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represent the criticality factor. The greater the value, the more critical the operation because the safety margin decreases, and in many cases strong braking or the possibility of overruns may lead to veer-off events. The distance required is a function of the aircraft per- formance under specific conditions. Therefore, every distance required under International Organization for Standardiza- tion (ISO) conditions (sea level, 15 deg centigrade) was con- verted to actual conditions for operations. Moreover, the dis- tances were adjusted for the runway surface condition (wet, snow, slush, or ice) and for the level of head/tailwind. The adjustment factors for runway surface conditions are those recommended by the Flight Safety Foundation (2009). To summarize, the runway distance required was adjusted for temperature, elevation, runway surface conditions, and wind. Table 6 presents the factors applied to the distance required by the aircraft. A correction for slope was not applied, as this factor had little effect on the total distance required. The use of NOD in the accident frequency model was a major improvement introduced in ACRP Report 3 (Hall et al., 2008), and it was maintained for this study. The analysis with NOD also adds to the understanding of cause and effect rela- tionships for veer-off incidents. Table 7 summarizes the model coefficients obtained for each veer-off frequency model. Table 8 summarizes the parameters representing the accu- racy of each model obtained presenting the R2 and C-values 24 Local Factor Unit Reference Adjustment Factor Definitions Elevation (E) (i) 1000 ft E = 0 ft (sea level) Fe = 0.07 x E + 1 Fe is runway distance adjustment factor for elevation Temperature (T) (i) deg C T = 15 deg C Ft = 0.01 x (T â (15 â 1.981 E) + 1 Ft is runway distance adjustment factor for temperature Tailwind (TWLDJ) for Jets (iii) knot TWLDJ = 0 knot FTWJ = (RD + 22 x TWLDJ)/RD (ii) FTWJ is runway distance adjustment factor for tailwind (jets) Tailwind (TWLDT) for Turboprops (iii) knot TWLDT = 0 knot FTWP = (RD + 30 x TWLDT}/RD FTWT is runway distance adjustment factor for tailwind (turboprops) Headwind (HWTOJ) for Jets (iii) knot HWTOJ = 0 knot FHWJ = (RD + 6 x HWTOJ)/RD FHWJ is runway distance adjustment factor for headwind (jets) Headwind (HWTOT) for Turboprops (iii) knot HWTOJ = 0 knot FTWP = (RD + 6 x HWTOT)/RD FHWT is runway distance adjustment factor for headwind (turboprops) Runway Surface Condition â Wet (W) (iv) Yes/No Dry FW = 1.4 FW is runway distance adjustment factor for wet pavement Runway Surface Condition â Snow (S) (iv) Yes/No Dry FS = 1.6 FS is runway distance adjustment factor for snow- covered pavement Runway Surface Condition â Slush (Sl) (iv) Yes/No Dry FSl = 2.0 FSl is runway distance adjustment factor for slush- covered pavement Runway Surface Condition â Ice (I) (iv) Yes/No Dry FI = 3.5 FI is runway distance adjustment factor for ice- covered pavement i - temperature and elevation corrections used for runway design ii - RD is the runway distance required iii - correction for wind are average values for aircraft type (jet or turboprop) iv â runway contamination factors are those suggested by Flight Safety Foundation (2000) Table 6. Correction factors applied to required runway distance.