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Suggested Citation:"Runway Deviation Modeling." 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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Suggested Citation:"Runway Deviation Modeling." 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 31
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Suggested Citation:"Runway Deviation Modeling." 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 32
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Suggested Citation:"Runway Deviation Modeling." 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 33
Page 34
Suggested Citation:"Runway Deviation Modeling." 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.
×
Page 34
Page 35
Suggested Citation:"Runway Deviation Modeling." 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.
×
Page 35
Page 36
Suggested Citation:"Runway Deviation Modeling." 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 36

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30 0 1 2 3 4 5 RWY/TWY TWY/TWY RWY/OBJ TWY/TLN TWY/OBJ Type of Separation # of C as es Physical Advisory Circular Facilities capacity Economic Operations capacity Environmental Prior ADG standards Figure 23. Most common justifications for MOS of airfield separations. Aircraft type/weight/wingspan Markings and lighting Dedicated facility use Exemption/order terms 0 1 2 3 4 6 5 RWY/TWY TWY/TWY RWY/OBJ TWY/TLN TWY/OBJ Type of Separation # of C as es Figure 24. Most common restrictions for MOS of airfield separations. Airp. ADG Type of MOS Risk Level Expected # Yrs Risk < 1.0E-7 Risk < 1.0E-09 Expected Severity FAA Risk Classification Acceptable PHL III & IV Taxilane/Taxilane <1.0E-9 N/A Yes Yes Major Low Yes ANC VI Taxiway/Object <1.0E-9 N/A Yes Yes Major Low Yes ADS III Runway/Taxiway 1.0E-7 > 100 Yes No Catastrophic Medium Yes BDR II Runway/Taxiway 1.1E-7 > 100 No No Catastrophic Medium Yes MFV II Runway/Object 5.9E-8 > 100 Yes No Catastrophic Medium Yes N07 I Taxilane/Object 1.2E-9 N/A Yes No Major Low Yes JFK VI Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low Yes EWR V Taxiway/Taxiway Taxilane/Object <1.0E-9 <1.0E-9 N/A N/A Yes Yes Yes Yes Majo r Majo r Low Low Yes Yes MSP IV Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low Yes ORD V Taxiway/Object <1.0E-9 N/A Yes Yes Major Low Yes ORD V Taxiway/Taxiway <1.0E-9 N/A Yes Yes Major Low Yes HYA III Runway/Taxiway 8.8E-8 > 100 Yes No Catastrophic Medium Yes LCI III Runway/Taxiway 2.0E-7 > 100 No No Catastrophic Medium Yes SEA VI Runway/Taxiway 1.6E-6 N/A No No Catastrophic High 1 No 1 SEA VI Taxiway/Taxilane <1.0E-9 N/A Yes Yes Major Low Yes ASE III Runway/Taxiway 9.0E-8 > 100 Yes No Catastrophic Medium Yes ACK III Taxiway/Taxiwa y < 1.0E-9 N/A Yes Yes Major Low Yes ILG IV Taxiway/Object 2.8E-8 N/A Yes No Major Low Yes JYO II Runway/Taxiway 1.2E-7 > 100 No No Catastrophic Medium Yes TAN II Runway/Taxiway 8.0E-8 > 100 Yes No Catastrophic Medium Yes 1MOS approval conditions by the FAA restrict the use of the taxiway under specific conditions to avoid the situation of high risk. Table 12. Summary of results for MOS case studies.

