How dangerous is soaring?

Tom's calculations indicate how hard it is for the human mind to grasp
probability, and thus why we cannot calculate risk properly.

Tom's coin analogy fails because he is looking for an unbroken sequence
of survival, which therefore takes into account the past in predicting
the future. His calculations are cumulative. Even with coin tosses, we
can see that once we ignore the past and stop cumulating results, the
calculation changes.

Thus, at the start of the week, the chance of survival for a week at
coin toss levels is 1 in 128. The chance of surviving for 8 days is
worse, at 1 in 256. However, if our subject survives day 1, his chance
of making day 8 increases to 1 in 128, and by the end of day 7 it has
risen to 50:50. The older he gets, the longer his chances of living
forever! I think (but as a European writing after what UK
government-sponsored has recently described as a "hazardous" level of
wine consumption I cannot be sure) this may be related to Zeno's paradox
(in Tom Stoppard's words, "... thus proving that the arrow never reaches
it's target and Saint Sebastian died of fright").

If we ignore the past, however, each day's chance is the same at 0.5.
Thus Ray (may he live forever) is able to state that next year his
chances will be pretty much the same, if he makes it that far.

Cumulation of probabilities is what the human brain does automatically.
Suppose the chance of being killed on a glider flight is 1 in 1,000. The
mind (without extensive training) deals with this in a number of ways:

1. I can fly safely 999 times, then have to give up or I will certainly
die on the 1,000th. If I'm already dead, I was "statistically" unlucky.

2. I've had 500 flights, so my risk level has risen to 50:50.

3. At my club we fly 1,000 flights a year between us, so one of us is
sure to die flying.

Unless I'm badly mistaken, none of these are true statements.

I try to think as follows:

a. In the UK where I fly, gliding fatalities are on average around 2.5
per annum out of 5,000 pilots, so my "statistical" risk is around 1 in
2,000 of dying through gliding each year.

b. I can do a number of things to reduce my personal risk to less than 1
in 2,000, so I'll try to do those things.

c. This is, to me, an acceptable level of risk for the pleasure I get
from gliding.

The good thing is that these probabilities are not cumulative. I've been
flying for 11 years, so if they were cumulative my "statistical" risk
might be down to under 1 in 20. It ain't.

What can be cumulative are personal mistakes - careless rigging, no
positive check, lack of sleep, etc. etc. These are the things I worry about.


Tom Gardner wrote:
On Nov 1, 2:11 pm, 1LK wrote:
The calculation which yields the 80/1 is only true for the single
instance;

Single instance of what? If it is the "single instance of a day",
then the calculations are correct.

my odds of being here next year are another thing entirely.
For that you need to do mortality computations.

To stay alive for a week, you have to toss "heads" 7 times in a row,
and the probability of that is 0.5 ^ 7 = 0.078125 = 1 in 128
It's not binary, it's multifactorial.

I don't understand: what do you mean by "it" and "multifactorial"?
Binary? Well yes, flipping a coin is binary; that's why I
subsequently
used your figures (that you didn't bother to include).

It might help if you could explain the reasons (based on an
equivalent
example, if you prefer) why you believe that the calculations are
wrong.
Examples I can think of are
- it is not a 1.25% chance of dying on every day, only on some days
- each day shouldn't be treated as independent from the preceding
days (but that doesn't fit with your original statement)

Anyway, I am glad that your mortality isn't as imminent as it
at first appeared.

On Nov 1, 10:46 pm, Chris Reed wrote:
Tom's calculations indicate how hard it is for the human mind to grasp
probability, and thus why we cannot calculate risk properly.

Tom's coin analogy fails because he is looking for an unbroken sequence
of survival,

Well, yes. If I die on Tuesday, it would seem somewhat
optimistic to assume that I'll be alive on Wednesday!
Am I missing something?

which therefore takes into account the past in predicting
the future.

Er, no. Conditional probability and all that!

His calculations are cumulative. Even with coin tosses, we
can see that once we ignore the past and stop cumulating results, the
calculation changes.

Er, for the conditions I stated, no.

