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My apologies, Brent.
Sorry. I didn't mean to offend anyone. My statistics were from more than
20 years ago, before computers. I hyave since checked the 2004 data on one
responder's suggestion, and found GenAv has three times as many fatalities per
aircraft hour flown than airliners. I expe3ct that saying this will also poffend
someone. My apologies beforehand.
Terrence
----- Original Message -----
Sent: Sunday, July 30, 2006 11:25
PM
Subject: [LML] Re: response to Terrence
O'Neill's posting..
Terrence writes:
<<Have you
researched accidetn data (like I did) and found that the airlines report
safety in terms of passesnger miles? Is a 747 with 500 passengers 500
times safer than one with jujst crew? And since that's abviously a lying
statistic, >>
Don't you just
love statistics. Of the "lower" branches of mathematics it is one of the least
understood, and consequently, most abused. For example, it is statistically
accurate to say that everyone in the United States has slightly less than one
testicle. The average is skewed from a whole number by the slightly higher
population of females, and not because of Lance Armstrong.
Likewise,
Terrence's statistical argument may be accurate (which it does not seem to be
for 2004 data) but it is not relevant. His is taking the actuary's perspective
where the insurance company is insuring the entire airframe and the actuary
must compute the death per flight hour coefficient in order to determine the
insurance premium. This is a risk calculation, not a personal safety
calculation. For the calculation to have relevance to you it must be
expressed in terms of your probability of being one of the
fatalities.
As an individual I only care about my personal risk in
evaluating safety. How many hours do I need to fly before death is a near
certainty. If I happen to be the sole occupant or one of 200 passengers it is
irrelevant as I am just as dead, not 1/200 or 200 times as dead, just dead.
So, from the perspective of my safety I must evaluate the probability of an
accident in terms of my exposure over time, that being passenger
miles.
If we were to take Terrence's argument that the metric it
is aircraft flight hours then it would also be argued that, among
commercial aircraft, the larger the aircraft the less safe it is. Given that
any particular accident would expose more passengers to risk the you would be
wise to fly on carriers with as few passengers as possible. I believe
the raw statistics would run counter to this logic.
Safety must be
evaluated in terms of the individual. Consequently the "event" based
evaluation is skewed by the average passenger load of the compared group. If
the average for GA is 2 passengers and the average for commercial is 50
passengers then the relative ratio between the two is 25.
I did look up
the statistics for 2004 as reported by the NTSB for the US. I also found
this site for a more comprehensive analysis:
http://www.ntsb.gov/Aviation/stats.htm
In
2004, GA had a total of 24 million total flight hours and Commercial (10 seats or more) totaled 23 Million
with flight hours (about the same) GA killed 321 people in airplanes and another 241 on the ground
(562 total) and commercial killed 14 passengers and 26 on the ground (40
total) (14 times more for GA). GA had a total of 1,669 accidents and
commercial had 111 (15 times more for GA). It seems that in the US it is
~15 times safer to fly commercial vs. GA based on flight hours and
perhaps 20 to 50 times that if evaluated by passenger miles.
Remember,
with statistics two plus two can be any number you want it to be, depending on
how you define the conditions.
Regards
Brent
Regan
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