From: hopkins@gvlf9-o.gvl.unisys.com (Bill Hopkins)
Newsgroups: rec.aviation
Subject: Re: In-flight radar from ground stations?
Date: 29 Jul 92 20:29:40 GMT
Reply-To: hopkins@gvl.unisys.com
Organization: Paramax Systems Corp (A Unisys Company), Great Valley Labs, PA

In article <1992Jul24.130009.22098@xn.ll.mit.edu> olsen@xn.ll.mit.edu writes:
>
>                          [...] weather data transmission is one of the
>roles envisioned for the Mode-S transponder data link.  Of course,
>I wouldn't hold my breath waiting for Mode-S: it's the radar system
>of the future, and destined to remain so for some time.

Well, it *has* been for quite a while, but that may finally be
changing.  Here's my reading of what's likely to happen.

I expect there will be several Mode S Sensors (the ground stations)
installed in the next year without turning on their Mode S features
(just newer, more accurate and reliable Mode C interrogators), and
that sometime next year the FAA Tech Center folks will be happy
enough with their testing to turn on Mode S.  There are currently
two sensors at the Tech Center for Operational Test & Evaluation,
and one at Lincoln Labs for their enjoyment and entertainment, with
installations at *airports* starting up, um, soon.  (I'd be more
specific, but the plans have changed enough times to make me leery.)

With the sensors in place, there is the opportunity to use the data
link, and not just for ordering the flight crew's lunch.  The data
link is relatively narrowband, and is accessible on the ground side
only through FAA facilities, which makes it tough to pull a Mickey
Rooney "Hey! Let's use the transponders!" kind of deal.  Bandwidth
will probably be the limiting factor for access to the datalink;
the FAA "owns" it and won't give it away lightly.  The design
includes "non-ATC" communication (a Weather Communications Processor
is the only one I've seen cited); I expect WX data in some form
will be a priority.  I also expect (hope?) that Mode S transponders
won't be *required* for GA aircraft for a long time, although they
may become very *useful* in high traffic density areas.

The folks with the sensor at LL (not olsen@xn.ll.mit.edu, he tells
me he's in a different division) have been having a lot of fun with
it, according to reports.  In addition to TIS and datalink stuff
(described in other posts), they've been using it to identify planes
with Mode S transponders that weren't set up right.  The airlines
are busy converting to Mode S transponders, since they gotta.  Each
transponder has putatively unique 24-bit ID, with hex "ffffff"
reserved.  Guess what ID keeps showing up?  Until sensors started
asking for ID's, of course, nobody noticed or cared.

This is all my opinion, of course, since I don't speak for the FAA,
the Paramax/Westinghouse Joint Venture (the sensor developer), or
much of anyone else, for that matter (as my kids keep reminding me).

	Bill (sensors R us) Hopkins

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215-648-2854 or 363-7464        Great Valley Labs, PO Box 517, Paoli, PA 19301
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