Thus, at the start of the week, the chance of survival for a week at
coin toss levels is 1 in 128. The chance of surviving for 8 days is
worse, at 1 in 256. However, if our subject survives day 1, his chance
of making day 8 increases to 1 in 128, and by the end of day 7 it has
risen to 50:50.

True, but missing the point.

The chance of getting to day 7 from day 1 is 1 in 128, so
the chance of getting to day 8 from day 1 is still 1 in 256.
No change.

No one is disputing if you've reached day 7 then the
chance of getting to day 8 is 1 in 2. Conditional probability, etc.

But on day N the chance of getting to day N+356 is
vanishingly small.

The older he gets, the longer his chances of living
forever! I think (but as a European writing after what UK
government-sponsored has recently described as a "hazardous" level of
wine consumption I cannot be sure) this may be related to Zeno's paradox
(in Tom Stoppard's words, "... thus proving that the arrow never reaches
it's target and Saint Sebastian died of fright").

Rats. You took the words right out my mouth! Leibnitz
and Newton also had a few things to say in this area

If we ignore the past, however, each day's chance is the same at 0.5.
Thus Ray (may he live forever) is able to state that next year his
chances will be pretty much the same, if he makes it that far.

Quite correct. But of course we are actually talking about the
chance of him getting there (which would seem to be unfortunately
small based on his statements).

Cumulation of probabilities is what the human brain does automatically.
Suppose the chance of being killed on a glider flight is 1 in 1,000. The
mind (without extensive training) deals with this in a number of ways:

1. I can fly safely 999 times, then have to give up or I will certainly
die on the 1,000th. If I'm already dead, I was "statistically" unlucky.

2. I've had 500 flights, so my risk level has risen to 50:50.

3. At my club we fly 1,000 flights a year between us, so one of us is
sure to die flying.

Unless I'm badly mistaken, none of these are true statements.

Correct (except under pathologically perverse circumstances

I try to think as follows:

a. In the UK where I fly, gliding fatalities are on average around 2.5
per annum out of 5,000 pilots, so my "statistical" risk is around 1 in
2,000 of dying through gliding each year.

b. I can do a number of things to reduce my personal risk to less than 1
in 2,000, so I'll try to do those things.

c. This is, to me, an acceptable level of risk for the pleasure I get
from gliding.

The good thing is that these probabilities are not cumulative. I've been
flying for 11 years, so if they were cumulative my "statistical" risk
might be down to under 1 in 20. It ain't.

I think the concept of "cumulative" is seriously misleading
in this context.

I think what you're really trying to say is that the probability
of dying on day X from cause Y is *not independent* of the
probability of dying on day X+1 from cause Y.

Under such conditions the "1 in P^N" calculation is clearly
and simply invalid.

In the absence of other information, I chose to presume
"independent" and you have chosen "not independent".

On 1 Nov, 22:46, Chris Reed wrote:

If we ignore the past, however, each day's chance is the same at 0.5.
Thus Ray (may he live forever) is able to state that next year his
chances will be pretty much the same, if he makes it that far.

That's not his claim, though. He seems to be saying that his chance of
dying tomorrow is 1 in 80, his chance of dying the day after that is 1
in 80 and so on to 1st November 2008, but that his chance of dying at
all during that year is still only 1 in 80. I do hope he'll explain,
in case I'm missing something obvious ...

Cumulation of probabilities is what the human brain does automatically.
Suppose the chance of being killed on a glider flight is 1 in 1,000. The
mind (without extensive training) deals with this in a number of ways:

The prblem, of course, is that one cannot be killed twice, so it does
not make sense to combine (simply) the probabilities of dying on
different days. Multiple survival is the aim, and survival
probabilities can be combined quite easily. Just recast our statement
as "The chance of surviving a glider flight is 999 in 1,000"...

3. At my club we fly 1,000 flights a year between us, so one of us is
sure to die flying.

There's actually a 63% chance that one of you will have bought the
farm by the end of the year. Get a new safety officer!

a. In the UK where I fly, gliding fatalities are on average around 2.5
per annum out of 5,000 pilots, so my "statistical" risk is around 1 in
2,000 of dying through gliding each year.