31 The aviation industry is relatively young compared to other industries. Over the past 100 years, rapid technological changes have had a substantial impact on airfield configu- ration and design standards. Airfield standards have been modified to improve safety and to accommodate new tech- nology to improve airport capacity and maintain acceptable safety levels. When the standards are changed to require larger areas and dimensions, existing airports increasingly find themselves constrained by land development and other natural features. Another common situation occurring with airports is the need to have larger aircraft operating at the airport to increase capacity. In this case, the new aircraft may belong to a higher ADG, and the corresponding standards may be different and require larger airfield separations. The methodology developed in this study provides a prac- tical and simple tool to help airports quantify and evaluate risk if they cannot comply with the standards and want to pursue an MOS to submit to the FAA. The methodology is based on lateral deviation studies and models developed in this research as well as in previous studies conducted by the FAA, Boeing, and ICAO. A comprehensive survey of acci- dents and incidents associated with lateral deviations during landing, takeoff, and taxiing operations was conducted to identify causal and contributing factors, as well as to charac- terize the lateral deviation during those events. Major Achievements Airfield Separation Rationale to Develop Standards It is simple to understand the need for airfield separations to avoid aircraft collisions. However, the rationale used by the FAA and ICAO to establish existing standards is not readily available in the literature. This study gathered the information available from FAA and ICAO personnel who were involved in the development or in the management of those standards. The information presented in Chapter 2 herein can be very helpful to the industry and provides documentation that may be used for reference in future studies. Development of Veer-off Accidents and Incidents Database A comprehensive worldwide database of aircraft veer-off ac- cidents and incidents was developed that contains information gathered from existing accident and incident databases and in- formation obtained from other sources (e.g., weather data). The database was developed in Microsoft Access, which pro- vides editing and querying capabilities. The database contains a synopsis of the event, date, location, runway characteristics, characteristics of the aircraft involved, causal factors, conse- quences, and wreckage location/path data. Development of Risk Models for Runway Veer-Offs Risk models for aircraft veer-off during takeoff and landing operations were developed using an approach similar to that presented in ACRP Report 3 for overruns and undershoots (Hall et al., 2008). A two-part model based on the probability of an incident occurring and an estimate of the probability that the aircraft will travel beyond a given distance from the runway edge is used to assess the risk that an aircraft may de- part the existing safety areas. The frequency model is based on operational and weather factors, including a criticality factor that related aircraft per- formance under given conditions with the available distance for operation. The frequency model uses accident, incident, and normal operations data to quantify accident risk factors and provide an assessment of flight risk exposure. C H A P T E R 6 Conclusions and Recommendations

Development of a Tool to Analyze Airfield Separations An analysis process for each type of airfield separation is presented in Appendix A. The procedures are simple to use, and the instructions include practical examples to help the user. The methodology serves as a screening tool to support MOS requests involving airfield separations when the stan- dards cannot be met. The process helps to quantify the risk levels for non-standard conditions and, based on criteria rec- ommended in this report, in agreement with the FAA risk matrix, it is possible to evaluate the feasibility of approval of an MOS request (FAA, 2010). Different procedures are provided depending on the type of airfield separation. It is possible to analyze separations in- volving runways, taxiways, taxilanes, and objects. A specific approach was used for each type of separation. To facilitate the application of the methodology, risk plots are presented for each ADG, and when the analysis involves specific aircraft, risk plots based on wingtip clearance are provided. Recommended Risk Criteria for Taxiway and Taxilane Separations An extensive survey of historical taxiway and taxilane inci- dents helped assess the major factors involved in these events. Due to the slow speeds of aircraft on taxiways and taxilanes as compared to aircraft speeds on runway operations, even under adverse weather conditions or slippery pavements, the pilot was able to stop the aircraft as soon as it departed the paved surface of the taxiway. Further, historical taxiway col- lision events were not related to taxiway deviations. In almost every accident/incident, the collision occurred because there was another aircraft or movable object inside the OFA of the taxiing aircraft. One major conclusion is that the existing standards pro- vide an excellent level of safety and that the risk is lower than one accident in 1 billion operations. Even when another air- craft or object was in the path, resulting in a collision, there has never been a serious injury associated with the accidents, and the damages have been limited mostly to the wingtip of the aircraft. Based on the available evidence, the worst credible conse- quence for a taxiway or taxilane according to the FAA risk matrix is major damage to aircraft and/or minor injury to passengers/workers, major unplanned disruption to airport operations, or serious incident (FAA, 2010). For major con- sequences, the maximum acceptable level of likelihood is “remote.” In this case, a remote event is expected to occur once every year or 2.5 million departures, whichever occurs sooner. Limitations The methodology developed in this study has some limita- tions. Risk of collision between two aircraft, or an aircraft and an object, estimated with this methodology is applicable only to straight parallel segments of taxiways and taxilanes. Although the lateral deviation data in taxiing operations used to develop the risk plots were measured only for the B-747 aircraft, it is assumed that smaller aircraft have lateral de- viation distributions that have smaller ranges. Thus, the model can be considered conservative when applied to smaller air- craft. However, the taxiway deviation models used in this study were developed from lateral deviation data collected on taxi- ways with centerline lights. Therefore, the conspicuity of the taxiway/taxilane centerline is an added risk mitigation measure that should be used when justifying an MOS request. The FAA/ICAO CRM during missed approach was devel- oped based on data for two- and three-engine jet airplanes. The veer-off models developed under this study are based on data from veer-off accident/incident reports taken from several countries and for aircraft with MTOW larger than 5,600 lb. The collision risk during the approach phase of landing is modeled for missed approach during instrument approaches under Cat I and II. This is assumed to be the highest risk con- dition, and the phase when the pilot is under visual condi- tions is not modeled in the risk curves presented. CRM risk is estimated for an aircraft located on the center- line of a parallel taxiway. The taxiing aircraft is of the same ADG as the approaching aircraft, and the maximum tail height for the ADG is taken to characterize the obstacle lo- cated in the taxiway. The same plots may be used to assess risks associated with other types of obstacles at a certain dis- tance from the runway centerline; however, such obstacles must be lower than the maximum tail height of the ADG used to develop the charts. Recommendations for Future Work Effort to Collect Taxiway/Taxilane Deviation Data As described in previous sections of this report, many of the separation standards were developed during World War II and were based on engineering judgment. These standards have helped maintain very high levels of safety, as evidenced by the fact that there is no history of collisions between two aircraft taxiing in parallel routes. With the increase in traffic volume and the need to increase airport capacity, many airports are restricted in their ability to increase existing airfield separations to introduce opera- tion of larger aircraft. Although the FAA permits MOS based on formulas developed for this purpose, the formulas were developed based on engineering judgment, rather than using a probability approach. 32

