Risk Assessment Method to Support Modification of Airfield Separation Standards (2011)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

25 Variable LDVO TOVO1 Variable LDVO TOVO1 Adjusted Constant 3.088 15.612 User Class G 1.682 2.094 Aircraft Class A/B 0.770 0.852 Aircraft Class D/E/F 0.252 0.091 Visibility less than 2 SM2 2.143 2.042 Visibility from 2 to 4 SM 3 0.808 Visibility from 4 to 8 SM 3 1.500 Xwind from 5 to 12 kt 0.653 0.102 Xwind from 2 to 5 kt 0.091 3 Xwind more than 12 kt 2.192 0.706 Tailwind from 5 to 12 kt 0.066 3 Tailwind more than 12 kt 0.98 3 Temp less than 5°C 0.558 0.988 Temp from 5 to 15°C 0.453 0.420 Temp more than 25°C 0.291 0.921 Icing Conditions 2.67 3 Rain 0.126 1.541 Snow 0.548 0.963 Frozen Precipitation 0.103 3 Gusts 0.036 3 Fog 1.740 3 Turboprop 2.517 1.522 Foreign Origin/Destination 0.334 0.236 Hub/Non-Hub Airport 3 0.692 Log Criticality Factor 4.318 1.707 Night Conditions 1.360 3 1LDVO = landing veer-off; TOVO = takeoff veer-off. 2 SM = statute miles. 3 Blank cells indicate that there are no coefficients associated with these parameters. Where Equipment Class Ref: C Large jet of MTOW 41k-255k lb (B737, A320 etc.) Heavy Acft AB Heavy jets of MTOW 255k lb+ Commuter Acft D Large commuter of MTOW 41k-255k lb (small RJs, ATR42 etc.) Medium Acft E Medium aircraft of MTOW 12.5k-41k lb (biz jets, Embraer 120 Learjet 35 etc.) Small Acft F Small aircraft of MTOW 12.5k or less (small, single or twin engine Beech90, Cessna Caravan etc.) User Class Ref: C = Commercial or F = Cargo or T/C = Taxi/Commuter User Class G G = GA Turboprop Turboprop engine(yes/no) – Ref: Turbojet Ceiling Height feet Visibility statute miles Crosswind knots Tailwind knots Gusts Yes/No – Ref: No Icing Conditions Yes/No – Ref: No Snow Yes/No – Ref: No Rain Yes/No – Ref: No Frozen Precipitation Yes/No – Ref: No Fog Yes/No – Ref: No Air Temperature deg C Turboprop Aircraft Yes/No – Ref: No NonhubApt Yes/No – – Ref: Yes for hub airport Log Criticality Factor If Log(CF) > 0, available runway distance is smaller than required distance Night Conditions Night, Dawn or Dusk – Ref: Daylight Notes: Ref: indicates the reference category against which the odds ratios should be interpreted. Non-hub airport: airport having less than 0.05% of annual passenger boardings Table 7. Independent variables for veer-off frequency models. for each model. Relatively low R2 values are the norm in logis- tic regression (Ash and Schwartz, 1999), and they should not be compared with the R2 of linear regressions (Hosmer and Lemeshow, 2000). A better parameter to assess the predictive capability of a logistic model is the C-value. This parameter represents the area under the sensitivity/specificity curve for Model R2 C LDVO 0.32 0.88 TOVO 0.14 0.82 Table 8. Summary statistics for veer-off frequency models.

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 – (15 – 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 – Wet (W) (iv) Yes/No Dry FW = 1.4 FW is runway distance adjustment factor for wet pavement Runway Surface Condition – Snow (S) (iv) Yes/No Dry FS = 1.6 FS is runway distance adjustment factor for snow- covered pavement Runway Surface Condition – Slush (Sl) (iv) Yes/No Dry FSl = 2.0 FSl is runway distance adjustment factor for slush- covered pavement Runway Surface Condition – 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 – runway contamination factors are those suggested by Flight Safety Foundation (2000) Table 6. Correction factors applied to required runway distance.