Agreed.

b. I can do a number of things to reduce my personal risk to less than 1
in 2,000, so I'll try to do those things.

Agreed.

c. This is, to me, an acceptable level of risk for the pleasure I get
from gliding.

Agreed.

The good thing is that these probabilities are not cumulative. I've been
flying for 11 years, so if they were cumulative my "statistical" risk
might be down to under 1 in 20. It ain't.

Your chance of making it through the next 11 years is still 99.5% I
reckon you can improve that to 99.95% by application of non-stupidity!

Ian

On Nov 1, 7:32 pm, Ian wrote:
On 1 Nov, 22:46, Chris Reed wrote:

If we ignore the past, however, each day's chance is the same at 0.5.
Thus Ray (may he live forever) is able to state that next year his
chances will be pretty much the same, if he makes it that far.

That's not his claim, though. He seems to be saying that his chance of
dying tomorrow is 1 in 80, his chance of dying the day after that is 1
in 80 and so on to 1st November 2008, but that his chance of dying at
all during that year is still only 1 in 80. I do hope he'll explain,
in case I'm missing something obvious ...

Cumulation of probabilities is what the human brain does automatically.
Suppose the chance of being killed on a glider flight is 1 in 1,000. The
mind (without extensive training) deals with this in a number of ways:

The prblem, of course, is that one cannot be killed twice, so it does
not make sense to combine (simply) the probabilities of dying on
different days. Multiple survival is the aim, and survival
probabilities can be combined quite easily. Just recast our statement
as "The chance of surviving a glider flight is 999 in 1,000"...

3. At my club we fly 1,000 flights a year between us, so one of us is
sure to die flying.

There's actually a 63% chance that one of you will have bought the
farm by the end of the year. Get a new safety officer!

a. In the UK where I fly, gliding fatalities are on average around 2.5
per annum out of 5,000 pilots, so my "statistical" risk is around 1 in
2,000 of dying through gliding each year.

Agreed.

b. I can do a number of things to reduce my personal risk to less than 1
in 2,000, so I'll try to do those things.

Agreed.

I appologise for starting a statistical discussion; there's enough of
that at work. The important point is the one made in Chris's post
that gliding carries a risk in the range of one to between two and
three thousand depending on what denominator is used. Serving in Iraq
carries a similar risk, but the population isn't uniform; there's
clearly a difference in being in being part of the rear echelon vs
patrolling the streets. Our population is similarly stratified in
terms of risk.

There are also, unfortunately, factors beyond personal control in
play. As I've aged, I've noted that I need a bit more distance
between myself and the car in front of me. My head needs to swivel to
a greater degree to see things in the periphery. These effects can be
measured/quantified. Medical events such as stroke or MI have been
suggested as the cause of a number of accidents; the ones that killed
the student who soloed ahead of me where I learned to fly in SoCal and
that of a friend who crashed during the return to Kitty Hawk were
likely caused by medical incapacitation. As I age, my risk of such
events increases.

The important thing, IMHO, is to recognize the risk, decide what
you're willing to accept, and, if you choose to go forward, control
what you can and hope that what you can't won't kill you.

Ray Warshaw
1LK


c. This is, to me, an acceptable level of risk for the pleasure I
get
from gliding.

Agreed.

The good thing is that these probabilities are not cumulative. I've been
flying for 11 years, so if they were cumulative my "statistical" risk
might be down to under 1 in 20. It ain't.

Your chance of making it through the next 11 years is still 99.5% I
reckon you can improve that to 99.95% by application of non-stupidity!

Ian

On Nov 2, 12:21 pm, 1LK wrote:
Serving in Iraq
carries a similar risk, but the population isn't uniform; there's
clearly a difference in being in being part of the rear echelon vs
patrolling the streets.

It is always worth comparing one risk with another, as
a sanity check.

During the first Gulf War in 1991, it was safer to be a black GI
on active service in the Gulf than it was to be a black civilian
in Washington DC.

In this case "safer" means probability of non-accidental death
per 100,000 people.

When I first heard that I was sufficiently suspicious that I went
down the library (it was just as the web was arriving) and checked
the sources myself.