Recent FAA studies on aircraft deviation for large aircraft have demonstrated the feasibility of collecting data to develop risk models. However, these studies have focused on large air- craft on taxiway segments with centerline lights. There is a need to collect additional data for various categories of aircraft, for both taxiway and taxilane segments, under various environ- mental conditions, with and without conspicuous centerline markings, and with and without centerline lights. Such studies should not be undertaken to modify the cur- rent standards, but they can support MOS processes when the evaluation of shorter-than-standard distances is necessary. Effort to Collect Aircraft Deviation Data during Landing and Takeoff Operations The development of risk plots for the airborne phase of landing used the FAA/ICAO CRM for instrument approach Cat I and II. The CRM model was based on the limited data available at the time it was developed. Aircraft technology and navigational aids have improved significantly since then. As it is expected that airport capacity will need to increase two- or threefold in the near future, it is necessary to develop a more rational approach to more accurately assess the level of safety. Many airports still rely on visual and non-precision approaches, and for these categories, that analysis can be made only by using Part 77 imaginary surfaces obstruction evaluation to obtain a very basic assessment of risk. A risk-based model for the assessment of visual segment or non-precision approaches would benefit many airports in the United States and abroad, particularly for the evaluation of airfield areas. Therefore, studies that address risk assessment for aircraft operations associated with movable or fixed ob- jects within or in the vicinity of airports would greatly bene- fit the aviation industry. 33

