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6 associated with runway operations was based on the evalua- configuration; low friction runway surface conditions (wet, tion of: icy, or contaminated); adverse weather conditions, particu- larly tail wind, cross wind, gusting wind, low visibility, and · The likelihood of the incident occurring; precipitation; and unfavorable runway slopes. Results for · The location where the aircraft came to stop, in case of FHA of aircraft overruns and undershoots are provided in overruns, or its point of first impact, for undershoots; and Appendix B. · The consequences of such an incident (injury and cost of damage). Database Development Overrun and undershoot incidents may be considered in A single database that contains a significant number of rel- terms of the deviation of the aircraft from its intended path. evant accidents and incidents on and near airports was cre- The definition of the deviation for each incident type is sum- ated for this study. A second database comprising normal marized as follows: operations data also was developed for this study. The data were organized to facilitate the assessment of each accident · For overrun incidents, the "longitudinal deviation" is de- type in a coherent manner, rather than based on multiple scribed by the longitudinal distance traveled beyond the databases with different inclusion criteria. accelerate/stop distance available (for takeoff events), and Before data were collected, some criteria were established beyond the landing distance available (for landing events). for filtering out events available in the database sources that · For undershoot incidents, the "longitudinal deviation" is would not be relevant for ACRP 4-01 model development. It described by the longitudinal distance the aircraft under- is important to describe the criteria used and the reasons for shoots the intended runway threshold. applying them. · For both overrun and undershoot events, the "lateral deviation" is the lateral distance to the extended runway Filter Applied to the Data centerline. Some filtering criteria were used on the data so that events Examples of incident and accident causal factors include were comparable, as well as to ensure the models developed human error, as well as incorrect approach speed; deviation would represent the objectives of this study. The first filter of approach height relative to desirable flight path; improper was an attempt to use information from only specific regions touchdown location; inappropriate runway distance avail- of the world having accident rates comparable to the U.S. ability, aircraft system faults, improper weight, and aircraft rate. Figure 2 depicts accident rates by region of the airline Western-built transport hull loss accidents, by airline domicile, 1994 through 2003* Europe C.I.S.1 0.7 JAA - 0.6 United States Non JAA 1.2 China and Canada 0.5 0.4 Middle East 3.1 Asia (Excluding 1.7 China) Africa 13.3 Latin America and Caribbean 2.4 Oceania 0.0 World 1.0 1Insufficient fleet experience to generate reliable rate. Rates per million departures * 2003 Preliminary Information Source: U.S. Department of Transportation, Federal Aviation Administration. Figure 2. Accident rates by region of the world.
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7 domicile. It was assumed that the information from North · Spain Comisión de Investigación de Accidentes e Inci- America (United States and Canada), Western Europe (Joint dentes de Aviación Civil (CIAIAC). Aviation Authorities [JAA] countries), Oceania, and a few selected countries in Asia would be relevant to this study and A more detailed description of each data source is available included in the database. in Appendix C of this report. In addition, the filtering crite- Using this filter criterion, the main sources of data included ria and justification described in Table 1 were applied to the the following: ACRP 4-01 database. · FAA Accident/Incident Data System (AIDS); · FAA/National Aeronautics and Space Administration Data Limitations (NASA) Aviation Safety Reporting System (ASRS); There are many quantitative and qualitative limitations to · NTSB Accident Database & Synopses; reliable accident and incident data, and these limitations in- · Transportation Safety Board of Canada; variably constrain the depth, breadth, and quality of airport · ICAO Accident/Incident Data Reporting (ADREP) system; risk assessments (Piers et al., 1993; DfT, 1997; Roelen et al., · Australian Transport Safety Bureau (ATSB); 2000). This study is no exception. The scope and detail of the · France Bureau d'Enquêtes et d'Analyses pour la Sécurité de analysis are restricted by the availability and quality of the l'Aviation Civile (BEA) ; data extracted from available sources. Major data limitations · UK Air Accidents Investigation Branch (AAIB); found during the collection process are outlined in the fol- · New Zealand Transport Accident Investigation Commis- lowing material. sion (TAIC); · Air Accident Investigation Bureau of Singapore; Missing Data. Accident investigation records and incident · Ireland Air Accident Investigation Unit (AAIU); and reports consist of a number of standard forms and reports. Table 1. Filtering criteria for accidents and incidents. Filter # Description Justification 1 Remove non-fixed wing aircraft Study is concerned with fixed wing aircraft entries. accidents and incidents only. 2 Remove entries for airplanes Cut off criteria for lighter aircraft utilized with certified max gross weight to develop model for overruns on unpaved < 6,000 lbs (<12500 lbs if Part areas. 91). 3 Remove entries with unwanted Some FAR parts have significantly Federal Aviation Regulation different safety regulations (e.g., pilot (FAR) parts. Kept Part 121, 125, qualifications). The following cases were 129, 135 and selected Part 91 removed: operations. Part 91F: Special Flt Ops. Part 103: Ultralight Part 105: Parachute Jumping Part 133: Rotorcraft Ext. Load Part 137: Agricultural Part 141: Pilot Schools Armed Forces 4 Remove occurrences for Keep only undershoots and runway unwanted phases of flight. excursions beyond the departure end of the runway. We are also keeping veer-off occurrences that were available in the Loughborough University database, but these will not be utilized for developing the risk models. 5 Remove all single engine aircraft Piston engine aircraft are now used less and all piston engine aircraft frequently in civil aviation and therefore entries. have been removed, to increase the validity of the modeling. Moreover, single and piston engine aircraft behave differently in accidents due to the lower energy levels involved and the fact that the major focus of this study is air carrier aircraft. 6 Remove all accidents and It would be unfeasible to have an RSA with incidents when the point of first more than 2000ft beyond the threshold, the impact and the wreckage final gain in safety may not be significant and a location is beyond 2000ft from previous FAA study used this criterion threshold. (David 1990).
