Aviation Safety: NASA's National Aviation Operations Monitoring Service Project Was Designed Appropriately, but Sampling and Other Issues Complicate Data Analysis
Published: 2009-03-13T00:00:00

Fast Facts:

Highlights:
section_title: Why GAO Did This Study
paragraphs: The National Aviation Operations Monitoring Service (NAOMS), begun by the National Aeronautics and Space Administration (NASA) in 1997, aimed to develop a methodology that could be used to survey a wide range of aviation personnel to monitor aviation safety. NASA expected NAOMS surveys to be permanently implemented and to complement existing federal and industry air safety databases by generating ongoing data to track event rates into the future. The project never met these goals and was curtailed in January 2007. GAO was asked to answer these questions: (1) What were the nature and history of NASA's NAOMS project? (2) Was the survey planned, designed, and implemented in accordance with generally accepted survey principles? (3) What steps would make a new survey similar to NAOMS better and more useful? To complete this work, GAO reviewed and analyzed material related to the NAOMS project and interviewed officials from NASA, the Federal Aviation Administration, and the National Transportation Safety Board. GAO also compared the development of the NAOMS survey with guidelines issued from the Office of Management and Budget, and asked external experts to review and assess the survey's design and implementation.
section_title: What GAO Found
paragraphs: NAOMS was intended to demonstrate the feasibility of using surveys to identify accident precursors and potential safety issues. The project was conceived and designed to provide broad, long-term measures on trends and to measure the effects of new technologies and aviation safety policies. Researchers planned to interview a range of aviation personnel to collect data in order to generate statistically reliable estimates of risks and trends. After planning and development, a field trial, and eventual implementation of the air carrier pilot survey and the development of a smaller survey of general aviation pilots, the project effectively ended when NASA transmitted a Web-based version of the air carrier pilot survey to the Air Line Pilots Association. NAOMS's air carrier pilot survey was planned and designed in accordance with generally accepted survey principles, including its research and development, consultation with stakeholders, memory experiments to enhance the questionnaire, and a large-scale field trial. The survey's sample design and selection also met generally accepted research principles, but there were some limitations, and the survey data may not adequately represent the target population. Sample frame and design decisions to maintain program independence and pilot privacy complicate analysis of NAOMS data. Certain implementation decisions, including extended methodological experiments and data entry issues, also complicate analytical strategies. Also, working groups of aviation stakeholders were convened as part of NAOMS to assess the validity and utility of the data, but these groups never had access to the raw data and were disbanded before achieving consensus. To date, NAOMS data have not been fully analyzed or benchmarked against other data sources. While NAOMS's limitations are not insurmountable, a new survey would require more coherent planning and sampling methods, a cost-benefit analysis, closer collaboration with potential customers, a detailed analysis plan, a reexamination of the sampling strategy, and a detailed project management plan to accommodate concerns inherent in any survey endeavor. As a research and development project, NAOMS was a successful proof of concept with many strong methodological features, but the air carrier pilot survey could not be reinstated without revisions to address some of its methodological limitations. The designers of a new survey would want to supplement NAOMS where it was self-limiting. Alternatively, a newly constituted research team might lead operational, survey, and statistical experts in extensively analyzing existing data to illuminate future projects. In reviewing a draft of this report, NASA reiterated that NAOMS was a research and development project and provided technical comments, which GAO incorporated as appropriate. NASA also expressed concern about protecting NAOMS respondents' confidentiality, a concern GAO shares. However, GAO noted that other agencies have developed mechanisms for releasing sensitive data to appropriate researchers. The Department of Transportation had no comments.

section_title: Letter
paragraphs: The National Aviation Operations Monitoring Service (NAOMS) was a  National Aeronautics and Space Administration (NASA) initiative that  aimed to develop a methodology to survey a wide range of aviation  personnel to monitor safety in the national airspace system (NAS). The  foundation for the NAOMS project was President Clinton’s August 1996  White House Commission on Aviation Safety and Security, whose  principal charge was to develop, domestically and internationally, a  strategy to improve aviation safety and security. By interviewing a  probability sample of pilots and other aviation professionals, project staff  planned to collect data about the respondents’ experiences and thus make  possible statistically reliable measurements of rates and rate trends on a  wide array of types of safety events in the NAS, from passenger  disturbances to engine failures to bird strikes. Part of a larger NASA  research and development initiative on aviation safety, the NAOMS project  was to demonstrate the feasibility of and develop the capacity for using  survey research to measure the occurrence of safety events. NASA  expected surveys developed under NAOMS to complement existing  federal and industry aviation safety databases. While NASA originally  intended for NAOMS to collect data regularly from air carrier and general  aviation pilots, air traffic controllers, flight attendants, and mechanics and  to hand off the survey data collection to a different entity for permanent  implementation, the project never met these goals.
NAOMS was essentially a survey of air carrier pilots, and it stopped  collecting data in 2004. However, neither project staff nor other aviation  safety stakeholders ever fully analyzed its data. NAOMS was curtailed at  the end of its first and only decade, when NASA transferred a Web-based  version of its data collection system to the Air Line Pilots Association  (ALPA) in January 2007. Where hope had been that the NAOMS project  would provide a comprehensive, systemwide, statistically sound survey  mechanism for monitoring the performance and safety of the overall NAS,  ALPA did not plan to permanently implement the air carrier pilot survey as  it was designed. The data collection system was never fully implemented,  and its future is uncertain.
Our objective in this report is to answer the following three questions:    What were the nature and history of NASA’s NAOMS project?
Was the survey planned, designed, and implemented in accordance with  generally accepted survey principles?
What steps would make a new survey similar to NAOMS better and more  useful?
subsections: section_title: Scope and Methodology
paragraphs: To describe the history and nature of the NAOMS project, we researched,  reviewed, and analyzed related material posted on several NASA Web sites  and provided to us directly by NASA and its contractor for NAOMS. We  reviewed relevant documents on the House of Representatives’ Committee  on Science and Technology Web site. We examined relevant documents  produced by the Battelle Memorial Institute (Battelle), National  Academies, and others as well as information produced for the National  Research Council. In addition, we reviewed a number of relevant reports,  articles, correspondence, and fact sheets on the NAOMS project and air  safety. Many of the publicly available materials we reviewed are named in  the bibliography at the end of this report.
To analyze the NAOMS air carrier pilot survey’s planning, design, and  implementation (including pretest, interview, and data collection  methods); interviewer training; development of survey questions,  including which safety events to include in the survey; and sampling, we  interviewed officials from NASA, the Federal Aviation Administration  (FAA), and the National Transportation Safety Board (NTSB) and NAOMS  project staff. We also reviewed relevant documents. We discussed the  survey with NAOMS team members to obtain their recollections of the  work, particularly regarding limitations, gaps, and inconsistencies in the  documentation. GAO internal experts in survey research reviewed the  Office of Management and Budget’s (OMB) Standards and Guidelines for  Statistical Surveys and derived a number of survey research principles  relevant to assessing the NAOMS survey. We compared the NAOMS  survey’s design and implementation with these principles. Although OMB’s  standards as they are used today were not final until 2006, the vast  majority of OMB’s guidelines represent long-established, generally  accepted professional survey practices that preceded the 2006 standards  by several decades. We also examined the potential risk for survey error— that is, “errors inherent in the methodology which inhibit the researchers  from obtaining their goals in using surveys” or “deviations of obtained  survey results from those that are true reflections of the population.”  Survey error could result from issues related to sampling (including  noncoverage of the target population and problems with the sampling  frame), measurement error, data processing errors, and nonresponse.
We asked three external experts to review and assess the NAOMS air  carrier pilot survey’s design and implementation as well as considerations  for analysis of collected data. These external reviews and assessments  were conducted independently of our own review activities. We selected  the experts for their overall knowledge and experience in survey research  methodology and, specifically, for their expertise in measurement  (particularly the aspects of memory and recall), survey administration and   management, and sampling and estimation. The experts included Robert  F. Belli, Professor, Department of Psychology, University of Nebraska,  Lincoln, Nebraska; Chester Bowie, Senior Vice President and Director,  Economics, Labor, and Population Studies, National Opinion Research  Center, Bethesda, Maryland; and Steve Heeringa, Senior Research  Scientist at the Survey Research Center and Director of the Statistical  Design Group at the Institute for Social Research, University of Michigan,  Ann Arbor, Michigan.
