

DOESTD301496
Step 3. Given the orthonormal distance of the facility from each flight source, obtain the
generic aircraft crash location probability per square mile, i.e., f(x,y), for takeoff and
landing for each aircraft category/subcategory. This information is included in Appendix B
as Tables B2 through B13. If the orthonormal distance of a facility falls outside the
boundaries of these tables, the corresponding f(x,y) is assumed to be zero (a
noncontributor).
Step 4. Obtain the aircraft takeoff and landing crash rates, P, for each aircraft category
or subcategory. This information is provided in Table B1 of Appendix B.
Step 5. Calculate the effective area, A, for each aircraft category or subcategory. The
calculation of the effective area consists of two components: the aircraft can crash into
the structure either by skidding or by flying directly into it. To calculate the effective area,
assume that the aircraft skids or flies into the structure in the direction that produces the
largest area, i.e., crashing in a direction perpendicular to the largest diagonal of the
building. The formula for calculating the skid and flyin areas of an aircraft crashing into
a facility are provided as Equations B3 through B5 in Section B.4 of Appendix B. The
effective area is a function of the cotangent of the impact angle, wingspan, and skid
distance of the crashing aircraft. Values of these parameters are given in Section B.4 of
Appendix B.
Step 6. Multiply the values for N, P, f(x,y), and A for each combination of flight source,
flight phase, and aircraft category/subcategory. Sum over flight sources and flight phases
to calculate an impact frequency for each aircraft category/subcategory. (Do not sum the
categories yet; this will be included in a later step.)
Impact Frequency from Nonairport Operations. Even though the expected
5.3.2
frequency of aircraft crashes into a facility due to mishaps occurring during the in
flight phase of operation, is expected to be lower than the frequency associated
with airport operations, the expected frequency cannot be shown to be a
noncontributor to the overall frequency for all facilities. Thus, nonairport
operations must be considered in the impact frequency analysis.
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