" wrote in message
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On Feb 12, 5:57 pm, Ed Rasimus wrote:
On Mon, 12 Feb 2007 20:43:54 GMT, "Steven P. McNicoll"



wrote:

"Ed Rasimus" wrote in message
.. .

GCA = Ground Controlled Approach. PAR = Precision Approach Radar (A
GCA with both glide path and centerline guidance. ASR = Air
Surveillance Radar (A GCA with centerline guidance only, using
recommended minimum altitudes at various ranges from touchdown)

Both ASR and PAR are GCA.

A surveillance approach does not necessarily include recommended minimum
altitudes.

Terminology and precision in language again. An ASR has minimum
altitudes and a "begin descent" point after which you can descend to
minimums as fast or as slowly as you choose while being guaranteed
terrain clearance. My insertion of the modifier "recommended" was bad.


Our controller terminology was "X miles from runway" and "descend to
your minimum descent altitude". The controller provided course
trending information and the pilot was expected to maintain separation
from terrain. Recommended altitudes could be provided on final
approach if the pilot requested. The armed services may/may not have
slightly different methods on altitude information.

Well, "the pilot was expected to maintain separation from terrain" only in
the sense that like any other non-precision approach no glidepath info was
provided. If there was a step-down fix on final the aircraft was descended
to that altitude and only instructed to descend to the MDA after passing the
fix.

One other difference between a PAR approach and an ASR approach is
that in the PAR approach the distances as given are from touchdown,
and in the ASR approach distances are from the runway.

Unless it's a "Surveillance approach using PAR azimuth, mileages will be
from touchdown..."

The AN/TPN-8 (-18 with IFF) was an, ummm, interesting piece of gear. It was
pretty much a "one PAR at a time" set-up so the Arrival guy really had to
space them out in the pattern or get the turn to final right on the money to
get the second aircraft within coverage. Yeah, "interesting" that's the
word I was looking for ;-)