Re: New ground proximity warning.

Date:         27 Dec 96 04:41:06 
From:         faurecm@halcyon.com (C. Marin Faure)
Organization: Northwest Nexus Inc.
References:   1 2 3 4 5
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In article <airliners.1996.2848@ohare.Chicago.COM>, "Peter Mchugh"
<PMCHUGH@mail.hq.faa.gov> wrote:

> dmarble@magnus.acs.ohio-state.edu (Duane F Marble) wrote:
> >A substantial amount of the data used in digital terrain models comes
> >from analog maps (this includes a lot of the data developed for DMA).
> >The digital data can be no better than the original map data.
>
> I understood that Boeing has the DoD digital terrain data base
> (degraded by removing most man made features).  Isn't this is the data
> base which permits low level operation of cruise missile navigation
> systems. and therefore adequate for enroute nav...and improvable at
> terminals for approaches?????

The cruise missiles that zipped between the buildings of Bagdhad were
flying using pre-entered terrain data.  They were not using active
searching to guide them, as any signals emitting from the missiles could
be used to guide ground-to-air-missiles against them (cruise missiles
don't fly very fast and are in fact fairly easy to hit).  The terrain data
used to program a cruise missile is pretty accurate considering that at
times they are following terrain at altitudes of less than 100 feet at
airspeeds in excess of 400 mph to stay below defensive radar coverage.

For terrain data to be useful to an airliner crew, it wouldn't need to be
anywhere near as accurate as the cruise missile data.  All you want to
know is that there is terrain above you in your vicinity, where it is, and
how close you are to it.  In the case of the system I described in my
original post, the system begins emitting warnings when the plane is one
minute from the dangerous terrain, and the standard avoidance procedure is
to climb.

C. Marin Faure
   author, Flying a Floatplane