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pchapman(at)ionsys.com
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 Posted: Mon Jul 17, 2006 11:17 am Post subject: Accident rate comparisons - was Airplane insurance. |
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The discussion here has been about the relative risks of general
aviation vs. driving. Out of curiosity I once looked at another
comparison of fatality rates, that of flying homebuilts vs. skydiving.
What follows is something I wrote to the EAA. The numbers are a bit
old because it was written in 1997. The EAA didn't publish it, so I
tried again with the smaller Canadian equivalent (RAA), but I heard
nothing from them either. While statistics are a tricky thing to
interpret, you can judge whether they didn't believe the
interpretation of the data, or didn't like the message!
=========== One version of the letter was this:
Homebuilt Aircraft & Relative Risk
In the June issue of "Sport Aviation", Tom Poberezny reported improvements
in US homebuilt aircraft safety statistics over recent years. Despite a
registered fleet that grew about 25% from 1992 to 1996, the number of
accidents remained essentially constant, while fatal accidents and
fatalities dropped roughly 10 to 15%. In 1996, fatal accidents to homebuilts
in the USA numbered 56, out of a registered fleet of 18700.
What wasn't noted in the article is the obvious conclusion that one in every
334 homebuilts is involved in a fatal accident each year. Which is not that
far from saying that if you are the pilot of a homebuilt aircraft, there is
a 1 in 334 chance of getting killed in it each year. Not quite so
good sounding?
Naturally this ignores factors such as distinguishing passenger from pilot
fatalities, higher accident rates during initial test flights only (and
lower thereafter), the number of pilots flying each homebuilt, how an
accident involving two homebuilts is counted, and whether all registered
aircraft are actually flown. Still, the number should be a good ballpark
figure. Using the 1992 figures gives a more pessimistic 1 in 231. As
independent evidence, one report I saw in 1990 on the safety of different
sports and activities (US insurance company data) listed a 1 in 320 fatality
rate for homebuilts per participant, per year.
To gain additional perspective, one can compare the numbers for homebuilts
to an aviation activity that has some reputation for high risk: skydiving.
US and international data on skydiving in recent years indicate a fatality
rate in the neighbourhood of 1 in 1000 participants per year, for
non-students. [Edit: I've done a lot of looking at skydiving statistics and
know the sport well, so I'm confident that the 1 in 1000 was and continues to
be a realistic number.] (Adding in students improves the rate by
something like a
factor of four, as many make only one jump and so are exposed to little "per
participant" risk.)
Conclusion: homebuilts are in some ways three times more
dangerous than skydiving. I didn't expect that when I first started looking
at the numbers.
====================
Peter Chapman
Toronto, Canada
partner in a 601 HDS; 1500 jumps
P.S. - Regarding the discussion on general aviation vs. driving
accident rates mentioned on the King web site: To answer a question,
the site says that the data is for fatalities, not accidents in general.
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frank.hinde(at)hp.com
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