To determine what steps or other considerations might improve the quality  and usefulness of a survey like NAOMS if one were to be implemented in  the future, we identified and described methodological deviations that we  found from GAO’s guidance and OMB’s standards. We also obtained the  views of internal and external experts on how limitations caused by such  deviations might be overcome. We assessed the potential or known effects  of design or implementation limitations we identified.
We focused our review on the most extensively developed part of the  NAOMS effort, the air carrier pilot survey. We discuss the general aviation  study as it relates to the air carrier survey and overall project evolution,  but we do not focus on its development or implementation. We attempted  to identify any problems that might have prevented the NAOMS survey  data from producing meaningful results, and that might not materially  affect the survey results but could result from accepting the reasonable  risk and trade-offs inherent in any survey research project. We note that  limitations may not necessarily be weaknesses.
We conducted our work from March 2008 to March 2009 in accordance  with generally accepted government auditing standards. Those standards  require that we plan and perform the audit to obtain sufficient, appropriate  evidence to provide a reasonable basis for our findings and conclusions  based on our audit objectives. We believe that the evidence obtained  provides a reasonable basis for our findings and conclusions based on our  audit objectives.
section_title: NAOMS Was Intended to Identify Accident Precursors and Potential Safety Issues
paragraphs: The NAOMS project was conceived and designed in 1997 to provide broad,  long-term measures on trends and to measure the effect of new  technologies and policies on aviation safety. Following the 1996 formation  of the White House Commission on Aviation Safety and Security, and the  commission’s 1997 report to the President committing the government and  industry to “establish a national goal to reduce the aviation fatal  accident rate by a factor of five within ten years and conduct safety  research to support that goal,” NASA worked with FAA and NTSB to set  up the Aviation Safety Investment Strategy Team within NASA. This team  organized workshops, examined options, and recommended a strategy for  improving aviation safety and security. One of its recommendations led to  NASA’s Aviation System Monitoring and Modeling (ASMM) project, a  program to identify existing accident precursors in the aviation system and  to forecast and identify potential safety issues to guide the development of  safety technology.
ASMM, within NASA’s Aviation Safety and Security Program, was to  provide systemwide analytic tools for identifying and correcting the  predisposing conditions of accidents and to provide methodologies,  computational tools, and infrastructure to help experts make the best  possible decisions. ASMM was expected to accomplish this by, among  other things:  intramural monitoring, providing air carriers and air traffic control  facilities with tools for monitoring their own performance and safety  within their own organizations, and   extramural monitoring, providing a comprehensive, systemwide,  statistically sound survey mechanism for monitoring the performance and  safety of the overall National Air Transportation System by seeking the  perspectives of flight crews, air traffic controllers, cabin crews,  mechanics, and other frontline operators (NAOMS was developed as the  primary mechanism for collecting this information).
Agencies, airlines, and other private organizations had realized that  quantitative and anecdotal information they had been collecting could not  be used to calculate statistically reliable risk levels. The project team  identified eight major aviation safety data sources that were available  when NAOMS was created. For example, flight operational quality  assurance data could have helped in deriving statistically reliable  estimates from digital measurements of flight parameters, but these data  do not cover all airlines or include information on human cognition or  affect. Another dataset was from the Aviation Safety Reporting System  (ASRS), which for 30 years had been successfully collecting information  from pilots, controllers, mechanics, and other operating personnel about  human behavior that resulted in unsafe occurrences or hazardous  situations. However, because ASRS reports are submitted voluntarily, the  resulting data cannot be used to generate reliable rate estimates. Under  ASRS, pilots describe events briefly by mail or on NASA’s ASRS Web site.  NASA reviews each report and enters detailed information about the  events into an anonymous database that it maintains. According to the  ASRS Director, the system is subject to volatility in reporting, as in 2006,  when the data witnessed a spike in reports of wrong runway use following  a fatal accident in Kentucky, where pilots turned onto a taxiway that was  too short for their aircraft to attain lift-off speed.
Also, ASRS is not statistically generalizable. Although it does not constrain  the types of events that can be reported, ASRS reporting is voluntary and  unlikely to cover the universe of safety events, and it cannot be used to  calculate trends. To complement this system and other safety databases,  the NAOMS project was to interview a statistical sample of professionals  participating in the air transportation system, including pilots, about their  experiences. Data from the interviews were to enable statistically reliable  measurements of rates and rate trends for a wide array of types of safety  events, such as the professionals experiencing fire in the cargo or  passenger compartment or encountering severe turbulence in clear air,  collisions with birds, airframe icing, and total engine failure. As the project  evolved, the NAOMS researchers decided to deemphasize NAOMS’s  potential to calculate rates in isolation, instead highlighting the project’s  primary capability to identify trends worthy of investigation, thereby  complementing other data sources. The premise of the NAOMS project  was that aviation personnel were the best source of information on day-to- day, safety-related events. In measuring the occurrence of safety incidents  that might increase the risk of an accident, rather than accidents  themselves, the project would serve a monitoring role rather than an  investigative role. Instead of directly informing policy interventions, NASA  expected that trends seen in the NAOMS data would point aviation safety  experts toward what to examine in other data systems. However, to date,  the accuracy of rate and trend estimates based on NAOMS data has not  been established.
NASA appointed two researchers with aviation safety experience to lead a  project team in developing surveys for NAOMS as a part of ASMM. The  researchers contracted with Battelle to administer the project. Battelle, in  turn, subcontracted with experts in survey methodology and aviation  safety to help with questionnaire construction and project execution. “1) plausibility and understandability of NAOMS statistics (e.g., reasonable and reliable  representation of the relative frequencies with which unwanted events occur),  “2) stability and interpretability of NAOMS statistical trends,  “3) sensitivity to industry concerns about data misuse, and  “4) timely and appropriate disclosures of NAOMS findings.”
A primary objective of NAOMS was to demonstrate that surveys of  personnel from all aspects of the aviation community could be cost- effectively implemented to help develop a full and reliable view of the  NAS. NASA also sought to find a permanent “home” for the surveys,  having planned to develop “scientific methodologies to maximize the  useful information and minimize the cost, but not . . . provide for  permanent service” or funding for NAOMS.
That is, NASA intended the NAOMS project to collect data continually  from air carrier and general aviation pilots, helicopter pilots, air traffic  controllers, flight attendants, and mechanics. It sought to design a  permanent survey data collection operation that, once implemented, could  generate ongoing data to track event rates into the future (see fig. 1).  NASA was to conduct the research and development steps necessary to  demonstrate a survey methodology that would quantitatively measure  aviation safety throughout the NAS, but it expected that a different  organization, possibly FAA, would permanently implement the surveys  NASA developed.
NAOMS Concept Presented at NASA Data Analysis & Monitoring Workshop Briefings to Aviation Safety Decision Makers NASA’s project leaders outlined these objectives in briefings,  presentations, workshops, and meetings as they explained the project’s  concept and progress (see table 1). The NAOMS team briefed officials  overseeing the ASRS project, for example, on NAOMS’s concept as early  as 1997. In 2005, the team showed the Commercial Aviation Safety Team  (CAST) how the NAOMS air carrier pilot survey could help develop  metrics to assess the effectiveness of safety interventions.
Another early presentation, in March 1998, demonstrated NAOMS’s  concept and goals while spelling out in detail the project’s phase one.  Project staff planned to profile and summarize participant demographics  in a technical document, develop a preliminary statistical design, identify  high-value survey topics, incorporate these topics into a draft survey  instrument, and analyze and validate the survey design to refine the survey  instrument. The presentation delineated four distinct project phases:    develop the methodology, while engaging stakeholder support;    conduct a test survey to prove the concept;  implement the full nationwide survey incrementally; and   hand off the instrument to an organization interested in operating it over  the long term.
Project staff were later to describe the first two stages as one “methods  development” phase. Figure 2 outlines the completion of these phases as  expressed first in 1997 briefings to aviation safety decision makers in the  development stage to the delivery of NAOMS’s data collection system to  ALPA in January 2007. The figure reflects changes in the NAOMS project  resulting from NASA’s decision to halt development of the full array of  surveys indicated in figure 1. By 2004, which was the original target date  for permanent implementation of surveys, the team had been able to  develop and begin only the pilot surveys (both air carrier and general  aviation pilots), not those for other personnel as initially was planned.
