low
speed.

The local pilots and the controllers are now aware of the problem and the
radar has since been upgraded so this problem is under control.

But the problem is worth knowing about if you have a transponder in your
glider.

I'm not aware of this being a problem the USA. As I understand it, the
taxiing problem can be dealt with by by using proximity and altitude
filters, not speed filters. I'm told there are places where aircraft
squawking the VFR code (1200) may be filtered out, such as the Los
Angeles airspace, but these (very few) places are not where we are soaring!


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Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
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