From: dick.zeitlin%acc1bbs@ssr.com (Dick Zeitlin) 
Newsgroups: rec.aviation.ifr
Subject: Re: GPS and IFR Approache
Date: 13 Dec 92 00:13:00 GMT
Distribution: world
Organization: Advanced Computer Concepts BBS, New Rochelle, NY 914-654-1981
Reply-To: dick.zeitlin%acc1bbs@ssr.com (Dick Zeitlin) 

YP> .General:
  > .  GPS is the future and it's happening faster than people think.
  > .A couple of the FAA guys even commented that it's happening too fast
  > .for them, very unlike the slowness typically associated with a federal
  > .agency.  Resources are currently being used for designing approaches
  > .and testing them.  There was a 'weak' mention of GPS being formally
  > .adopted within next few years, (I think a number that came around was
  > .2-3 years!!!).  One interesting tidbit is that GPS is expected to
  > .not only be used for IFR approaches but enroute navigation as
  > .well.  If you think about it, with proper software, a GPS receiver
  > .can emulate VORs and NDBs thus eliminating the need for ground
  > .receivers.  ($$$$)  FAA seems to plan that way.

Approval for enroute navigation will almost certainly be before any
approaches are approved.  The TSO for an IFR GPS is "in process" and on
the verge of being released, from what I hear.

The initial approaches will be "overlay" approaches, built on existing
non-precision approaches by replacing the VOR/NDB defined intersections
with geographic definitions for GPS usage.  In a later phase, approaches
may be redesigned to take advantage of the increased accuracy offered by
GPS.

YP> .GPS vs. ILS:
  > .   GPS/DGPS are much easier to install and maintain than ILS, ILS
  > .requires special ground geometry due to the antenna and the cost of
  > .moving soil around to build an ILS in an airport that is does not have
  > .flat land around it, is big.  In addition, maintaining
  > .a clear path for the signal under adverse conditions (i.e. snow) is
  > .rather expensive.  GPS transmitters are easy to maintain and they don't ne
  > .special terrain geometry.  That will allow even the weirdest airports
  > .(from a terrain point of view) to get IFR approaches.  Also, GPS can
  > .be used to provide circled approaches whereas ILS can only provide
  > .straight guidance.

Curved approaches, like MLS can provide, require more compute power and
database info than exist now.  The first TSO'd units will almost
certainly not have that capability.

YP> .GPS and the army:
  > .   The FAA seems to be very happy with the cooperation of the army
  > .regarding guarantees that a minimal level of GPS coverage will be
  > .established.  All designs will be based on that minimum signal capability.

It's actually the Air Force that owns and operates the GPS SVs.  The
issue is that they can and do muck with the system in an unscheduled and
uncontrolled fashion now.  When the full constellation of SVs is up (by
next summer) coverage will not be an issue, but control of the system
and reduction in the number of scheduled and unscheduled tests will be.
The system will not be declared operational by the FAA until these
issues are resolved.

        D/
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 . QMPro 1.0 41-3345 . Bring back A-N airways!!    Dick.Zeitlin%acc1bbs@ssr.com