As shown in figures 1 and 2, NASA originally planned to end funding in  2004 but extended it to 2007 to “properly fund transition of the data” to the  larger safety community. A Web-based version of the air carrier pilot  survey and related information were handed off to ALPA in January 2007.
subsections: section_title: The Survey’s Development: Feasibility, Methodology, and Field Testing
paragraphs: In 1998, members of the NAOMS team—NASA managers, survey  methodologists, experts in survey implementation, aviation safety  analysts, and statisticians working with support service contractors from  Battelle—began to study long-term surveys that had helped support  government policymaking since at least 1948. The team intended for  NAOMS to employ the best practices of surveys used in other policy areas  providing comparable benefits. The team members reviewed an extensive  variety of surveys used for national estimates and for risk monitoring.  These surveys included the Centers for Disease Control and Prevention’s  Behavioral Risk Factor Surveillance System, which provides information  on, among others, rates of smoking, exercise, and seat-belt use, and the  Bureau of Labor Statistics’ Consumer Expenditure Survey, which provides  data to construct the consumer price index. The team’s aim was to learn  how the NAOMS survey could measure actual experiences. “who were watching the operation of the aviation system first-hand and who knew what  was happening in the field . . .  this use of the survey method was in keeping with  many other long-term federally funded survey projects that provide valuable information to  monitor public risk, identify sources of risk that could be minimized, identify upward or  downward trends in specific risk areas, to call attention to successes, identify areas  needing improvement, and thereby save lives . . . .” “only the aviation systems operators—its pilots, air traffic controllers, mechanics, flight  attendants, and others— the situational awareness and breadth of understanding to  measure and track the frequency of unwanted safety events and to provide insights on the  dynamics of the safety events they observe. The challenge was to collect these data in a  systematic and objective manner.”
In 1999, the team established a plan of action that included a feasibility  assessment, with a literature review, to study methodological issues,  estimate sample size requirements, and enlist the support of the aviation  community. The assessment also planned for research that included a  series of focus groups to help determine likely responses to a survey and a  study of how pilots recall experiences and events. It also outlined a field  trial to begin in fiscal year 1999 and, finally, a staged implementation,  beginning with air carrier pilots, progressing to a regular series of surveys,  and moving on to other aviation constituencies.
For the feasibility assessment, NAOMS researchers consulted with  industry and government safety groups, including members of CAST and  FAA and analysts with ASRS. They reviewed aviation event databases such  as ASRS, the National Airspace Information Monitoring System, and  Bureau of Transportation Statistics (BTS) data on air carrier traffic. The  team drew on information from this research, as well as team members’  own expertise, to construct and revise a preliminary questionnaire for air  carrier pilots. “
What risk-elevating events should we ask the pilots to count?  “
How shall we gather the information from pilots—written questionnaires, telephone  interviews, or face-to-face interviews?  “
How far back in the past can we ask pilots to remember without reducing the accuracy  of their recollections?  “
In what order should the events be asked about in the questionnaire?”
As a result of the 600 air carrier pilot interviews conducted for the field  trial, the researchers decided that telephone interviewing was sufficiently  cost-effective and had a high enough response rate to use in the final  survey. The field trial had tested question content that derived from  previous research and had experimented with the order of different  sections of the survey. The field trial gave the team confidence that the  NAOMS survey was a viable means of monitoring safety information.  However, the field trial did not fully resolve questions about the period of  time that would best accommodate pilots’ ability to recall their  experiences or about the best data collection strategy.
section_title: Getting the Survey Under Way
paragraphs: The team had decided before the field trial that the NAOMS questionnaire  content and structure were to be governed by (1) measures of respondent  risk exposure, such as the numbers of flight hours and flight legs flown;  (2) estimates of the numbers of safety incidents and related unwanted  events respondents experienced during the recall period; (3) answers to  questions on special focus topics stakeholders requested; and (4) feedback  on the quality of the questions and the overall survey process.
After the team analyzed the data from the field trial and conducted further  extensive research, it decided that the NAOMS survey should address as  many safety events identified during its preliminary research as practical,  that its questions should be ordered to match clusters from the field trial  based on causes and phases of flight, and that a sample size of  approximately 8,000 to 9,000 interviews per year would provide sufficient  sensitivity to detect changes in rates. The team structured the survey in  four sections in accordance with their original expectations of what the  survey should cover. NAOMS’s project managers explained the rationale  for this structure, shown in figure 3, in a 2004 presentation to FAA’s Air  Traffic Organization (ATO).
NASA’s contractors began computer-assisted telephone interviewing  (CATI) data collection for the full air carrier pilot survey in March 2001.  Using a sample that was drawn quarterly from a subset of a publicly  available FAA database, interviewers surveyed pilots regularly over  approximately 45 months of data collection. The survey methodology  changed during the first few months of the survey: that is, researchers  settled on which recall period to use and a cross-sectional data collection  strategy approximately 1 year after the operational survey began.  Interviewing ended in December 2004, by which time more than 25,000 air  carrier pilot interviews had been completed.
In addition to the air carrier pilot survey, NAOMS researchers explored  elements of the original action plan for the project. They conducted focus  groups with air traffic controllers and drafted preliminary survey  questions. Building on research done for the main air carrier survey,  NAOMS staff also developed and implemented a survey for general  aviation pilots that ran for approximately 9 months in late 2002 and early  2003. However, by the end of 2002, NASA realized that it would not be  feasible to expand the project to other aviation personnel under its initial  plan to hand off the surveys for permanent service at the end of fiscal year  2004. NAOMS staff focused their attention on establishing the NAOMS air  carrier pilot survey as a permanent service, noting that the system was still  under development and that its benefits had not been fully demonstrated.  They suggested that it would be difficult to find an organization that would  be willing to commit to the financial and developmental resources  necessary to manage an uncompleted project.
section_title: The Survey’s Handoff and Results, and the NASA Inspector General’s Review
paragraphs: NASA’s documentation had repeatedly shown that the NAOMS project’s  purpose was “the development of methodologies for collecting aviation  safety data,” with their eventual transition “to the larger safety  community” for permanent implementation. NAOMS had met its key  objectives of demonstrating a survey methodology to quantitatively  measure aviation safety and track trends in event rates by the end of 2004,  when original funding for the project had been scheduled to end. Seeking  to ensure the future of the survey while streamlining the project, project  staff tested whether Web-based data collection was a cost-effective  measure.
NASA established an agreement with ALPA, which planned to initiate a  Web-based version of the air carrier pilot survey on behalf of CAST and its  Joint Implementation Measurement Data Analysis Team. NASA extended  NAOMS original funding into 2007 to accommodate the transition to  ALPA. NASA conducted training sessions for ALPA staff on the NAOMS  Web application in early fiscal year 2007 and conveyed the operational  data collection system to ALPA in January 2007. However, ALPA never  fully implemented the Web survey. According to an ALPA official in late  2007, the organization was exploring how to modify the survey before  implementing it. Although ALPA never had access to existing NAOMS  data, this official also expressed uncertainty about what should be done  with the existing data. The project effectively ended at the point of  transfer. “demonstrated a survey methodology to quantitatively measure aviation safety, tracked  trends in event rates over time, identified effects of new procedures introduced into the  operating environment, and generated interest and acceptance of NAOMS by some of the  aviation community as described in the Project Plans.”
The OIG report identified several shortcomings of the project, including  that (1) the “contracting officers did not adequately specify project  requirements” or “hold Battelle responsible for completing the NAOMS  Project as designed or proposed”; (2) the “contractor underestimated the  level of effort required to design and implement the NAOMS survey”;   (3) “NASA had no formal agreement in place for the transfer and  permanent service of NAOMS”; and (4) “NAOMS working groups failed to  achieve their objectives of validating the survey data and gaining  consensus among aviation safety stakeholders about what NAOMS survey  data should be released.” An additional deficiency, according to the OIG,  was that, as of February 2008, “NASA had not published an analysis of the  NAOMS data nor adequately publicized the details of the NAOMS Project  and its primary purpose as a contributor to the ASMM Project.”
section_title: NAOMS’s Planning and Design Were Robust, but Implementation Decisions Complicate Data Analysis
paragraphs: We found that, overall, the NAOMS project followed generally accepted  survey design and implementation principles, but decisions made in  developing and executing the air carrier pilot survey complicate data  analysis. We discuss in this report each of the three major stages of survey  development—planning and design, sample design and selection, and  implementation—in turn. While we document the many strengths of the  NAOMS survey and its evolution, we also discuss limitations that raise the  risk of potential errors in various aspects of the survey’s results. We also  note where design, sampling, and implementation decisions directly or  potentially affect the analysis and interpretation of NAOMS’s data.
