Re: Gliders and Radar

From:         faurecm@halcyon.com (C. Marin Faure)
Organization: Northwest Nexus Inc.
Date:         22 Jul 96 01:53:13 
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In article <airliners.1996.1142@ohare.Chicago.COM>, ability@zetnet.co.uk
(Joe Curry) wrote:

> I have just watched a UK programme that highlights the fact that gliders are
> invisible to radar....
> Surely a glider could be fitted with a radar reflector? Even if the
> glider had radio contact with ATC, they would not be absolutely sure
> of it,s position. What about hang gliders? All that lies between
> safety and disaster is a piece of fabric and a body.

If the glider is metal, it will show up on radar the same as a Cessna or
Piper airplane.  However, the computers in some air traffic control
facilities are set to eliminate all targets that are moving at less than
50 mph.  I don't know if this is still the case, but it was in the
mid-1970s at Approach and Departure Control at Honolulu International.  It
was to keep the highway traffic from showing up on the scopes. I remember
being told and shown by a controller that the Seaflight Boeing jetfoils
that were in operation during that time would suddenly appear on the
screen as they passed through 50 mph.  It was a real pain, the controller
said, because the route the jetfoils took off Waikiki put them under the
flight paths of the jets coming in from the east to land at HNL.  All of a
sudden there would be this target moving right through the flighpaths with
no transponder code or anything.  I suppose with the newer technology
that's in the centers today this wouldn't be as much of a problem, but if
they still drop signals moving less than 50 mph from the scopes, that
could make a glider invisible on radar.  If that's the case, the only
solution would be to install a transponder on the glider.

C. Marin Faure
   author, Flying a Floatplane