The next step is to determine the impact frequency from intentional overflight of
helicopters. First, determine the number of operations. Earlier in the problem this was
defined as 365/y (or 1/day). Next, get the effective area from Table B-34. The
helicopter crash frequency is shown in Table B-43.
TABLE B-43. Helicopter Crash Frequency.
The next set of steps calculates the total impact frequency (see Section 5.3.3 of the
standard). The analyst begins by adding the near-airport and in-flight results for each
category/subcategory. The results are shown in Table B-44.
TABLE B-44. Total impact frequencies by category/subcategory.
Impact Frequency (per year)
Commercial Aviation Air Carrier
Commercial Aviation Air Taxi
Military Aviation Large Aircraft
Military Aviation Small Aircraft
Total (all aircraft)
Next, the analyst sums up the category/subcategory totals to find the total frequency of
aircraft impact into the facility. This equals 8.4E-6, so the facility does not pass the
impact frequency evaluation guideline in Section 4.2. Therefore, the analyst must
decide which categories to forward to the structural analyst.