Table 2 outlines the generally accepted survey research principles, derived  in part from OMB guidelines, that we used in our assessment. The table is  a guide primarily to how we answered our second question on the  strengths and limitations of the design, sampling, and implementation of  the NAOMS survey. However, we caution that survey development is not a  linear process; steps appearing in one section of table 2 may also apply to  other aspects of the project. Direct fulfillment of each step, while good  practice, is not sufficient to ensure quality. Additional related practices,  and the interaction of various steps throughout the course of project  development and implementation, are essential to a successful survey  effort. Table 2 should be viewed not as a simple checklist of survey  requirements, but as guiding principles that underlie the narrative of our  report and our overall evaluation of the NAOMS survey.
subsections: section_title: The Survey’s Planning and Design
paragraphs: Early documentation of the NAOMS project shows that the project was  planned and developed in accordance with generally accepted principles  of survey planning and design. As we have previously discussed, the  project team established a clear rationale for the air carrier pilot survey  and its use for ongoing data collection at its conception. Team members  considered the survey’s scope and role in light of other sources of  available data, basing the questionnaire on a solid foundation of available  data, literature, and information from aviation stakeholders. They devised  mechanisms to protect respondent confidentiality. Researchers collected  preliminary information from focus groups and interviews that they used  in conducting confirmatory memory experiments and in developing the  questionnaire to reduce respondent burden and increase data quality. The  team was also concerned with validating the concept of NAOMS and  achieving buy-in from members of industry and others to help ensure the  relevance and usefulness of the NAOMS data to potential users, although  they were not able to fully resolve questions some stakeholders had in the  utility of the data. The team’s field trial of air carrier pilots allowed them to  answer key questions about data collection and response rate. The field  trial was followed with supplemental steps to revise the questionnaire  before the full air carrier pilot survey.
Notwithstanding the survey design’s strengths, it exhibited some  limitations, such as a failure to use the field trial to fully test questionnaire  content and order and fragmented management plans. We found  potential risk for survey errors involving measurement, with low  implications for risk of error in the survey’s data.
subsections: section_title: Preliminary Research Supported the Survey’s Development
paragraphs: In its planning, the NAOMS team extensively researched survey  methodology, existing safety databases, and literature on aviation safety  and personnel. The team also conducted interviews and focus groups with  pilots. To generate publicity and support from aviation stakeholders, the  NAOMS team made multiple presentations to and conducted workshops  with government officials and aviation stakeholders (see table 1). The  preliminary research and feedback from stakeholders helped the team  define the scope of data collection.
Initial literature reviews focused primarily on the data collection methods  that would be most likely to ensure response accuracy, on question  wording and ordering that would maximize recall validity, and on  preventing respondents from underreporting for fear of being held  accountable for mistakes. A document summarizing several early team  memorandums addressed theories and literature on “satisficing”—or the  notion that survey respondents seek strategies to minimize respondent  burden and cognitive engagement—and the relationship between the data  collection method and respondent motivation. This document, which was  reprinted, in part, in the contractor’s reference report on NAOMS, also  examined literature on social desirability, particularly how confidentiality  affects response accuracy. It included reviews of academic literature on  how interviewing methods can dampen or enhance tendencies toward  socially desirable responses.
The summary document discussed the importance of the questionnaire’s  accounting for memory organization as a way to minimize response  burden and maximize respondent recall using specific cues to take full  advantage of how pilots organize events in memory, thus maximizing their  ability to recall and report events in the reference period. It outlined  specific strategies that have been used to assess memory organization. The  document proposed steps the NAOMS researchers could take to assess  memory organization; identify optimal recall periods; and construct,  validate, pretest, and refine the survey questionnaire. It also outlined a way  to implement and evaluate different data collection methods and included  initial sample size calculations to compare response rates and potential  sampling frames.
Another planning document enumerated in detail the populations of  interest in addition to pilots, including air traffic controllers, mechanics,  dispatchers, and flight attendants. The project team compiled an  annotated list of sources on aviation safety and their limitations to indicate  how the survey might play a role within an overall system to monitor  national airspace safety. The project team supplemented its research with  focus groups and one-on-one interviews with pilots to help in deciding  which safety events the questionnaire should cover. These focus groups  and interviews are discussed in more detail in appendix I.
Workshops and Consultations with Stakeholders and Potential  Users  After presentations on the NAOMS concept and its relevance to aviation  safety in March and November 1998, NAOMS staff held the project’s first  major workshop on May 11, 1999. A wide range of FAA and NASA officials;  representatives from private industry, academia, and labor unions; and  methodologists discussed  the need for NAOMS as a way to fill gaps in safety knowledge and move  beyond accident-driven safety policy (often called the “accident du jour”  syndrome);   government’s and others’ use of survey research, citing specific surveys  that are used to measure rates, trends, risks, and safety information in  other fields; the intent to focus NAOMS questions on individuals’ experiences, rather  than on their opinions; and the need to involve industry and labor stakeholders to ensure high  participation rates and relevant safety content.
In addition to introducing the concept of NAOMS and its likely form, the  team expressly sought labor and industry participation in developing  NAOMS and to ensure high response rates; the relevance of specific  questions; and the survey’s output application to decision making on  policies, procedures, and technology.
Several aviation stakeholders participating in the workshop offered  feedback on the survey in general and on individual questions raised in  focus groups and the early field research. For example, a summary of  comments from FAA staff raised questions about response rate, the scope  of questions, and strategies for data validation. We found that NAOMS  staff clearly thought through many of these issues, including matters of  response rate and questionnaire consistency, and worked to address them  as the project developed. However, as we discuss in the following text,  while NASA initially expected that FAA would be a primary customer of  NAOMS data, it failed to attain consensus with the agency on the project’s  merits and on whether NAOMS’s goal of establishing statistically reliable  rates, in addition to trends, was possible.
Defining the Scope of the Data NAOMS Would Collect  The NAOMS team determined that the NAOMS survey would usefully  supplement other safety resources whose goals were investigative or were  to identify causation. Unlike those resources, NAOMS was to capture not  just incidents but also precursors to accidents and “more subtle  associations that may precede safety events.” The 2007 ASMM summary  report noted that one must know where to look in order to investigate  precursors. NAOMS was designed to point toward such research. The  project team expected that trends seen in the NAOMS data would point  aviation safety experts toward what to examine in other data systems.  Researchers and FAA officials told us that many data, such as radar track  data and traffic collision avoidance data, do not cover the entire NAS and  were not regularly analyzed at the time that NAOMS was being developed.
Following the 1999 workshop on the concept of NAOMS and the  preliminary air carrier pilot questionnaire, a summary of comments from  FAA showed some support for NAOMS. However, the summary expressed  concern that much of the data being gathered were too broad to permit the  development of appropriate intervention strategies. An FAA memorandum  later, following meetings with NAOMS staff in 2003, requested extensive  questionnaire revisions and suggested that certain questions were  irrelevant, should be dropped, or were covered by other safety systems.  FAA also sought more detailed investigatory questions to assess the  causes of some events, such as engine shutdowns, and revisions to  questions that it saw as too subjective and too broad to provide real safety  insight. To ensure that question consistency over time would enable trend  calculations, NASA researchers did not make most of the revisions.  Instead, they responded that to the extent that NAOMS might provide “a  broad base of understanding about the safety performance of the aviation  system” and allow for the computation of general trends over time, its  questions could help supplement other safety systems.
