
 DOESTD301496
each method is needed. Neither this standard nor the modeling and data technical
support documents contain sitespecific information; rather, they provide guidance on
what sitespecific information is necessary and how to develop it.
Aircraft crash frequencies are estimated using a "fourfactor formula" which considers
(1) the number of operations, (2) the probability that an aircraft will crash, (3) given a
crash, the probability that the aircraft crashes into a 1squaremile area where the facility
is located, and (4) the size of the facility. In this standard, the fourfactor formula is
implemented in two different ways, depending on the flight phase:
For nearairport activities, which consist of takeoffs (i=1) and landings (i=3), the
a.
fourfactor formula is implemented through a combination of sitespecific
information and data obtained by the user of the standard, and a set of tables
(whose origins are discussed in Reference 2) provided in Appendix B of this
standard.
For nonairport activities (i=2), DOE sitespecific values, as well as reasonable
b.
estimates applicable throughout the continental United States, for the expected
number of crashes per square mile per year in the vicinity of the sites (i.e., the
value of the product NPf(x,y)) are provided in Appendix B of this standard; the
fourfactor formula is implemented by combining these with the facility effective
areas to assess frequencies.
Mathematically, the fourfactor formula is:
Nijk
F
Pijk
fijk(x,y)
Aij
(51)
i, j,k
where:
F
=
estimated annual aircraft crash impact frequency for the facility of
interest (no./y);
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