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34 25 compared to the actual frequency for the eight airports. Accidents Incidents The second step was to compare the risk levels estimated 20 from the analysis with the actual risk rates for the sample of Number of Events Total 15 airports. 10 Validation of Frequency Models 5 Figure 41 presents incident frequency rates for each type of incident and for three different estimates: the historical 0 LDOR LDUS LDVO TOOR TOVO frequency rate in the United States, the actual incident rate Type of Incident/Accident for the sample of eight airports, and the estimated frequency rate for the sample of airports. The rates for the sample Figure 40. Summary of accidents and incidents at were calculated based on the weighted average for the eight surveyed airports since 1981. airports. The actual rate represents the total number of in- cidents from 1981 to 2009 divided by the total volume of on the average annual volume of operations during the past operations during the same period. The figure shows these 10 years and the average level of risk for the entire airport, results in both graphical and tabular format. Some differ- as shown in column 5 of Table 9. A "critical event" is the ences were expected given the small sample size of eight airports focus of the analysis, and it may be an incident or an acci- surveyed. dent. When running the analysis for risk, a critical event is The results presented in Figure 41 demonstrate excellent considered a single accident or an event in which substan- agreement between the accident rates for the sample of air- tial damage to the aircraft and/or injury to passengers is the ports and the historical rate for all the airports in the United consequence. States. The results concur that the sample of airports is rep- The most critical runway end is identified based on the resentative of conditions for the population of airports in the risk of overruns and undershoots only. This risk is associated United States. The largest difference was found for landing with the operations challenging the RSA adjacent to the run- veer-offs; however, the incident rate, particularly for Fort way end. The runway end is identified based on the approach Lauderdale Executive Airport, was unusually high during the end of the runway. The last two columns of Table 9 contain analysis period. the incident type with the highest chance of occurring and The second conclusion drawn from these results is that the the associated runway. actual frequency rates for the eight airports agreed with the es- The validation effort was divided in two steps. The first timated frequency rates for this sample. It is important to note step was to determine that the eight airports selected were that frequency rates involve both accidents and incidents, with representative of conditions across the United States. Al- no distinction for the level of severity. though this is not an analysis required for validating the The plot in Figure 41 also shows excellent agreement between approach, the comparison helped gain confidence of the actual and estimated frequency values for each type of incident. applicability of the risk assessment to other airports. Also, Therefore, there is no need to recalibrate the frequency models the estimated frequency rates of the airport sample were or to apply adjustment factors. Table 9. Summary of analysis results for airports selected for validation. Average Annual Airport Most Frequent Avrg Avrg # of Years Highest Risk Incident and Associated Volume of Ops No. of Airport State Airport for One Accident Runway Runway *** for Past 10 yrs Runways Risk to Occur End** (in 2009) Incident Type Rwy ANC AK 293K (290K) 3 2.1E-07 16 14 LDVO 14/32 CRW* WV 50K (71K) 2 5.5E-06 17 15 LDOR 15 FSD SD 69K (86K) 2 3.1E-07 38 15 LDOR 15 FXE FL 169K (261K) 2 8.3E-07 13 31 LDOR 31 GEG WA 82K (81K) 2 4.1E-07 33 21 LDVO 03/21 STL MP 209K (226K) 4 1.8E-07 28 24 LDVO 06/24 DVT AZ 153K (376K) 2 3.7E-07 15 07L TOVO 07L/25R MIA FL 380K (384K) 4 1.4E-07 19 30 LDVO 12/30 * Risk estimated for condition before RSA improvements completed in 2007. ** Runway end with highest probability of overruns and undershoots only. *** Incident with highest probability of occurrence.