The project team’s concerns about respondent confidentiality influenced  the questionnaire’s design. For example, they expressed some fear that  questions that attributed blame to respondents reporting safety events  would lead to underreporting. These concerns motivated decisions to  exclude from the questionnaire most of the information that could have  identified respondents. Pilots were not asked to give dates or identify  aircraft associated with events they reported. Additionally, the database  that tracked sampling and contact information for individual pilots  recorded only the weeks in which interviews took place, not their specific  dates.
section_title: Project Management Plans Were Not Comprehensive
paragraphs: The NAOMS team’s project management plans were not comprehensive.  From 1998 to 2001, the activities of Battelle and its subcontractors were  covered by statements of work to plan and track the survey’s  development. These documents enumerated tasks, deliverables, and  projected timelines. Similar documents do not exist for the 2002 to 2003  data collection period, when NASA changed priorities for NAOMS. Battelle  developed a new implementation plan to address changes in NASA’s  priorities in 2004, but plans from 2002 onward were largely subsumed in a  series of contract modifications and were not centralized. Twenty-four  base contracts and modifications contained information to track overall  progress, but, according to NASA, the overall ASMM project plan (while in  accordance with NASA policy) did not contain sufficient detail to correlate  the plan with contract task modifications such as those used for NAOMS.  The lack of a central plan makes it difficult to evaluate specific aspects of  NAOMS against preestablished benchmarks. Furthermore, the failure to  maintain management or work plans during data collection or to adapt the  initial work plans to accommodate project changes may have contributed  to the gaps in record-keeping regarding sampling, as discussed later in this  report.
section_title: Innovative Memory Experiments Enhanced the Questionnaire
paragraphs: Research demonstrates that designing a survey to accommodate the  population’s predominant memory structure can reduce respondents’  cognitive burden and increase the likelihood of collecting high-quality  data. The NAOMS team conducted innovative experiments to help in  developing a survey that would reduce respondent burden and  accommodate the air carrier pilots’ memory organization and their ability  to recall events, thus increasing the likelihood of accuracy. While  researching and testing hypotheses about memory organization to  enhance questionnaire design are excellent survey research practices, few  researchers have the time or resources to conduct extensive experiments  on their target population. The NAOMS survey methodologist ran  experiments from 1998 through 1999 to generate and test hypotheses that  could be incorporated into the design of the air carrier pilot survey.
Several of the project’s experiments to determine pilots’ recall and  memory structures were based on relatively few pilots. These were  supplemented with other experiments and additional data analysis to  validate the researchers’ hypotheses. However, these experiments were  limited to the core questions on safety in the air carrier pilot survey and  did not extend to other sections of the survey or other populations,  whether general aviation pilots, mechanics, or flight crew. The memory  experiments led researchers to design the core safety events section of the  survey according to a hybrid scheme of memory organization—that is, it  used groupings and cues related to causes of events as well as phases of  flight, such as ground operations and cruising.
After the memory experiments, the NAOMS survey methodologist  recommended that project staff undertake cognitive interviews to ensure  that the questionnaire to be used in a planned field trial could be  understood and was complete, recommending also that a final version of  the questionnaire be tested with a separate group of pilots. A  memorandum indicated that at least five cognitive interviews were held  before the field trial, but we could not identify documentation on their  effect on the questionnaire’s structure or content.
section_title: A Large-Scale Field Trial Resolved Many Issues, but Not Others
paragraphs: In 1999, following more than 1 year of research, experiments, and  questionnaire development, NAOMS researchers conducted a large-scale  field trial. It was to help decide the appropriate recall period for the survey  questions; major issues of order and content for the questionnaire; and the  appropriate method of survey administration to minimize cost, while  maximizing response rate and data quality. The field trial also allowed the  NAOMS team to assess whether the survey methodology was a viable  means of measuring safety events. Although largely in accordance with  generally accepted survey principles, the field trial had some limitations  and did not resolve important questions about the survey’s methodology.
To administer the trial, team members randomly assigned pilots to various  experimental conditions: three different interviewing methods (self- administered questionnaires, and CATI and in-person interviews), six  different recall periods, and the presentation of the main questions of the  core safety questions first or following the topical focus section.  Interviewers for the CATI and in-person interviews received group and  individual training, and the researchers used widely accepted practices to  enhance response rates for the self-administered questionnaire, with  notifications and reminder letters to maximize response rate. Their  analysis of the data appeared to show that experimental assignments were  sufficiently random and different in data quality to allow some decisions  about response mode and recall period—showing, for example, that  different modes resulted in different completion rates, and that longer  recall periods produced higher event counts.
Recall Period Research and Testing  The NAOMS researchers hoped to reliably measure highly infrequent  events—the severest of which pilots were likely to recall quite well— without jeopardizing the measurement of more frequent, less memorable  events that had safety implications. Literature on survey research did not  point to one specific reference period for events such as those in the  NAOMS survey. To evaluate the effect of recall period on a pilot’s ability to  accurately remember events, the project’s survey expert asked five pilots  to fill out, from memory, a calendar of the dates and places of each of their  takeoffs and landings in the past 4 weeks. Then they were asked to fill out  an identical calendar at home, using information they had recorded in  their logbooks.
The survey methodologist used these data to support his recommendation  that NAOMS use a 1-week recall period, noting that this would require a  substantial increase in sample size to measure events with the precision  NAOMS originally intended. However, because the experiment was  designed to measure only takeoffs and landings—routine activities that  were unlikely to carry the weight in memory of more severe or infrequent  safety events at the heart of the NAOMS project—the survey  methodologist added the caveat that the final decision about recall interval  would have to be informed by the particular list of events in the final  NAOMS questionnaire and the rates at which pilots witnessed them.
Following the logbook experiment, NAOMS researchers tested several  potential recall periods in the field trial, including 1 and 2 weeks and 1, 2,  4, and 6 months. Data from the field trial show an increase in the number  of hours flown and event reporting commensurate with extensions of the  recall period and possible overreporting for the 1-week period relative to  the others. Aside from the logbook experiment, however, no efforts were  made to validate the accuracy of field trial reports of safety events or flight  hours and legs flown in survey data collected within different recall  periods.
The project team also obtained feedback from the pilots participating in  the field trial. This feedback indicated that most who commented on recall  periods said they were too short; the pilots wanted to report incidents that  happened recently, but not within the recall period. The researchers noted  that the pilots’ discomfort with a short recall period did not necessarily  mean the data collected within that period were inaccurate; it meant only  that it was possible that they wanted to report events outside the recall  period to avoid giving the impression that certain events never occurred.  Researchers also studied pilots’ reported confidence in their responses as  an indication of data quality obtained with different recall periods.  However, the information from the field trial tests and respondent  feedback did not resolve the question of which recall period to use.  Researchers decided to use approximately the first 9 months of NAOMS  data collection as an experimental period to resolve questions the field  trial could not answer, and they settled on a 60-day recall period several  quarters after full data collection began.
The contractor administering the field trial randomly assigned pilots to  mail questionnaires, face-to-face interviewing, or CATI. Face-to-face data  collection was stopped after it proved to be too costly and complicated.  The project team then compared the costs and response rates of the two  other methods as well as the completeness of responses as a measure of  data quality. Completed mail questionnaires cost $67 each and had a  response rate of 70 percent, and 4.8 percent of the questions went  unanswered. Telephone interviews cost $85 and attained a response rate  of 81 percent, and all of the questions were answered.
The project team decided that the CATI collection method was preferable,  given the response rate, the cost, and a tighter relationship between the  numbers of hours flown and aggregated events reported. We found ample  information to support this data collection method. In contrast, the field  trial did not provide the researchers with an opportunity to validate the  sample strategy for data collection—either cross-sectional (drawing each  sample anew over time) or panel (surveying the same set of respondents  over time). As with the recall period, researchers used the early part of the  full survey to experiment with both panel and cross-sectional approaches.  They decided on a final data collection approach approximately 9 months  after the full survey began.
Team members developed different versions of the field trial questionnaire  to test whether to survey pilots first about main events—the core safety  issues in section B—or about focus events—the issues on specific topics  in section C (see fig. 3). The researchers’ quantitative analysis of the field  trial data suggested that different section orders did not affect data quality.  However, we found it unusual that the field trial questionnaire did not fully  incorporate the specific question order suggested by experiments or  literature in the main events section. While questionnaires contained  content areas from the memory experiment that combined the causes of  events and the phases of flights, individual topics within the core safety  events section of the field trial survey were not ordered from least to most  severe as the survey methodologist recommended. NASA later clarified  that the NAOMS team incorporated the results of the field trial into the  final survey instrument.
Additionally, the field trial questionnaire did not contain the “drill-down”  questions that appeared in the final questionnaire—that is, questions  asking for multiple response levels (see fig. 4). The failure to include these  questions appears to violate the generally accepted survey practice of  using a field trial to test a questionnaire that has been made as similar as  possible to the final questionnaire. While questionnaires almost inevitably  change between a field trial and their final form, the results of the  experiments, cognitive interviews, and full set of questions should have  been incorporated into the test questionnaire before the development of  the final survey.
In addition to subject matter and survey methodology research,  experiments, and field testing, NAOMS staff used other commonly used  survey research techniques to develop and revise the air carrier pilot  survey questionnaire. For example, we found that at least five cognitive  interviews were conducted before the field trial, but we found no  documentation that described these interviews or their effect. Additional  cognitive interviews were conducted after the field trial on nearly final  versions of the questionnaire before the survey’s full implementation,  resulting in changes to the questionnaire (see app. I). The project team did  not record field trial interviews; doing so would have allowed verbal  behavioral coding, which is a supplemental means of assessing problems  with survey questions for both respondents and interviewers.
