
 DOESTD301496
APPENDIX B
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 B34. The
helicopter crash frequency is shown in Table B43.
TABLE B43. Helicopter Crash Frequency.
Average
Number of
Crash
A,
Length of
Frequency
Operations
Rate/Operation
Sq. Miles
Flight (mi)
Helicopter
365
2.5E5
6.6E4
37
3.3E7
The next set of steps calculates the total impact frequency (see Section 5.3.3 of the
standard). The analyst begins by adding the nearairport and inflight results for each
category/subcategory. The results are shown in Table B44.
TABLE B44. Total impact frequencies by category/subcategory.
Category/Subcategory
Impact Frequency (per year)
General Aviation
6.2E6
Commercial Aviation Air Carrier
1.5E7
Commercial Aviation Air Taxi
3.5E7
Military Aviation Large Aircraft
6.4E7
Military Aviation Small Aircraft
6.8E7
Helicopters
3.3E7
Total (all aircraft)
8.4E6
Next, the analyst sums up the category/subcategory totals to find the total frequency of
aircraft impact into the facility. This equals 8.4E6, 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.
B48

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