Steve Hopkins wrote:
Your point regarding 'Accidents of Omission' is interesting.
If your local drug company marketed an antibiotic that
then proceeded to kill 23 patients, I'm not sure whether
the subsequent litigants would be much impressed by
the uncertain number of lives saved. Yes we need spin
training, and preferably on an annual basis so we don't
forget what to do if, what we spent the previous year
avoiding, accidentally happens. Surely the point at
issue is whether the Puch is a safe vehicle for these
manoeuvres. And if it isn't, then should it be airborne
at all. Certainly the number of accidents involving
the Puch as against the number produced does seem to
indicate that something is amiss. Is there a statistician
out there who could look at the numbers and make a
scientific pronouncement on this? I seem to remember
in my school days, (when Queen Victoria ruled), there
was something called the Chi-squared test which allowed
one to state whether two separate groups of occurrence
were significantly different. Could we compare, for
example, the number of K-13's et al spun in relation
to the numbers built, as against the Puch in the same
manner and pronounce with a specified degree of confidence
whether the accident rate, (spin in's), was significantly
Different?
Would it tell you anything? The point about statistical tests is that you
first eliminate any factors which would skew the result. So you would have
to take into account at least the following:
1. the numbers of spin exercises carried out in puch's against the number in
other types of glider (single and two pew),
2. the training history of the pilots involved in accident free spins
against those in spins where an accident occurred,
3. the flying history of the pilots involved in accident free spins against
those in spins where an accident occurred,
4. the height at which the spin was entered
5. the circumstances of the spin (e.g. deliberate as opposed to induced
6. the method of inducement if that was the method of entry
7. the repair history of the glider (just in case this changed the mass
distribution of same)
8. the weights of the pilots concerned (the mass distribution again)
I'm personally convinced that the issue here is not whether the aircraft is
safe, but whether the pilot is safe to carry out the spinning exercises
concerned - I would only feel safe carrying these exercises with an
instructor whom I knew for certain was current and experienced with carrying
these exercises whichever glider type it is that is used. It is clear that
the puch and other gliders like it can enter a full spin which requires that
the correct procedure be used to recover from it - surely this is a training
issue? And surely it requires that pilots only be allowed to fly gliders
which they have proven their ability to handle?
Rgds,
Derrick.