The other surprising statistic is the age at which you are
most likely to be a homicide victim in the UK. Most people
presume 16-24, but actually it is three times more
likely to be deliberately killed when you are under 1 year
old. And 55% of those homicides are committed by females.

(N.B. I used "homicide" very deliberately, not murder)

On Oct 31, 7:41 pm, Bob Kuykendall wrote:
...clip...

Observe that the numbers for gliders are 19.45 accidents per 100,000
hours flown, with 5.07 fatal accidents per 100,000 hours. That's
second only to amateur-built aircraft, with 21.6 and 5.5 respectively.

Contrast that with the numbers for single-engine piston-powered
airplanes with 7.91 accidents and 1.41 fatal accidents per 100,000
hours. In 2003 at least, gliders had 245% more accidents and 360% more
fatal accidents per hour than the puddle-jumpers that comprise the
majority of the US general aviation fleet
....clip...

As concerns comparisons between the accident rates of flying and
driving, I defer to this analysis by Harry Mantakos:
http://www.meretrix.com/~harry/flyin...vsdriving.html

Given those numbers, I normally feel fairly confident when I say that
soaring is much more dangerous than driving, and is perhaps comparable
to riding a motorcycle. ...clip...

The fatalities-per-hoiur statistics in soaring were presented at SSA a
couple of years ago, and Judge McWhorter, sitting next to me, compared
it to the fatality rate in coal mining, a famously risky occupation.
Judge quickly calculated in his head that soaring has about a five-
fold greater fatality rate per hour than coal miners.

But he's a mining-safety expert; his next point was not that coal
mining is too dangerous, or that soaring is too dangerous, but that
formal safety practices, taught and followed with discipline, reduce
the fatality experience rate tremendously in coal mining, and would in
soaring also.

The key to devising safety practices is understanding the behavior and
circumstances that increase the incidence of deadly accidents (we call
them 'accidents' because the participants had no intention of having
them).

The key to making safety practices effective is to follow them with
discipline and understanding.

Now, the caveat is that we can ultimately control only our own
behavior; we merely influence others, which is not the same thing. So
we then need to understand also to what extent we are at risk from
others' foolishness or ignorance, or from uncontrollable factors.

In this regard, a colleague stopped riding motorcycle completely,
during college, when he discovered a statistic that said that 2/3 of
motorcycle accidents are due to autos turning left in front of the
motorcycle. Most of the risk was beyond his control, and he wanted to
matriculate through medical school with intact brain and spinal cord.

Another factor is tolerable risk. Several posters have alluded to
this: a single parent with small children will have little tolerance
for personal risk, for the sake of the children. Others have more
room. I'm not here to deride either.

And fear itself is an very aversive emotion. Whether or not the fear
is rational, it's real, and it's distracting. One sensible response
to fear is withdrawal from the situation. If this means to stop
soaring, so be it, for that person. For others, it stimulates
additional study or training, or a change in location or practices.
So be it.

Thanks for listening.

DJ

Gliding is a Risk Sport, as are Motor Racing and Rallying,
Downhill Skiing, Motor Cycling and Mountaineering (all
of which I have tried at some point in my life). The
point is how you manage the risk and how rewarding
you find the activity! Gliding can be as safe or as
dangerous as you want to make it, with low level cross-countries
and mountain flying being riskier than high level local
soaring.

If you fly as your instructor taught you, don't fly
into impossible situations, and above all keep a good
look out for other aircraft, your risks of sudden death
are greatly reduced.

All human activities, driving, crossing the road, etc.,
carry some small degree of risk. Gliding is actually
statistically considerably safer than Horse Riding,
which does not generally seem to be regarded as risky.


Del C

At 01:06 03 November 2007, Danlj wrote:
On Oct 31, 7:41 pm, Bob Kuykendall wrote:
...clip...

Observe that the numbers for gliders are 19.45 accidents
per 100,000
hours flown, with 5.07 fatal accidents per 100,000
hours. That's
second only to amateur-built aircraft, with 21.6 and
5.5 respectively.

Contrast that with the numbers for single-engine piston-powered
airplanes with 7.91 accidents and 1.41 fatal accidents
per 100,000
hours. In 2003 at least, gliders had 245% more accidents
and 360% more
fatal accidents per hour than the puddle-jumpers that
comprise the
majority of the US general aviation fleet
....clip...

