Nimbus 4 Accident

I think we have to accept that there are occasions
when the finding of an accident report should be 'I
don't know but........'
In the case of the Nimbus 4 accident(s) there are so
many factors which 'may' have occurred that a definitive
conclusion is almost impossible, the best that anyone
can do is speculate, and this applies to most glider
accidents where there are no living witnesses. It is
very easy to attribute the cause to human factors and
in many cases this may be true but there is always
the possibility that there is an unknown factor. What
I have taken from these reports is that it would appear
that there is a point at which a situation becomes
irrecoverable and this point maybe reached quicker
in big wing gliders thatn in small ones and the response
must be to act to prevent the situation ever arising.
To me this means that care should be taken to never
spin or enter a spiral dive which may mean smaller
bank angles and higher airspeed in turbulent conditions
even if this means that some performance is lost.
There are plenty of examples of problems with aircraft
getting into irrecoverable situations, The DH Chipmunk
was just one such example. Modern aircraft, designed
for performance at the expense of handling such as
the SEPECAT Jaguar are know to be almost irrecoverable
if they depart from flight. In the case of the Jaguar
this was discovered during testing and the pilot had
the option of departing the aircraft, survived and
was able to tell the story. While not wishing to digress
the discussion too much we have a similar situation
involving the Puchaz where there have been several
fatal spin ins. It has been found in most cases that
the pilot must have mishandled the controls and this
may indeed be the case however this has to be speculative.
It is not beyond the realms of possibility that there
are some loading conditions and other circumstances
which make recovery from the spin impossible, we cannot
know for certain as there are no living witnesses to
these events. While this may be thought unlikely the
DH Chipmunk is an example of this and several pilots
died before the true problem was realised and anti
spin strakes were added. Test flying can never duplicate
every loading condition or minor difference in construction
and I believe it is very dangerous to assume, that
in the absence of any other cause, the pilot must have
been at fault.
Perhaps the lesson to be learned from all this is that
we know less that we think we do and 'exploring the
envelope' can bring us closer to disaster. It is a
matter of personal choice as to whether we accept this
risk.
In this context Stans assessment has cogent arguments
but must be speculative, we simply will never know.
Not knowing is propbably the most difficult thing that
we as human beings have to accept.

DAJ ASW17 401
At 00:00 08 July 2005, W.J. \bill\ Dean \u.K.\. wrote:
I have never flown a glider of more than about 20 metres
span (ASW 17,
Jantar 2).

However, I am in the process of asking for other pilots'
experience.

One such pilot's reply includes the following:

From your experience of big Nimbi do you think there
is merit in Stan's
ideas?

'Only to the extent that you fly a big glider like
a big glider, not like
a Spitfire. You adjust all your flying to the fact
that you are flying
a big ship. For instance to adjusting your thermalling
technique to
gradual bank angle changes rather than spirited use
of controls to roll
in and out of thermals.

'I have always said about large span gliders, of whatever
make, that you
regard them like flying a 747 Jumbo. Not like an agile
15m glider.

'For instance, in a very turbulent thermal such as
what you often get
over power stations, I often am reluctant to put on
over about 15
degrees of bank. Yes, fifteen degrees. I do not wish
to be sucked in
to a 'loss of control' situation like Ivans and Engen
or the Levers.

Which particular brand of Nimbus do you fly?

'4DM. I am entirely happy with it but I fly it like
the big glider that
it is.'

I would like to add the following:

On the question of use of air-brakes, it would appear
that they were not
opened in the case of the Spanish accident.

In the case of the Minden accident, there was correspondence
on Rec.
Aviation Soaring when the report was published by others
who had experience
of the inadvertent deployment of the brakes at high
speed in turbulence;
the suggestion was that deployment may have been uncommanded.

In addition, Dick Johnson posted that with the Minden
accident there may
have been a problem with the oxygen system undiscoverable
after the crash,
such as oxygen tanks filled with Nitrogen (not entirely
unknown I am
afraid).

It is also notable that whereas there seems to have
been no attempt to bale
out with the Minden accident, with the Spanish accident
both pilots did bale
out and deploy there parachutes, but unfortunately
one of them had his
canopy foul of the wreckage which brought him down
with it.

W.J. (Bill) Dean (U.K.).
Remove 'ic' to reply.


'Bill' wrote in message
oups.com...

I posted the message below on the thread, 'Nimbus
4DT accident 31 July
2000 in Spain.' I am posting it again for better
visibility.

Stan Hall presented his analysis of the Nimbus-4DB
accident in Minden,
NV, 1999. Stan's analysis is scary, to say the least.

The article, Probing for the Smoking Gun, was reprinted
in the Soaring
Association of Canada's free flight, 2/04. Go to
the link below. Click
on free flight on the side bar. Go to free flight
back issues - 2004 -
issue 2. Down load the PDF file.

http://www.sac.ca/

Bill Feldbaumer 09