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Risk Assessment Basics
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North American Fatal
Accident Risk
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The following risk assessment shows that in the next 10 years there is
about a 25% probability that a large jet transport will be involved in a
fatal bird strike related accident in the U.S.
or Canada.
Background
Bird strikes to aircraft have been a concern since the first recorded fatal
bird strike in 1912. More recently, bird strikes have led to fatal accidents
for large military aircraft in both 1995 and 1996 and to a commercial
airliner in 1988. Increasing North American populations of birds such as
geese and ducks have led to a significant increase in the threat to aircraft,
especially in areas on or near airports. The probability of a fatal bird
strike accident can be estimated based on the past bird strike record.
Specifically, the following analysis will estimate the probability of a fatal
accident involving a bird strike to a large jet transport aircraft occurring
in the next ten years in the U.S.
or Canada.
Risk Assessment Basics
Risk is defined as the combination of a specific hazard and the likelihood of
that hazard. The specific hazards in this context are bird strike events that
result in:
- Both fatalities and
aircraft hull loss,
- Aircraft hull loss
only, or
- Other economic losses
($26 million wildlife losses 1993-1995 from FAA reports).
 The likelihood of these three hazards can be roughly estimated from
the following information:
- Fatal and non-fatal
worldwide hull losses since 1959 (five total, one fatal),
- Total jet transport
flights since 1959 (about 300 million),
- Estimated U.S.
and Canadian large commercial jet transport flights 1999-2008, (80
million),
- Average load factor of
54% (60% for airliners, 0% for cargo jet transports, 10% cargo flights),
- Average passenger
capacity (130),
- Probability a
passenger dies in a fatal bird strike accident (0.5), and
- Cost of average jet
transport (30 million 1997 dollars).
Assuming that the historical world hull loss rate is
roughly current underlying rate in the U.S. and Canada,
P(Hull Loss From a Bird Strike Event) = 5/300M = 1.67 x 10-8
P(Fatal | Hull Loss) = 0.2
P(Fatal Hull Loss Event) = 3.3 x 10-9
P(Fatal Hull Loss Event in U.S. or Canada) = (3.3 x 10-9)(8 x 10+6) =
0.027/yr
Assuming a binomial distribution of events, this would imply that over the
next decade,
P(Zero Fatal Hull Losses) = 0.763
P(One Fatal Hull Loss) = 0.209
P(Two Fatal Hull Losses) = 0.026
P(Three Fatal Hull Losses) = 0.001
Estimated Fatal Hull Losses = 0.209 + 2(0.026) + 3(0.001) = 0.263
Note: This last figure means that in the next 10 years there is about
a 25% chance of a fatal bird strike accident involving a large jet transport
in the U.S. or Canada
Estimated Fatalities = 9.2 = (0.263)(130)(0.54)(0.5)
Estimated Non-Fatal Hull Losses = 1.05 = 4(0.263)
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Table 1: Cost In Lives and Property Due to Bird Strikes 1999-2008
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Hazard
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Estimate
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Cost
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Lives Lost
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9.2
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$23 million*
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Aircraft
Losses
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1.3
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$39 million
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Other Losses
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-
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$87 million**
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Total
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$149 million
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* Assume $2.5 million in liability claims per life lost
** Based on 1993-1995 FAA figures for wildlife losses, may represent only 1/20th
of total economic losses
(Cost data from the FAA's Wildlife Strikes to Civil Aircraft in the United
States: 1991-1997)
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