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8 Even within these standard areas of interest, it is extremely rare However, it should be noted that these data limitations are that every field is complete. The NTSB docket files of minor not unique to the current research but are inherent to risk accidents, when available, frequently contain less than a dozen assessment studies that use historical accident data (Piers, pages of forms accompanied by only a brief synopsis of the 1994; ETSC, 1999). occurrence. Information for incidents is very poor. As an example, prior to 1995, the narratives for AIDS reports were Poor Data Quality. Previous studies using data from limited to 115 characters; reports since 1995 contain a more accident reports and docket files have reported on the poor complete narrative prepared by the investigating inspector. quality of data available (Hagy and Marthinsen, 1987). Erro- neous or conflicting information within the same docket is The accident wreckage site often is given only a very crude not uncommon. Some cases were identified where the pro- description without supporting maps or diagrams. Only a vided wreckage location diagram does not match the text small proportion of data fields are systematically recorded for description given. Confusing and inconsistent use of terms every accident. The amount of missing fields in the database and nomenclature adds to the challenges of extracting precise is high, restricting the number of parameters that could be data points. When faced with conflicting data, the research analyzed with confidence. In many cases the report descrip- team applied judgment to obtain a final figure according to tions used were coupled with the runway satellite picture the best information available. obtained from Google Earth to determine the approximate location of the accident and of the wreckage. Measurement Difficulties. The measurement of certain parameters suffers from inherent ambiguity in the aviation The reports contain mostly information the accident inves- industry. A prime example is runway condition. There sim- tigators deemed relevant to an accident's occurrence. Outside ply has not been an agreed industry standard on reporting of this judgment, few potential risk factors and measurements runway conditions and determining its relationship with are included. This was a major obstacle to developing a data- runway friction and aircraft braking performance (DeGroh base that consistently and systematically records a compre- 2006; FAA, 2006b). The current industry approach is to hensive set of risk exposure parameters so they could be measure and report runway friction periodically using stand- included in the models. The data available for analysis and ard equipment and wet surface conditions. However, it also model-building ultimately depended on the agency accident is common practice to rely on pilots' subjective reporting, investigation mentality and policies. There are no alternative particularly for contaminated runways. Runway surface con- sources of data, and this issue is particularly critical concerning ditions may change rapidly according to precipitation, tem- unconventional or latent risk factors beyond the well estab- perature, usage and runway treatment so actual conditions lished sources of risk. Parameters such as weight and runway may differ significantly from those reported (FAA, 2006b). criticality that would require additional calculation often are Icing conditions, too, also are known to be difficult to deter- impossible to compute because of unavailable data. mine even though they have an important impact on aircraft performance (Winn, 2006). When considering aircraft overruns, there are flights that used more than the nominal runway distance required (take- The weather measured from ground stations may vary sig- off or landing) to complete the operation but without nificantly from that experienced by the accident flight (Jerris departing the runway due to excess runway length available. et al., 1963), particularly if the weather station is located far These cases usually are considered as normal operations and from the accident location, although this is common only with will never feature in accident records. very remote airports. Another difficulty lies in the dynamic nature of meteorological conditions. Wind strength and Although these cases could provide additional and valu- direction may change constantly during the course of an able data to model incident location distribution, obtaining approach. It may not always be clear which reading is most normal operations data on actual runway distance used relevant. Some judgment was necessary to enter the most proved difficult to obtain despite extensive efforts from the appropriate reading into the database. research team. Limited Data for Incidents. The importance of including Finally, the presence of excess runway may alter pilot data from incidents cannot be overemphasized. By excluding behavior such that more runway distance is used than other- incident data, the project would not take into account poten- wise. In a number of occurrences, the pilot did not apply tially serious occurrences. However, a practical difficulty of braking to stop the aircraft as soon as possible because the incorporating incident data is the lack of it. The quantity pilot elected to take a specific taxiway exit or was hurried by and quality of incident data is in even greater doubt than for the traffic control to quickly leave the runway. accidents.