Besides the changes the team made to the questionnaire from the results  of the cognitive interviews, team members reviewed the survey instrument  in great detail, adding and deleting questions to make it easier for the  interviewers to manage and for the respondents to understand. However,  as we have previously mentioned, the questionnaire used in the field trial  did not fully incorporate the order of events suggested by the memory  experiments. This order appears to have been addressed after the  cognitive interviewing that took place just before the final survey began.
We found evidence that the NAOMS team made some changes to the  questionnaire as a result of respondent comments on the field trial, such  as discarding a planned section on minimum equipment lists, seen by  many respondents as ambiguous and unclear, in favor of a different set of  questions. However, there is no documentation of additional question  revisions in response to empirical information from the field trial.  Additionally, except for CATI testing involving Battelle managers and  interviewers, we could not find evidence of a pretest of the final  questionnaire incorporating all order and wording changes before the  main survey was implemented. NASA recently told us that the results of  the field trial, as well as inputs from other research, were fully  incorporated into the final survey instrument.
section_title: The Survey’s Sample Design and Selection
paragraphs: We found that for its time, NAOMS’s practices regarding sample frame  design and sample selection met generally accepted survey research  principles, with some limitations. The project team clearly identified a  target population and potential sample sources. To maintain program  independence, the team constructed the sampling frame from a publicly  available database that was known to exclude a sizable proportion of air  carrier pilots, and applied filtering criteria to the frame to increase the  likelihood that the pilots NAOMS contacted would be air carrier pilots,  rather than general aviation pilots. It is not known for certain whether the  approximately 36,000 pilots NAOMS identified for its sample frame were  representative of the roughly 100,000 believed to exist. The implications  for the risk of error were high; the most significant sources of potential  survey error stem from coverage and sampling.
In addition to increasing the risk of error, sampling decisions potentially  affect the analysis and interpretation of NAOMS data. Sample size  calculations may not be sufficient to generate reliable trend estimates  because of the infrequency of events that have great safety significance  and concerns about operational characteristics and potential bias resulting  from the sample filter. Additionally, developing estimates of event counts  for air carrier operations in the NAS (which was not a primary objective of  NAOMS) from a sample of pilots is complicated by the fact that rates from  NAOMS are based on individuals’ reports, rather than on direct measures  of safety events. Also, the survey has the potential for multiple  individuals to observe the same event.
subsections: section_title: Potential Problems Related to the Sampling Strategy Require Additional Assessment
paragraphs: While NAOMS researchers designed and selected a sample in accordance  with generally accepted survey research principles, sampling decisions  they made to address complications influenced the nature of the data  collected. NAOMS’s sampling strategy for the air carrier pilot survey was  complicated by the needs to (1) link a target population to specific  analytical goals; (2) identify an appropriate frame from which to draw a  sample; and (3) locate commercial pilots, rather than general aviation  pilots. Eventually, the team constructed a frame from a publicly available  pilot registration database that excluded some pilots and lacked  information on where pilots worked, compelling the team to use a filter to  increase the likelihood of sampling air carrier pilots. The contractor drew  a simple random sample each quarter from the freshly updated, filtered,  and cleaned database and divided the sample into random replicates that  were released weekly for interviewing. After the first year of the air  carrier pilot survey, which adapted sampling to accommodate experiments  on recall period and panel approach to data collection, the survey sampled  approximately 3,600 air carrier pilots for most quarters of data collection.  This sampling strategy resulted in 25,720 completed interviews by the end  of the air carrier interviewing.
To develop NAOMS’s sampling strategy, the team first needed to identify a  target population. Although an ideal target population corresponds  directly with a specific unit of analysis of interest, researchers often rely  on proxies when they cannot directly sample the unit. With NAOMS’s goal  of estimating trends of safety events per air carrier flight hour or flight leg  in the NAS, a target population might have been all air carrier flights in the  NAS. Theoretically, one could draw a sample of all air carrier flights in the  NAS, locate the pilots on these flights, and interview them about events  specific to a particular flight.
Given that such a sample would be prohibitively resource-intensive, the  NAOMS team identified an alternative target population—namely, air  carrier pilots. Surveying air carrier pilots would provide information on  safety events as well as on how many flight hours or flight legs that pilots  flew. If the frame fully covered the population of air carrier pilots, the  team’s planned simple random sample from the frame would allow an  estimation of individual air carrier pilots’ rates of events experienced per  hour or leg flown. In isolation, these individual-based estimates would fall  short of cleanly characterizing the NAS, which involves other pilots  besides air carrier pilots and other personnel, including other crew  members on each flight. However, the estimates could address NAOMS’s  goal of estimating rates (for individual air carrier pilots) on the basis of  risk exposure and trends in safety events over time, to supplement other  systems of information about safety.
One potential difficulty with this target population was that the number of  pilots actively employed as air carrier pilots was not known when the  project began. Although the NAOMS team extensively reviewed the size of  the pilot population, we found multiple estimates of the target population  from the NAOMS documentation. NAOMS’s preliminary research  suggested that approximately 90,000 pilots were flying for major national  and regional air carriers and air cargo carriers. Other information  suggested that the population could have been as large as 120,000 pilots.  For example, the 60,000 air carrier pilots in ALPA’s membership  represented “roughly one-half to two-thirds” of all air carrier pilots, or,  alternatively, up to 80 percent of the target population. In light of these  different estimates, we assume for purposes of discussion a target  population of about 100,000 air carrier pilots.
NAOMS researchers next needed to identify a source of information on its  target population to provide a sampling frame from which it could sample  air carrier pilots. As we have previously mentioned, because there was no  central list of air carrier pilots that would ensure coverage of the target  population, researchers had to choose an alternative frame. Initially, they  considered using ALPA’s membership list of air carrier pilots. However, to  maintain the project’s independence and to be as inclusive of pilots as  possible, regardless of their employer or union status, they decided against  using this or any other industry list, such as personnel information from  airlines.
The project team also considered using FAA’s Airmen Registration  Database. Its information on pilots included certification type and  number, ratings, medical certification, and other personal data. When the  survey was first being developed, limited information for all pilots in the  Airmen Registration Database was publicly available as the Airmen  Directory Releasable File. In 2000, after the field trial but before the full air  carrier pilot survey was about to be implemented, FAA began allowing  pilots to opt out of the publicly releasable database. NASA officials told us  that the team had considered asking FAA for the full database but decided  against formally pursuing access to it for several reasons. These included  ensuring continuing access to a public, updated database; ensuring access  to a database that contained contact information for pilots; and  maintaining independence from FAA as an aviation regulatory agency.  Also, NASA was concerned about using the full data, because it wanted to  maintain the privacy of pilots who had removed their names from the list  explicitly to avoid contacts from solicitors, purveyors, or the like.
NAOMS staff had access to the full database when it was still publicly  available in 2000 for the air carrier pilot survey’s field trial sample.  However, NASA officials believed that they could not use it for the full- scale survey from 2001 to 2004 because the nature of the frame—in terms  of how well it represented the current air carrier pilot population—would  change over time. Instead, the team decided to use as the frame for the  full-scale air carrier pilot survey the Airmen Directory Releasable File that  excluded pilots who had opted out; this file was regularly updated over the  course of the air carrier pilot survey. The choice of frame may have been  appropriate, given programmatic constraints, but posed several  challenges. First, pilots in the publicly available Airmen Directory  Releasable File were not necessarily representative of pilots in FAA’s full  Airmen Registration Database. Second, the database lacked information  on whether airmen actively flew for a commercial airline. Lastly, only a  relatively small portion of the 688,000 pilots in the database at the time of  the field trial were air carrier pilots.
Potential Effect of the Opt-out Policy  NAOMS staff, realizing the potential limitations of using the publicly  available data, were concerned about whether the frame provided  adequate coverage of the target population or introduced bias into the  data—that is, whether pilots in the public, opt-out database were  sufficiently representative of air carrier pilots overall. For example, ALPA  had provided its membership (which comprises approximately two-thirds  of air carrier pilots) with information about the opt-out policy and with a  form letter to pilots to facilitate their removal from the list. It is, therefore,  possible that ALPA pilots removed their names from public access at a  higher rate than non-ALPA pilots.
