Re: First 757 crash (and first AA fatality since 1979)

From:         Gunnar Aaboe <gunnaraa@sn.no>
Organization: Oslonett Public Access
Date:         29 Dec 95 22:22:21 
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Followups:    1
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>Does any one have any
>idea about what happened ?  The news here said that the pilot pulled up
>when he saw the mountain.  How could the aircraft get so far off course?
>I wonder if pilot fatigue was a factor... Maybe the pilots woke up when
>the Ground Proximity Warning System warning horn sounded.  I also wonder
>if there was a problem with the ILS system at the airport.
>The pilots may have been attempting to intercept the localizer, but maybe
>the localizer was not in operation. Hopefully we'll learn something
>soon...

There has been a lot of air accident around the world where the pilots
have not reported any problems. I have not seen any statistics but it is
during landing and in bad weather the problems is greatest. (Some one
knows where this statistics can be found?) It was reported that weather
conditons were good in this last accident, but the pictures from the
accident showed frezing rain, and fog drifting.  It was also said by the
reporters that this was a problem for the rescuers.

I have been working with radio transmission systems in nearly 20 years,
and seen how the weather conditions affect the radio waves. The air is
NOT static. It is dynamic and changing the hole time. Radio amaturs (HAM)
use the space between fog and sea (ducht/channel) to get contact over long
distances. On radio link systems they are talking about "space diversity",
using antennas around the main antenna to catch up radiowaves that is
reflected in the fog. I use field strength instruments to messure the
strongest signals to the signal sourch and to get the right direction.
I have seen a lot of times that the signal can bee affected and I have to
do it all over after the weather has changed.  In a learning book I used,
a picture shows warm humid air at the top and cold dry air at the bottom,
and the figure show how the radiowave is reflected.  The French autor
Lucien Boithias writes about all this fenomens in his book Propagation
des ondes radioelectriques dans l'environnement terrestre.  If a pilot
use a ILS where the glidescope is too low he will not see any problems
and not report any.  I don't think this has been the problem in this last
accident, but I think the people who have constructed this ILS systems
and the people using them should know that under spesial conditions they
do have have problem.

--
- Gunnar Aaboe