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OCR for page 35
35 1.4E-06 U.S. Historical 1.2E-06 Incident Rate (inc/ops) Actual for Sample 1.0E-06 Estimated for Sample 8.0E-07 6.0E-07 4.0E-07 2.0E-07 0.0E+00 LDOR LDUS LDVO TOOR TOVO U.S. Historical 9.5E-07 2.4E-07 1.2E-06 2.4E-07 2.6E-07 Actual for Sample 5.8E-07 2.6E-07 1.1E-06 3.7E-07 2.1E-07 Estimated for Sample 1.2E-06 2.9E-07 7.0E-07 3.1E-07 2.6E-07 Type of Incident Figure 41. Actual frequency of incidents for sample of air- ports compared to historical rates. Validation of Risk Model of any type divided by the total number of operations in the pe- riod evaluated is the actual accident rate for the airport. The second part of the validation effort consisted of the com- Comparison of the actual rate for each type of accident at parison of actual risk rates with those estimated for the sam- each airport is not very helpful because the number of events ple of eight airports. The estimated risk is associated with the is relatively low, given the sample size of airports used in the likelihood of an accident, rather than an incident. According validation. Therefore, the analysis consisted of comparing the to NTSB, accident is defined as an occurrence associated with rates for the whole sample of eight airports. The comparison is the operation of an aircraft where as a result of the operation, made for each type of accident and for the total accident rate. any person receives fatal or serious injury or any aircraft re- The first analysis compared the proportion between acci- ceives substantial damage. This is also the definition used in dents and the total number of incidents. This was an impor- this report to characterize an aircraft accident. tant analysis to validate the consequence approach developed Data presented in Table 8 contain the accidents that took in this study. Three types of ratios were calculated for each place at the eight sample airports from 1981 to 2009. The ratio type of accident: the estimated ratio for the sample of eight between the actual number of accidents in that period divided airports, the actual ratio for the sample, and the historical by the volume of landings or takeoffs at the airport provides the ratio in the United States. The results are shown in Figure 42 actual rate for each type of event. The total number of accidents in both graphical and tabular form. 80% U.S. Historical 70% Risk vs Frequency Ratio Actual for Sample 60% Estimated for Sample 50% 40% 30% 20% 10% 0% LDOR LDUS LDVO TOOR TOVO Total U.S. Historical 24.7% 48.5% 18.6% 50.0% 18.0% 25.7% Actual for Sample 27.3% 40.0% 25.0% 71.4% 0.0% 31.9% Estimated for Sample 31.6% 22.4% 25.6% 27.9% 30.1% 28.5% Type of Accident Figure 42. Percentage of accidents to the total number of incidents.

OCR for page 35
36 4.5E-07 U.S Historical 4.0E-07 (accidents/operations) Actual for Sample 3.5E-07 Estimated for Sample Average Risk 3.0E-07 2.5E-07 2.0E-07 1.5E-07 1.0E-07 5.0E-08 0.0E+00 LDOR LDUS LDVO TOOR TOVO Total U.S Historical 2.3E-07 1.2E-07 2.2E-07 1.2E-07 4.7E-08 3.7E-07 Actual for Sample 1.6E-07 1.1E-07 2.6E-07 2.6E-07 0.0E+00 4.0E-07 Estimated for Sample 3.7E-07 6.4E-08 1.8E-07 8.6E-08 7.9E-08 3.9E-07 Type of Accident Figure 43. Percentage of accidents to the total number of incidents. Again, the results are in excellent agreement with the excep- number of accidents for the sample. The last analysis for valida- tion of the ratio for TOVO since none of the airports included tion was the comparison of actual and estimated risk levels for in the sample had this type of incident. This can be attributed to the sample of airports. The results are presented in Figure 43. chance, since the estimate is in good agreement with the his- Again, the results between estimated and actual values are torical level in the United States. The number of accidents is in excellent agreement. The validation study demonstrates very low when using only eight airports, and larger variations the applicability of the approach and the models developed in were expected when comparing the parameters based on the this study.