NAOMS researchers’ analysis suggests that air carrier pilots may have  removed their names from the public database at a disproportionately  greater rate than did general aviation pilots. One Battelle statistician  expressed concern to other NAOMS team members that the sample,  therefore, might not represent the population of interest. To help assess  potential bias as a result of the opt-out policy (and the filter, discussed in  the following text), researchers added a question to the survey—part way  through the data collection phase—asking pilots to identify the size  category of the aircraft fleet of the air carrier for which they flew. This  information would allow for a comparison with air carrier fleet sizes  known to exist in the NAS.
Identifying Air Carrier Pilots from the Sampling Frame  The database from which the project drew its sample of pilots lacked  information on where the pilots worked and, therefore, could not be used  to identify pilots flying commercial aircraft. The incidence of air carrier  pilots in the full Airmen Registration Database was fairly low— approximately one in seven pilots would have been an air carrier pilot.  (We could not find documentation on the number or proportion of air  carrier pilots in the opt-out database, but we believe it to have had a  similarly low incidence.) Therefore, the NAOMS researchers decided to  use a filter to increase the likelihood that those contacted for the survey  would be air carrier pilots.
The filter required that pilots be U.S. residents certified for air transport,  with flight engineer certification and a multiengine rating—a rating that  sets specific standards for pilot experience and skill in operating a  multiengine aircraft. By construction, all pilots in the public (opt-out)  Airmen Directory Releasable File who did not fulfill these filtering  requirements fell into the sampling frame to be used for the general  aviation survey. After the filter was applied, the final frame for air carrier  sampling had approximately 37,000 pilots in the first several quarters;  records on the size of the frame’s later quarters were not maintained.
With these filtering criteria, approximately 70 percent to 80 percent of  those contacted for the air carrier sample were, in fact, air carrier pilots  who had flown within the recall period specified on the questionnaire.  Although the contractor collected some information on pilots who were  contacted but deemed ineligible for the survey, the data were not analyzed  specifically to establish how effective the filter was at identifying air  carrier pilots, even if they did not qualify for the survey. Without data on  which people were excluded because they were general aviation, rather  than air carrier pilots, these pilots would be wrongly omitted from the  sampling frame for the general aviation survey.
As data collection progressed, the NAOMS team realized that the data  were biased toward more experienced pilots, pilots flying primarily as  captains, and pilots flying widebody aircraft over longer flight times.  After extensive analysis of the observed bias, the team attributed the bias  primarily to two of the four filtering criteria—that is, that pilots were  required to have both air transport and flight engineer certifications. Team  researchers explored various strategies for addressing the observed bias  and made several recommendations for data collection and analysis. The  team considered whether using stratification to select samples according  to alternative or additional characteristics would help reduce the observed  bias toward more experienced pilots flying larger aircraft, but it eventually  decided against changing the sampling strategy midsurvey.
To determine whether the filter systematically excluded certain types of  respondents—for example, air carrier pilots flying smaller aircraft or pilots  with less experience—the NAOMS team recommended capitalizing on the  implementation of NAOMS’s general aviation portion. The sampling frame  for the general aviation survey included all pilots not filtered into the air  carrier sample. Accordingly, project staff could examine the  characteristics of air carrier pilots who fell into the general aviation  sample because they did not meet filtering requirements, to establish  whether they differed notably from those surveyed using the filtered  sample. Preliminary analysis confirmed that pilots surveyed from the  filtered sample exhibited systematic differences from air carrier pilots in  the general aviation survey. Specifically, pilots surveyed with the air  carrier sampling filters overrepresented captains and international flights,  underrepresented smaller aircraft and airlines, and overrepresented the  largest aircraft and airlines.
Following these analyses, the NAOMS team advocated incorporating  operating characteristics into all analyses to mitigate potential bias. For  the most part, the team recommended using operational size categories— that is, small transport aircraft and medium, large, and widebody  aircraft—to stratify and possibly weight analyses, since different types of  aircraft face different event risks and since safety issues may be more or  less serious, depending on operating characteristics or aircraft make and  model. The team’s presentations of preliminary results frequently  incorporated such analyses, as shown in figure 5. While other operational  stratifications were suggested, such as specific aircraft make and model, it  was acknowledged that this kind of analysis would dramatically reduce  the effective sample size available for analysis in each category. A smaller  effective sample size would decrease the precision of estimates from the  survey, making it more difficult to detect changes in rates over time,  especially for infrequent events.
Additionally, to the extent that the data were to be analyzed as rates per  flight leg or flight hour, an analysis segregated by operational  characteristics would represent a fair description of these rates if it were  assumed that the data adequately represented aircraft and pilots  experiencing safety events within those operational categories—for  example, if the widebodies and their pilots in the sample were fairly  representative of air carrier widebody aircraft and pilots in the NAS.
section_title: Sample Size Calculations May Have Curtailed Statistically Reliable Trend Estimates for All Questions
paragraphs: NAOMS aimed to generate statistically reliable rates and trends that would  allow analysts to identify a 20 percent yearly change with 95 percent  confidence. However, the ability to detect such trends depended not only  on the sample size, but also on the frequency of events. One statistician  who had worked with the project team reported recently that detecting  changes in trends of very rare events, such as complete engine failure,  would require a prohibitively large sample of approximately 40,000 pilots.  NAOMS’s sample sizes were insufficient to allow analysis of all questions  on the air carrier pilot survey or to accommodate analytical strategies that  researchers eventually deemed necessary after data collection had begun,  such as analysis by aircraft size category.
During the field trial, sample sizes were calculated to distinguish response  rates between the three data collection methods (face-to-face and  telephone interviews and mail questionnaires) to answer questions such as  the following: Did an 81 percent completion rate for telephone interviews  differ significantly from a 70 percent response rate for mail  questionnaires? Later sample calculations for the full survey focused more  directly on establishing the ability to detect a 20 percent change in event  rates over time. Data from the field trial were analyzed to estimate how  frequently an air carrier pilot experienced each specific event, enabling the  team to assess how reliably different sample sizes could detect increases  or decreases of 20 percent. From the field trial data, the contractor  estimated that 8,000 interviews would allow detection of changes in rates  with 95 percent confidence for approximately one-half of the core safety  event questions.
The team eventually settled on a sample size of approximately 8,000 cases  a year, declaring in its application to OMB that this would be the minimum  size required to reliably detect a 20 percent change. The application  clarifies that just 5,000 unique pilots would be interviewed in the first year  to gather 8,000 completed surveys (4,000 in cross-sectional samples, and  1,000 in four waves of the panel), but sample size calculations submitted to  OMB do not expressly consider the impact of the panel’s smaller sample  size on the ability of NAOMS data to detect trends. In the 3 years after  data collection experiments in recall and method were discontinued, the  survey interviewed approximately 7,000 cases a year.
At the time the NAOMS OMB application was submitted, project staff did  not have adequate data to know for certain how frequently individual  safety events would be reported, or to know an exact number of  interviews that could actually be attained in a year. The NAOMS OMB  application reported that pilots experience certain events quite  infrequently, without expressly calculating how well a sample size of 8,000  could generate reliable estimates for such events. The sample size  calculations in the application also assumed that the first-year data could  be aggregated across recall periods and both the panel and cross-sectional  data collection approaches that were used. NAOMS project staff later told  us that further analysis would be essential to establish whether rates and  trends generated from different recall periods and data collection  approaches were sufficiently similar to allow combining the data. NASA  believes that, even without data from the experimental period, the  subsequent 3 years of air carrier pilot data were sufficient to demonstrate  the survey’s capability of detecting trends reliably.
