Date: 08 Aug 97 05:41:21
From: UnitedSJC@aol.com
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On CNN today (in the daylight) you could see the VOR just meters from the
crash site. Reports said that the aircraft was supposed to be 1800' above
the VOR on the approach. I assume that this VOR was used as part of the
localizer approach. Does anyone have approach plates for GUM to see what the
localizer approach looks like and what role the VOR plays....just curious.
Obviously for KE801, something went wrong w/ the approach.
A couple of theories that I have heard are:
* wind shear (wx was reported as less than favorable)
* inaccurate altimeter setting (causing the aircraft to be lower than
indicated in the cockpit
but I really don't think that the glide slope being inoperative had anything
to do with it. Any comments on this? It will be interesting to see what the
NTSB has to say.
JF Mezei wrote...
>Could someone put this missing glide slope in perspective ?
The glide slope provides vertical guidance to the runway. Approximately 3o
(although this varies from airport to airport). In combination with the
localizer they form an ILS approach (Instrument Landing System). The
localizer provides horizontal guidance.
Absence of a glide slope reverts the approach to a "localizer approach" - the
only difference from an ILS approach being the lack of a smooth descent. In
a localizer approach, radio navigation aids (fixes) are used to determine
distance from the runway, and the published approach plates for the approach
determine the altitude you can descend to after passing each fix.
So, for instance, SFO ILS Rwy 19L has a provision for the glideslope being
inoperative. A profile view of what this should look like is published on
the chart. It begins at 5000' at BERKS at which a descent to 2900' is
permitted. After passing the next fix "SHAKE", a descent to 1900' is
permitted. After passing the next fix "OSTOR" a descent to 340' is
permitted. At the Middle Marker, the airport must be in sight or a missed
approach must be begun.
Following these altitude restrictions ensures terrain clearance.
I know this is a bit wordy and might be hard to understand especially for
someone not familiar with instrument flying. Can anyone else explain it more
clearly?
Also, I don't fly 747's, so I can't explain what shooting a localizer
approach in one is like.
Russ