As concerns comparisons between the accident rates
of flying and
driving, I defer to this analysis by Harry Mantakos:
http://www.meretrix.com/~harry/flyin...vsdriving.html

Given those numbers, I normally feel fairly confident
when I say that
soaring is much more dangerous than driving, and is
perhaps comparable
to riding a motorcycle. ...clip...

The fatalities-per-hoiur statistics in soaring were
presented at SSA a
couple of years ago, and Judge McWhorter, sitting next
to me, compared
it to the fatality rate in coal mining, a famously
risky occupation.
Judge quickly calculated in his head that soaring has
about a five-
fold greater fatality rate per hour than coal miners.

But he's a mining-safety expert; his next point was
not that coal
mining is too dangerous, or that soaring is too dangerous,
but that
formal safety practices, taught and followed with discipline,
reduce
the fatality experience rate tremendously in coal mining,
and would in
soaring also.

The key to devising safety practices is understanding
the behavior and
circumstances that increase the incidence of deadly
accidents (we call
them 'accidents' because the participants had no intention
of having
them).

The key to making safety practices effective is to
follow them with
discipline and understanding.

Now, the caveat is that we can ultimately control only
our own
behavior; we merely influence others, which is not
the same thing. So
we then need to understand also to what extent we are
at risk from
others' foolishness or ignorance, or from uncontrollable
factors.

In this regard, a colleague stopped riding motorcycle
completely,
during college, when he discovered a statistic that
said that 2/3 of
motorcycle accidents are due to autos turning left
in front of the
motorcycle. Most of the risk was beyond his control,
and he wanted to
matriculate through medical school with intact brain
and spinal cord.

Another factor is tolerable risk. Several posters
have alluded to
this: a single parent with small children will have
little tolerance
for personal risk, for the sake of the children. Others
have more
room. I'm not here to deride either.

And fear itself is an very aversive emotion. Whether
or not the fear
is rational, it's real, and it's distracting. One
sensible response
to fear is withdrawal from the situation. If this
means to stop
soaring, so be it, for that person. For others, it
stimulates
additional study or training, or a change in location
or practices.
So be it.

Thanks for listening.

DJ

On Nov 3, 5:07 am, Del C wrote
Gliding is actually statistically considerably safer than Horse Riding,
which does not generally seem to be regarded as risky.

What are the horse riding statistics and what are they based on based
on? Hours in the saddle or something else? Do horse riders log and
report the hours they ride to some controlling authority that compiles
the statistics? Are the statistics broken down into the many types of
horse riding?

I suspect there is very poor data on the time exposure to most of the
risks that kill people, except of course total hours lived prior to
the fatal event.

Andy

There's statistics, then there's damned statistics,
and then there's liars.

Your chances of having an accident are 1 in 2; either
you will or you won't. Same is true of rope breaks,
of mid-airs, smothering in your sleep, or whatever.
It is up to you each and every time to prevent it.
Be wary!

At 14:12 03 November 2007, Andy wrote:
On Nov 3, 5:07 am, Del C wrote
Gliding is actually statistically considerably safer
than Horse Riding,
which does not generally seem to be regarded as risky.

What are the horse riding statistics and what are they
based on based
on? Hours in the saddle or something else? Do horse
riders log and
report the hours they ride to some controlling authority
that compiles
the statistics? Are the statistics broken down into
the many types of
horse riding?

I suspect there is very poor data on the time exposure
to most of the
risks that kill people, except of course total hours
lived prior to
the fatal event.

Andy

Nyal Williams wrote:
There's statistics, then there's damned statistics,
and then there's liars.

Your chances of having an accident are 1 in 2; either
you will or you won't.

You are confusing "probability" with "possibility". The chances are 3 in
4 of it attracting posts like this one, that discuss probability instead
of safety. I think even Tom Knauff stopped saying that.

Same is true of rope breaks,
of mid-airs, smothering in your sleep, or whatever.
It is up to you each and every time to prevent it.
Be wary!

But your advice is good.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org