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

From:         Gunnar Aaboe <>
Organization: Oslonett Public Access
Date:         06 Feb 96 14:15:42 
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  or MIME structure (David T. Medin) wrote:

>Ducting is not a problem on an ILS, if the procedure is correctly
>flown. What can be more serious problem is picking up a false lobe of
>the glideslope (happened to me once during training as an exercise),
>but again flying the procedure will prevent this. The fixes used along
>with altitude vary in their type (VOR, DME, NDB, RNAV, 75MHz marker),
>but are not changed appreciably by ducting over the ranges and
>geometries used.

I understand that the ILS consists of one vertical and one horisontal
beem.  The glidescope is on 330 Mhz and the vertical is at apr.110
Mhz.  Let say that the vertical part is 5 deg. off. The pilot will
still get the correct altitude, and I can't see how he will discover
any problem. (He will see himself right on the cross) Let say he
follows an ILS that is affected in som way, which instument is in
priority ? We have had a lot of accident in Norway in bad weather
(fog, freezing rain, snow) and the pilots have not reported problems.
A pilot from Balkan air was making an approach to Oslo Airport
(Gardermoen) last year and was 3 km off course and 250 ft over the
town Nannestad. There have also been a lot of near accident,
discovered by radar operators. "Luftfartsverket" have a special
plane for tracing and controlling instruments on airports, but they
told me that they had to fly tests i clear weather too be able to
monitor the plane with optical instruments.  (They will not be able
to see the problem.) It seems like they are doing a great job trying
to find the reasons to these tradic accident, but it seems like
they look to much upon each accident and too less on common factors
over time. I should like too see some statistics on this type off
accidents. Is it a common factor that accidents happens in bad
weather conditions and during landings ? Why is "pilot error" nearly
always the reason ? (Is this like the dataoperator unable to find
the mistake and clames it is a virus ?) I've been told there is
some research reports on this fenomen, but they are not public...

- Gunnar Aaboe