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9 Most agencies provide information and reports for accidents able at the NTSB library in Washington, D.C. Before data and serious accidents only. Many countries have procedures to were gathered, database rules were developed to assure uni- obtain information on incidents but, except for the United formity for the information obtained by different researchers States, these reports are not readily available from Internet contributing to this project. sources. For this study, the basic sources of data for nonserious Incident information was collected from NTSB, FAA AIDS incidents were the FAA AIDS and the NASA/FAA ASRS. and FAA/NASA ASRS databases. Accident data were obtained from NTSB and from aviation investigation agencies from One additional difficulty to incorporate the information other countries. into this project is the number of incidents reported. Some A significant amount of aviation safety information is incidents are not reported because there were no conse- available worldwide, in many cases from specific websites. quences. To overcome this obstacle, a study was performed One of the main problems with this, however, is the frag- on the distribution of available data to assess the number of mentation of the information. Each agency has different unreported incidents and to consider these cases when devel- search engines, and data are presented in different formats. In oping the frequency and location models. A number of miss- most cases, identifying the relevant events fulfilling the crite- ing incidents was assumed, as described in Appendix D, and ria for this project was quite challenging. a weighting factor was applied in the statistical analysis to Appendix E of this report presents the list of relevant acci- develop the models. dents and incidents that fulfilled the criteria and filters estab- lished for the study and were utilized for developing the risk Additional Issues models. The database used for developing the final risk models in- Supplementary Sources of Information cludes only those events that may challenge the RSA beyond the runway ends. The criterion utilized is similar to that used Individual accident reports were evaluated to extract infor- by the FAA (David, 1990) and includes those occurrences mation. In addition, part of the data was complemented from whereby the point of first impact or the final wreckage location other sources of information, particularly for aircraft, airport, is within 2000 ft from the threshold. Using such criteria, 459 and meteorological conditions. Based on the aircraft registra- accidents and incidents were selected to compose the informa- tion, we have gathered information for aircraft involved in tion that was used for developing the risk models. Table 2 sum- accidents and incidents from the following websites: marizes the number and type of events by source of data. The main reason for the criterion applied is it would not be · FAA REGISTRY N-Number Inquiry: feasible to modify an existing RSA to more than 2000 ft in http://registry.faa.gov/aircraftinquiry/NNum_inquiry.asp length, compared to the current 1000-ft standard. Most im- · US/World Landings.com: portantly, the additional safety benefit for having an RSA http://www.landings.com/evird.acgi$pass*90705575!_h- longer than 2000 ft certainly would be very small and not jus- www.landings.com/_landings/pages/search.html tify the costs required for such improvements. Cases when · Airframes.org - Passenger airliners, cargo airplanes, business the aircraft veered off the runway but did not challenge the jets, private aircraft, civil and military. area beyond the runway threshold also were removed, as http://www.airframes.org/ these were out of the scope of this research. · Civil Aircraft OnLine Registers, Official Civil Aircraft Data for events investigated by the NTSB were gathered Registers: from both investigation reports and the related dockets avail- http://www.airlinecodes.co.uk/reglinks.asp?type=Official Table 2. Summary of events utilized in this study. Airport information, when not included in the incident or Database Source LDOR LDUS TOOR accident investigation reports, was obtained from other FAA AIDS (incidents) 14 29 12 sources. Basically the following web sources were utilized in FAA/NASA ASRS (incidents) 79 11 9 this study: NTSB (accidents & incidents) 113 51 56 TSB Canada (accidents) 23 1 5 · United States: AirNav provides detailed aeronautical infor- AAIB UK (accidents) 24 0 5 mation on airports and other information to assist pilots in BEA France (accidents) 3 1 3 Other (accidents) 18 0 2 gathering information for flight planning. Airport details include airport location, runway information, radio navi- Total 274 93 92 gation aids, declared distances, and other information for 459 pilots. http://www.airnav.com