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37 a, n = regression coefficients for the x-model; and i = the location parameter for obstacle i. The value of may be estimated based on Kirkland's model for aircraft deceleration over different types of terrain (Kirkland et al., 2004) and crashworthiness speed criteria for aircraft. It should be noted that depends on the type of terrain, type and size of aircraft, and type of obstacle. Frangible objects in the RSA are less prone to causing severe consequences. Lighter aircraft may stop faster and the landing gear configuration also may have an effect on the aircraft deceleration in soft terrain, but these factors are not accounted for in Kirkland's model. D0 is distance to Obstacle, d is distance the aircraft came to stop Area (lightly shaded) between D0 and D0 + represent % occurrences The probability and location models should provide a at low speed (energy) when hitting obstacle (low consequences) quantitative assessment based on operating conditions for a Figure 30. Approach to model consequences specific airplane landing or takeoff at a specific runway. The of overrun/undershoot accidents. consequences model should provide a qualitative assessment of the severity of an accident, based on the location model and the existing runway characteristics, to include dimen- Yf = the critical aircraft location, relative to the obstacle, sions of existing RSA, airplane weight, type, location and size farther from the extended runway axis. of obstacles, and the topography of the surrounding terrain. The same example is depicted in Figure 32 showing the The procedure will allow modeling overrun and under- probability of severe consequences can be represented by the shoot risks for the conditions of the airport being evaluated. lightly shaded area in the probability distribution. The probability of the accident occurring, as well as stopping Combining this approach with the longitudinal distribu- location distances, will be compared to existing geometry of tion approach and the possibility of multiple obstacles, the safety areas and existing obstacles to assess the possible con- risk for accidents with severe consequences can be estimated sequences of the accident, at least qualitatively. using the following model: Psc = N(e m - byci -e - bym fi )e - a( xi + i )n (25) Cost of Accidents i =1 2 As described in the previous chapter, the direct costs of ac- cidents and incidents were estimated for each event having where sufficient information for the computation. This section N = the number of existing obstacles; presents a summary of these costs. RSA y2 x y1 x (dist. to obstacle) y 2000ft 2000ft Figure 31. Modeling consequences.
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38 Lateral Location Probability Psc Obstacle y y1 y2 Figure 32. Modeling likelihood of striking an obstacle. Accident and Incident Average Direct Costs (2007 dollars) 25.00 22.11 Average Cost ($ Million) 20.00 15.43 15.00 10.00 6.72 5.60 4.19 5.00 1.31 0.110.00 0.06 0.00 0.05 0.21 0.00 LDOR ACC LDOR INC LDUS ACC LDUS INC TOOR ACC TOOR INC Aircraft 5.60 0.11 4.19 0.06 6.72 0.05 Injuries 1.31 0.00 22.11 0.00 15.43 0.21 Type of Event Figure 33. Direct cost of accidents and incidents. As mentioned earlier, the intent was to use the data and Table 14. Total and investigation costs find relationships between certain parameters of the accident (2007 dollars, millions). (e.g., wreckage path distance) and the number and level of Type of Event Total Cost Investigation Cost injuries, as well as damage to aircraft. The total consequences LDOR ACC 7.08 0.17 were estimated in terms of total direct costs for injuries, air- LDOR INC 0.11 0.00 craft damage, and accident investigation. LDUS ACC 26.75 0.45 Figure 33 depicts the average cost by type of accident and by LDUS INC 0.06 0.00 severity. Most of the cost for LDORs is attributed to loss of TOOR ACC 22.60 0.46 TOOR INC 0.26 0.00 property or aircraft damage. On the other hand, loss of dollars due to injuries is significantly higher for LDUSs, most likely due to the high speed and energy during these accidents. The average loss of property among the three types of ac- cidents was fairly similar. As expected, the cost of incidents The costs for injuries, aircraft damage, and accident/incident was significantly lower for all three types of events. The cost investigation are available in the accident database for each of investigation is not represented in the figure, but rather is event included in this study. Appendix L provides more details shown in Table 14. on the calculation of accident costs.