Glider Safety

On Feb 21, 2:04*pm, Andy wrote:
On Feb 21, 2:04*pm, Tom wrote:

The following is the first of a series of newsletters to be sent to
subscribers to my popular newsletter.
This series of newsletters will review:
Accident causes.
FATALITIES PER THOUSAND
Gliders: Approximately 1 in 2,000
*Autos: *Approximately 1 in 6,000

Tom,

I don't doubt the numbers are horrible but can you please clarify
"FATALITIES PER THOUSAND"? *Per thousand what? *Is this registered
gliders, certificated pilots, hours flown, miles flown...?

thanks

Andy

I have the same question - what is the denominator? In fact there are
two denominators required since you also need to specify a time frame
(typically a year).

If the 1 in 2,000 is per glider pilot per year that would be a lot
worse for glider pilots than per hour or per operation - like takeoff
or landing, or per trip in a car. Most pilots spend a lot less time in
their gliders than in their autos and make a lot more car trips than
glider flights.

If the stats are per pilot then you are three times as likely to have
a fatal accident in your glider for an average person. If it's per
hour then you are 2-3 times as likely to have a fatal auto accident in
any given year.

Based on the number of people I know who have died in each activity
I'm betting Tom's stats are per person per year. I've known maybe a
dozen pilots who have been killed in gliders and can't recall a single
auto accident victim that I had met personally.

It also means that over a 40 year soaring career your probability of
being in a fatal accident is around 1 in 50, or 2% - assuming you fly
the average annual amount of hours over the entire period.

9B

It also means that over a 40 year soaring career your probability of
being in a fatal accident is around 1 in 50, or 2% - assuming you fly
the average annual amount of hours over the entire period.

9B




No, it doesn't. The risk isn't cumulative, it's 1:2,000 each year you fly.

I can guarantee that if you have a fatal accident in year 1, your risk
of repeating it in years 2-40 is 0%.

Bear in mind also that more than 3/4 of fatal accidents seem to have
causes within the pilot's own control so that, if you flew perfectly all
the time, you could reduce that risk to more like 1:8,000.

My philosophy is that 1:2,000 is acceptable, and that I will work to get
it nearer 1:8,000. Still more dangerous than autos per hour, but worth it.

Chris Reed wrote:
It also means that over a 40 year soaring career your probability of
being in a fatal accident is around 1 in 50, or 2% - assuming you fly
the average annual amount of hours over the entire period.

9B


No, it doesn't. The risk isn't cumulative, it's 1:2,000 each year you
fly.
True, but 9B said "over 40 year soaring career".

I can guarantee that if you have a fatal accident in year 1, your risk
of repeating it in years 2-40 is 0%.
True, but irrelevant. I also calculate the risk over a 40 year period as
being 2%, assuming the 1 in 2000 chance/year. YMMV.

Chance of not being in an accident each year = (1 - 0.0005) = 0.9995
For 40 years, chance = 0.9995^40 = 0.98

That's 98% chance of not being in an accident. Lots of assumptions, so
maybe not too instructive.
For 40 years, 1 in 8000 gets it down to 99.5% of not being in an accident.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm http://tinyurl.com/yb3xywl

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

Eric Greenwell wrote:
Chris Reed wrote:
It also means that over a 40 year soaring career your probability of
being in a fatal accident is around 1 in 50, or 2% - assuming you fly
the average annual amount of hours over the entire period.

9B


No, it doesn't. The risk isn't cumulative, it's 1:2,000 each year you
fly.
True, but 9B said "over 40 year soaring career".

I can guarantee that if you have a fatal accident in year 1, your risk
of repeating it in years 2-40 is 0%.
True, but irrelevant. I also calculate the risk over a 40 year period as
being 2%, assuming the 1 in 2000 chance/year. YMMV.

Chance of not being in an accident each year = (1 - 0.0005) = 0.9995
For 40 years, chance = 0.9995^40 = 0.98

That's 98% chance of not being in an accident. Lots of assumptions, so
maybe not too instructive.
For 40 years, 1 in 8000 gets it down to 99.5% of not being in an accident.

OK, I'll accept that as a calculation at the beginning of year 1.

However, I've survived 14 years without a fatal accident so far. In the
remaining 26 of my 40 year career (I hope), that gives me a 0.9995 to
the power 26 chance of a fatal accident (0.987, or a 1.3% chance). If I
make it to the end of year 39 I have a 1:2,000 or 0.0005 chance of a
fatal accident in the final year.

I don't think the probability over a flying career helps understand risk
much on an individual basis, though it's useful for insurers and actuaries.

Much better to think that you have a 1:2,000 chance in the coming year,
and work on getting that ratio to improve in your favour.