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

Chapter: Chapter 3 - Data for Modeling Aircraft Deviations

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Suggested Citation:"Chapter 3 - Data for Modeling Aircraft Deviations." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Page 21
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Suggested Citation:"Chapter 3 - Data for Modeling Aircraft Deviations." National Academies of Sciences, Engineering, and Medicine. 2011. Risk Assessment Method to Support Modification of Airfield Separation Standards. Washington, DC: The National Academies Press. doi: 10.17226/14501.
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Page 20

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Runway Deviation Modeling The probability of aircraft collision associated with the sep- aration between the runway and taxiway or objects depends on whether the movement is a landing or a takeoff operation. For landing there are two types of risk that may be evaluated: • Risk during the final approach phase when the aircraft is air- borne and the combination of large lateral and vertical devi- ations from the nominal approach path may lead to collision with a fixed or movable object in the airfield area (e.g., an aircraft taxiing in a parallel taxiway). • Risk if the aircraft loses directional control after touching down and veers off the runway, colliding with fixed or mov- able objects. These two types of risk may be combined to provide the total risk for landing. The veer-off risk is estimated for every landing operation, whereas the airborne risk is computed only for missed approaches. When taking off, the pilot may reject the procedure and intentionally or unintentionally veer-off the runway. If direc- tional control is lost when in high speed, the aircraft may col- 21 7 98 10 11 12 13 14 15 16 17 Taxilane/Taxilane Wingtip Separation (ft) 1.E-08 1.E-06 1.E-04 1.E-09 1.E-07 1.E-05 1.E-03 R is k of C ol lis io n pe r O pe ra tio n Figure 14. Taxilane/taxilane collision probability based on wingtip separation. 4 86 10 12 14 16 18 20 Taxilane/Object Wingtip Separation (ft) 1.E-08 1.E-06 1.E-04 1.E-10 1.E-09 1.E-07 1.E-05 1.E-03 R is k of C ol lis io n pe r O pe ra tio n Figure 15. Taxilane/object collision risk based on wingtip separation.

20 FAA established separation criteria for taxilanes and taxi- ways and made changes in 1989 (FAA, 1989). These stan- dards are based on aircraft design categories. There is no ref- erence describing the quantitative basis for the criteria, and it is likely that engineering judgment was used to define those standards. Both the FAA and ICAO recognize that aircraft deviations in taxilanes are usually smaller than those occurring in taxi- ways. Aircraft taxiing in taxilanes are moving at very low speeds, and pilots are usually very focused on parking operations in areas where movable objects are common. For the approach presented in this report, the ratios of wingtip separations of taxiway/taxiway to taxilane/taxilane for each ADG were calculated. As shown in Table 5, the ratios var- ied from 0.75 for ADG I to 0.58 for ADG V and VI. These ratios were used to adjust the models used for taxi- way/taxiway separations developed by the FAA. The rationale is that the risk for veering off a taxilane OFA should be simi- lar to or lower than the risk of veering off a taxiway. Therefore, the wingtip to wingtip separation distances associated with each level of risk for taxiways was adjusted using the ratio cor- responding to the ADG. For example, a ratio of 0.58 was applied to the model for lateral deviations on taxiways for ADG V. The resulting model is illustrated in Figure 14. The plot shows the risk trend for taxilane/taxilane separa- tion of ADG V aircraft based on the mean wingtip separation (i.e., based on the wingtip distance when both aircraft are located on the centerlines of parallel taxilanes). The standards for taxilane separations are considered conservative, given the lack of recorded taxilane incidents associated with lateral deviations. Figures similar to Figure 14, based on separation between taxilane centerlines, were developed for each ADG based on the ratios presented in Table 6 and the maximum wingspan for the ADG. Taxilane/Object Separation Similar to the approach for taxilane/taxilane separations, adjustment factors were applied to the FAA/Boeing models for taxiway/object wingtip separations (Scholz, 2003a). The ratios are the same as those used for the taxilane/taxilane model because the standard wingtip separations between two aircraft and between an aircraft and an object are similar according to AC 150/5200-13 (FAA, 1989). The standard minimum wingtip to object separation for ADG V in parallel taxilanes is 31 ft and, based on Figure 15, the risk of wingtip collision is lower than 1.0E-09. 1.E-16 1.E-08 1.E-14 1.E-06 1.E-10 1.E-04 1.E-12 1.E-02 0 10 403020 50 60 Taxiway/Object Wingtip Separation (ft) R is k pe r O pe ra tio n Figure 13. Taxiway/object collision probability based on wingtip separation. ADG Distances in ft Item I II III IV V VI Taxiway/Object Wi ngtip Separation 20 26 34 44 53 62 Taxilane/Object Wi ngtip Separation 15 18 22 27 31 36 Ratio 0.75 0.69 0.65 0.61 0.58 0.58 Table 5. Taxiway/object and taxilane/object mean wingtip separations for aircraft design groups.

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TRB’s Airport Cooperative Research Program (ACRP) Report 51: Risk Assessment Method to Support Modification of Airfield Separation Standards is intended to be used to support requests for modification of standards in those circumstances where the design criteria for separations between taxiways/taxilanes and other taxiways/taxilanes and fixed or movable objects as well as separations between taxiways and runways cannot be met.

The following appendices, included in the pdf and print version of the report, will be helpful in understanding the methodology.

  • Appendix A: Risk Assessment Methodology presents a methodology for five different types of circumstances: taxiway/taxilane to taxiway, taxiway to object, taxilane to taxilane, taxilane to an object, and runway to taxiway/taxilane or object;
  • Appendix F: Aircraft Database Summary presents a summary of aircraft characteristics by model; and
  • Appendix H: Analysis of MOS Cases summarizes information collected in the modification of standards survey and presents results of application of the methodology described in Appendix A to each modification of standards case.

Other report appendices, which are available online only, provide detail and information on the development of the methodology.

In addition, the project developed a

PowerPoint presentation

that may be useful for introducing and explaining the methodology to stakeholders.

In July 2021, an errata was posted for this publication: In Table 7 on page 25, the LDVO coefficient was changed from -3.088 to -13.088. The online version of the report has been corrected.

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