The Air Traffic Control Operational Errors Severity Index: an Initial

DOT/FAA/AM-05/5 The Air Traffic Control Office of Aerospace Medicine Operational Errors Severity Washington, DC 20591 Index: An Initial Evaluation Larry L. Bailey David J. Schroeder Julia Pounds Civil Aerospace Medical Institute Federal Aviation Administration Oklahoma City, OK 73125 April 2005 Final Report This document is available to the public through: • The Defense Technical Information Center Ft. Belvior, VA. 22060 • The National Technical Information Service Springfield, Virginia 22161 NOTICE This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The United States Government assumes no liability for the contents thereof. Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. �� 4. Title and Subtitle 5. Report Date �� 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. �� 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) �� 11. Contract or Grant No. �� 12. Sponsoring Agency name and Address 13. Type of Report and Period Covered �� 14. Sponsoring Agency Code 15. Supplemental Notes �� 16. Abstract �� 17. Key Words 18. Distribution Statement �� 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price �� Form DOT F 1700.7 (8-72) Reproduction of completed page authorized i THE AIR TRAFFIC CONTROL OPERATIONAL ERROR SEVERITY INDEX: AN INITIAL EVALUATION Currently, the FAA Air Traffic Investigations Division Operational Error Severity Index (SI) oversees and coordinates the Operational Error (OE) re- A study of OEs throughout the National Airspace porting process governed by the FAA Air Traffic Quality System (NAS) served as the basis for development of a Assurance Order 7210.56c (FAA, 2002) that details the model that would characterize their severity (Rodgers & conduct of incident reporting processes. The need for a Nye, 1993). Information from the initial investigation formal, system-error reporting program was recognized was used as the basis for development of the current early in the FAA’s evolution. Recommendations were SI. The index is based on the following factors: vertical developed regarding the conduct of incident investiga- and horizontal separation distances, relative flight paths, tions and the use of the resulting information, many cumulative closure rates, and the level of ATC awareness of which were incorporated into the FAA Order 8020 (hereafter referred to as ATC Control). Since these factors (O’Connor & Pearson, 1965). In 1964, a six-month test are based on operationally relevant criteria associated with of an expanded operational error/operational deviation the provision of ATC services, they allow for the calcula- (OE/OD) reporting form was conducted at two en route tion of the severity of air traffic control separation losses. centers located in Miami and Jacksonville, Florida. By July These factors are allocated various point values that total 1965, FAA Order 8020, the AT System Error Reporting 100 and thereby allow for an assessment of relative safety Program, was revised “to provide more complete error oc- across operational errors. currence information and simplify typing with a resultant The current Severity Index formula is computed from savings in time” (League, 1965). In addition to many data that, for the most part, can be objectively determined items resembling those used in the current report, this by post hoc incident investigation. Points are assigned for form included a matrix of points assigned to horizontal varying levels of vertical separation, horizontal separation, and vertical separation. This information was used to closure rate, flight paths, and the amount of control. categorize the event as major, moderate, or minor, using Determination of whether the event was controlled or horizontal and vertical proximity. Although this matrix uncontrolled is the only variable that requires ATC expert was later discontinued, the system was continually revised judgment to determine a point value. to become the current operational error reporting system Vertical and Horizontal separation are defined as the (FAA Order 7210.56c). The error reporting system has minimum separation based on the radar data just prior demonstrated the relatively infrequent nature of OEs. to aircraft divergence. Together, these factors make up For example, in fiscal year 2000 alone, the U.S. air traf- to 50% of the SI point total. As shown in Tables 1a fic system handled 166,669,557 operations with an OE and 1b, the maximum point values (25 points each) are rate of .69 per 1000,000 facility activities. (FAA, 2002). assigned for both vertical and horizontal distances for However, concern has been expressed that the error rate events that culminate in proximities of less than 500 has gradually increased from .49 in 1997. ft vertical and less than 1⁄2-mile horizontal separation. In response to a recommendation in the 2000 report Given existing radar tolerances and measurement tools, by the U.S. Department of Transportation’s Office of further division of minimum separation distance would Inspector General (OIG), the FAA developed a method be of limited value. Accepting the notion that the safety to assign severity values for operational errors that occur in margin decreases geometrically, as opposed to a steady flight. A memorandum of understanding was negotiated arithmetic decline as aircraft get closer, points assessed between the National Air Traffic Controllers Association for close encounters remain higher. Conversely, as vertical (NATCA) and the FAA to support this effort. Having and horizontal separation increase, the potential threat to a tool to group OEs by severity would facilitate the pri- safety is assumed to be lower, and their associated point oritization and allocation of resources to focus attention assignments drop off rapidly. more efficiently on OEs in the different severity groups. When wake turbulence separation standards govern Later, in 2003, an OIG report (hereafter called the OIG aircraft around an airport, SI point values for vertical report) led to a scientific evaluation of the OE Severity separation are not calculated. Instead, in-trail separa- Index (SI) and its component parts. We report on the tions point values are used, as shown at the bottom of results of that evaluation. Table 1b. 1 Respective point values for closure rates and flight paths The following is an example of how the point total were developed to objectively include these parameters is used. If an aircraft is in en route airspace at a higher as components of the Severity Index (Tables 1a-1b). It altitude, standard separation calls for the minimum sepa- should be noted that faster aircraft closure rates, coupled ration to involve either a horizontal distance of 5 miles with converging, opposite-direction flight paths reduce or a vertical distance of 2,000 ft. As separation between the safety margin more so than slower closure rates and aircraft is reduced to less than the required distance, points diverging flight paths. Also, a significant assumption are assigned for the moment when minimum separation is made that aircraft on diverging or non-intersecting occurred. If the aircraft pair was separated by less than paths have little impact on the overall safety margin and 500 ft vertically (25 points) and between 1 to 1.499 miles consequently do not receive Severity Index points. How- (24 points), the subtotal would reach 49 points. At a ever, head-on encounters at high rates of speed, coupled

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