On Sep 9, 6:05*am, Ramy wrote:
Average is around 6-7 per year. At this rate we will break 10 before
the year ends!

With such a small expected value the standard deviation is very high
compared to the average.

In a Poisson distribution, the standard deviation is the square root
of the mean, which would be about 2.5 in this case. So, over 20 years
you'd expect to see 1-2 deaths in some year, and 10-11 in some other
year, just from purely random chance. (and, no, it's not
symmetrical .. 15 is a lot more likely than -2)

Assuming that the distribution is binomial or hypergeometric would
give much the same result with more complicated math :-)

(hypergeometric is the best theoretical ft to the situation, as it
allows for the facts both that the population is relatively small and
a given person can die only once. Binomial is a little simpler to work
with and is correct for things that can happen more than once to the
same person. Poisson is even simpler math and is the limit of both
binomial and hypergeometric for a very large population size and small
probability)


1/500 chance per year, makes it 1/20 chance in 25 years! This sounds
about right when you look at how many old time pilots are still
around... This is really sad.

Maybe my club is not typical somehow, but by that measure we should
have had about 5 gliding-related deaths in the 25 years I've been a
member, but there have in fact been zero.

Our club size seems to vary from about 80 members to 120. The *active*
members is I guess around 40, depending on what you call active. There
are ten or so regularly rostered tow pilots and a similar number of
instructors, and there are currently 18 on the "ground controller"
roster.

What accidents have we had? Well, that I can recall:

2010: Cirrus failed to make it back to the airport in heavy sink,
landed on the street breaking glider wing on a pole. Pilot uninjured.

2005: overseas visitor landed club's Std Libelle in a rocky riverbed.
Insurance writeoff. Pilot uninjured.

2005ish: contest outlanding failed to make the selected field (spin?).
Glider repaired. I *think* the pilot suffered a broken leg. Our club
member but flying at a club 500 km away.

1993ish: Blanik following Janus failed to make it back to the field,
landed on the main highway at about 4 pm on Easter Monday. Avoided
cars, wingtip hit a steel pole, severing wingtip and snapping rear
fuselage. Pilot uninjured.


I can't think of any others since I joined the club in 1985.

Our long time chief tow pilot died flying a small twin engined plane
on a commercial passenger service in the Pacific islands. A visiting
summer tow pilot from France later died in a crop duster in Africa.
And we've lost quite a few members to cancer or old age.

I'm sure that any of the four incidents I listed above could have lead
to death. But they didn't, fortunately.

Equally, I'm sure there are dozens of near misses that could have led
to serious damage and injury but didn't.

Every flight is dangerous so I guess the best course is to look at the
actual outcomes, not "gosh that was lucky!"s.