34 Glossary of Acronyms AAIB UK Air Accidents Investigation Branch AAIU Ireland Air Accident Investigation Unit AC Advisory Circular ADG Aircraft Design Group AIDS FAA Accident/Incident Data System ANC Ted Stevens Anchorage International Airport AOSC Airport Obstructions Standards Committee ARC Airport Reference Code ARCP Aerodrome Reference Code Panel ASPM Aviation System Performance Metrics ASRS FAA/NASA Aviation Safety Reporting System ATSB Australian Transport Safety Bureau BEA Bureau d’Enquêtes et d’Analyses pour la Sécurité de l’Aviation Civile CAA Civil Aeronautics Administration CG Center of Gravity CIAIAC Comisión de Investigación de Accidentes e Incidentes de Aviación Civil (Spain) CRM Collision Risk Model ETMSC Enhanced Traffic Management System Counts FAAP Federal Aid Airport Program FAR Federal Aviation Regulation FHA Functional Hazard Analysis GA General Aviation ICAO International Civil Aviation Organization IFALPA International Federation of Airline Pilots’ Associations ILS Instrument Landing System ISO International Organization for Standardization JFK John F. Kennedy International Airport LDVO Landing Veer-off MOS Modification of Standards MTOW Maximum Takeoff Weight NAS National Airspace System NASA National Aeronautics and Space Administration

35 NASB Netherlands Aviation Safety Board NLA New Large Aircraft NOAA National Oceanic and Atmospheric Administration NOD Normal Operations Data NPIAS National Plan of Integrated Airport Systems NTSC National Transportation Safety Committee (Indonesia) OCH Obstacle Clearance Height OCP Obstacle Clearance Panel OFA Object Free Area OFZ Obstacle Free Zone RESA Runway End Safety Area ROC Receiver Operating Characteristic RSA Runway Safety Area SARP Standard and Recommended Practice TAIC New Zealand Transport Accident Investigation Commission TERP Terminal Instrument Procedures TOVO Takeoff Veer-Off TSB Transportation Safety Board of Canada USACE United States Army Corps of Engineers

36 Acceptable Level of Risk. For regulations and special per- mits, the acceptable levels of risk are established by consider- ation of risk, cost/benefit, and public perception. Accident. An unplanned event or series of events that results in death, injury, damage to, or loss of, equipment or property. Consequence. The direct effect of an event, incident, or acci- dent. In this study, it is expressed as a health effect (e.g., death, injury, exposure) or property loss. Hazard. The inherent characteristic of a material, condition, or activity that has the potential to cause harm to people, property, or the environment. Hazard Analysis. The identification of system elements, events, or material properties that lead to harm or loss. The term “hazard analysis” may also include evaluation of conse- quences from an event or incident. Incident. A near-miss episode, malfunction, or failure with- out accident-level consequences that has a significant chance of resulting in accident-level consequences. Likelihood. Expressed as either a frequency or a probability. Frequency is a measure of the rate at which events occur over time (e.g., events/year, incidents/year, deaths/year). Probabil- ity is a measure of the rate of a possible event expressed as a fraction of the total number of events (e.g., 1 in 10 million, 1/10,000,000, or 1×10-7). METAR. Aviation routine weather report. Nonconformity. Non-fulfillment of a requirement. This in- cludes, but is not limited to, non-compliance with federal reg- ulations. It also includes an organization’s requirements, policies, and procedures, as well as requirements of safety risk controls developed by the organization. Quantitative Risk Analysis. Incorporates numerical estimates of frequency or probability and consequence. Risk. The combination of the likelihood and the consequence of a specified hazard being realized. It is a measure of harm or loss associated with an activity. Risk Analysis. The study of risk in order to understand and quantify risk so it can be managed. Risk Assessment. Determination of risk context and accept- ability, often by comparison to similar risks. Safety. Freedom from unacceptable risk. Often, safety is equated with meeting a measurable goal, such as an accident rate that is less than an acceptable target. However, the absence of accidents does not ensure a safe system. To remain vigilant regarding safety, it is necessary to recognize that just because an accident has not happened does not mean that it cannot or will not happen. Safety Risk Management. The systematic application of policies, practices, and resources to the assessment and con- trol of risk affecting human health and safety and the envi- ronment. Hazard, risk, and cost/benefit analysis are used to support the development of risk reduction options, pro- gram objectives, and prioritization of issues and resources. A critical role of the safety regulator is to identify activities involving significant risk and to establish an acceptable level of risk. Veer-Off. An aircraft running off the side of the runway dur- ing takeoff or landing roll. Worst Credible Condition. The most unfavorable condi- tion or combination of conditions that it is reasonable to expect will occur. Definitions

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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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