On Oct 17, 1:43*am, Mark Dickson wrote:
Sorry, but thermalling gliders will almost always show on radar. *

At 23:39 16 October 2010, John Smith wrote:

Mark Dickson wrote:
No, it's Ryanair. *They always look for direct routings, even if it
takes them outside controlled airspace.

They can ask as much as they want, it's the controller authority to
allow it or not. But how can I explain this to somebody who
doesn't even
know that class E airspace is controlled?

Contrary to popular myth, gliders show
as a primary return on radar displays

Contrary to popular myth, stationary primary targets are filtered
out by
the radar software, hence thermalling gliders don't show on the
controller's display.



John is right, and we need to be careful with claims like this because
misunderstanding around statements like this can lead people to
dismiss the role of transponders in providing a valuable tool for
traffic awareness/separation, especially near those airliners and fast
jets.

The answer is both yes (from a technically possible viewpoint) but in
practice it is almost certainly no.

A modern primary radar system will usually have no problem detecting a
glider under benign circumstances, including a fiberglass glider (not
carbon) -- there is enough metal in the glider to show up. However in
practice to have the radar set to detect the glider the controllers
will be seeing all kinds of ground and other clutter (birds, traffic
on roads/freeways, wind turbines, ....). In practice in most places
the Doppler discriminators aka "MTI" (Motion Target Indicator) will be
set to reduce all this clutter and give the radar operator a usable
display. In that practical situation they won't see slow speed gliders
thermalling, those targets would have be removed by the MTI.

It is not possible to say more without knowing the particular
situation. The clutter and other issues, type of radar and target
ranges and elevation etc. If it important you can followup with your
local ATC radar facility and ask them. But I expect the answer in
practice is they will not be able to usefully observe a glider from a
primary radar return.

And even if they could observe the glider the radar likely only
provides location, with no elevation data. e.g. for all civil approach/
terminal radar in the USA. And even if a radar system (like the ARSR-4
used in the USA for civil en-route and CONUS surveillance) does
provide some crude primary radar elevation data it is not always clear
this is passed to particular ATC operators at all, and if it is it is
unlikely to be useful for usual ATC separation services.


Darryl