Partway through data collection for the full air carrier pilot survey, NASA’s  contractor conducted simulations using early NAOMS data to better  establish sample sizes at which 20 percent changes in rates for individual  questions could be detected. These data confirmed that a sample of 8,000  cases a year would be sufficient to detect a 20 percent change for roughly  one-half the core safety event questions, assuming all cases were analyzed  simultaneously. By this point, however, the project team had already  established the importance of breaking out NAOMS’s estimates according  to the size category of the aircraft flown to compensate for operational  differences and the effects of the sampling procedures that we have  previously described. Thus, sample size calculations may have overstated  the ability of the NAOMS data to reliably detect trends at given  significance levels, if segregating answers by operational characteristics is  critical. Additional simulations that accounted for likely analytical  considerations would be essential to determine whether the NAOMS  project could attain its goal of measuring 20 percent changes in rates of  different safety events with statistical confidence.
section_title: Sampling and Design Decisions Bear on NAOMS’s Rate Calculations and Characterization of the National Air Space
paragraphs: When analyzing NAOMS’s data, researchers must consider the effect of  several design and sampling decisions that the project team made to  accommodate pilots’ confidentiality and the infeasibility of directly  sampling all flights in the NAS. For example, the likelihood that a  particular event would be reported by a pilot responding to the NAOMS  survey increased with the number of crew witnessing the event and the  number of aircraft involved. However, in designing a questionnaire to  lessen the likelihood of respondent identification, the NAOMS team  decided not to link pilots’ reports of specific events to particular aircraft  flown during those events or on the dates on which those events  happened. Furthermore, the team’s choice of sampling frame and filter  resulted in a disproportionate selection of captains relative to other crew  members. While sampling and design choices were rational in light of  concerns about confidentiality and program independence, such decisions  have had implications on how to calculate and interpret rates from  NAOMS and on whether analysts can extrapolate the data to characterize  the national air space. NAOMS staff failed to identify specific analytical  strategies to accommodate these issues in advance of data collection.
Using NAOMS Data to Calculate Rates and Trends  Survey design and sampling decisions affect how rates from NAOMS data  can be calculated. For example, the NAOMS survey has the potential to  collect multiple reports of safety events if more than one crew member on  an aircraft or crew members on different aircraft observed the same safety  event. Safety events happening on aircraft with more crew members  would also have had a greater likelihood of being reported, since more  individuals who experienced the same event could have been subject to  selection into the sample. These issues are not a problem, unless  researchers fail to address them appropriately in an analysis.
Analytic goals must determine whether one adjusts for the potential that  an event is observed by multiple crew members in the sampled population.  Given that one of NAOMS’s goals was to characterize the rate at which  individual air carrier crew members experienced events per flight hour or  flight leg, and assuming all crew members in an aircraft were equally likely  to be sampled, multiple crew members observing an event involving one  aircraft would not pose a problem. However, other considerations bear on  whether and how to make adjustments. For example, bias resulting from  the sampling frame and filter suggests that captains were more likely to  have been selected into the air carrier sample than first officers or other  crew members; additionally, many pilots flew in more than one crew  capacity during the recall period. Events involving multiple aircraft also  complicate estimates, partly because individuals not qualified for the air  carrier pilot survey might have flown many of these aircraft. Extrapolating  from individually derived rate estimates to system counts would also  require making substantial assumptions and adjustments (see the  following text).
One potential strategy to address the possibility of multiple observations  of the same event would be to allocate events according to the number of  crew members who might have witnessed them (more details on  alternative strategies are in app. I). For example, a report of a bird strike  from a pilot flying a widebody aircraft with two additional crew members  could be counted as one-third of a bird strike. Appropriate allocation  presumes, however, that the analyst can identify the number of crew  members present for any given report of a safety event. In general, the  NAOMS recall period extended over 60 days, during which some pilots  flew two or more types of aircraft of different size categories, implying  different numbers of crew. Additionally, the questionnaire did not allow a  pilot who flew more than one aircraft to identify which aircraft a reported  safety event was associated with or in which role he or she served as crew.  Analysts seeking to address the potential effect of multiple reports of the  same event would have to develop allocation strategies that account for  these design issues.
Researchers must also develop allocation strategies for other aspects and  types of analysis using NAOMS data, such as trends or rate estimates for  different aircraft types. We have previously mentioned that the NAOMS  team recommended analyzing data by operational size category because of  sampling considerations and because the effect and exposure to certain  risks varied by class of aircraft. They also noted the importance of  seasonal variations in relation to safety events—for example, icing is less  likely to be a problem in summer than winter.
In its preliminary analysis, the NAOMS team attempted to resolve the issue  of seasonal assignment by using nonproportional allocation strategies. The  team used a midpoint date of the recall period—for example, October 1 if  an interview recall period ran from September 1 to October 30—to  determine a seasonal assignment for each interview in the analysis. For  pilots flying different aircraft during the recall period, team members  assigned an operational size class, based on the aircraft predominantly  flown. For pilots who reported flying different operational sizes of aircraft  equally over the recall period, project staff used a random number  generator to determine the size class for preliminary analysis.
Extrapolating to the National Airspace System  The NAOMS team disagreed on the survey’s ability to provide information  on systemwide event counts versus rates and on trends based on  individuals’ risk exposure. In preliminary analysis, the contractors often  used BTS data to weight NAOMS data to generate systemwide event  counts for air carrier operations in the NAS, and to provide baseline  measures to assess potential bias resulting from sampling and filtering  procedures. Since BTS’s data collection processes changed during the  NAOMS data collection period, however, the contractor stopped using  these data to weight its estimates.
Because of the distinction between the NAOMS’s unit of analysis and the  sampling frame, as well as other sampling issues we found, it may not be  possible to establish systemwide event counts for air carrier flights from  the NAOMS data without using an external benchmarking dataset.  However, extrapolating to systemwide event counts was not an explicit  goal of the project. To the extent that analysts seek to use an external  dataset to weight the NAOMS data in estimates of systemwide counts, that  dataset’s collection procedures and reliability would require assessment.  Additionally, caution should be exercised, since changes in data collection  or editing procedures over time could confound actual trends with  changes resulting from variations in any external weighting dataset.
section_title: The Survey’s Implementation
paragraphs: We found that NAOMS researchers followed generally accepted survey  principles for many aspects of the survey’s implementation, with some  limitations. Sample administration, information systems, and  confidentiality provisions appear to have been adequate, and telephone  interviewers were successful in administering technical questions and  attaining high completion rates. However, despite adequate records of  data editing and checks, analysis and interpretation of NAOMS data are  complicated by first-year experiments in recall period and data collection  approaches and CATI programming choices, along with sampling and  design decisions. Researchers did not conduct full data validation or  nonresponse bias assessments to ensure the quality of the data. We found  deficiencies in record-keeping and moderate implications for the risk of  survey error; the potential survey errors involved processing, sampling,  and nonresponse.
subsections: section_title: Information Systems and Sample Management Maintained Confidentiality, but Data Checks and Record- Keeping Were Limited
paragraphs: We found several issues with NAOMS information systems. Sample  administration and management, including notification of and  informational materials for pilots and release of sample for interviewing,  met generally accepted survey principles. Pilot confidentiality seriously  concerned project staff, and steps to protect confidentiality appear to have  been adequate. In contrast, CATI programming and data checks, along  with record-keeping, had greater limitations.
Taking its sample from the Airmen Directory Releasable File, NAOMS  sampled using pilots’ certificate numbers, with a filter designed to target  air carrier pilots. After adjusting for duplicate certificate numbers that had  entered the sample some time in the previous year (regardless of whether  an interview was completed), the team obtained pilots’ updated addresses  from the U.S. Postal Service’s change-of-address file and submitted them  to Telematch to obtain telephone numbers for each address. This process  resulted in an approximately 60 percent match of addresses to telephone  numbers, which researchers saw as sufficient because they believed the  Airmen Directory included some records for individuals who had retired  or were deceased. Each quarterly sample was then divided randomly into  13 parts to be released weekly. On the Friday before each week’s release,  project staff sent pilots a notification on NASA letterhead that described  the study and its confidentiality provisions and informed them that an  interviewer would be calling. To pilots for whom Telematch could not  provide a valid telephone number, or who had “bad” numbers from the  field trial, project staff sent postcards asking them to call NAOMS  interviewers directly or to send in an updated telephone number.
The project team monitored the disposition of the sample on a weekly or  quarterly basis, including the proportion of respondents who were  ineligible, refused, or could not be located. While between 17 and 29  percent of pilots in each quarterly sample could not be located, and  consequently were not interviewed, approximately 5 percent of the  completed interviews resulted from cases that had not been matched to a  telephone number through Telematch. The NAOMS team aimed initially  for a 6-week fielding period, or “call window,” to allow interviewers  sufficient time to call back each nonresponding pilot in the sample before  assigning the case a final disposition (such as “no-locate” or “refusal”) and  removing the pilot from the sample. However, researchers found that a   3-month call window was necessary to attain a sufficient response rate.  The team did not indicate having compared the answer patterns of pilots  they reached early in the sample with the answer patterns of pilots who  were hard to track down, to ensure the patterns were comparable across  the full sample field period.
Information Systems and Pilot Confidentiality  The survey’s management techniques and documentation for interviewers  indicate that the NAOMS project team was particularly attentive to  confidentiality. The questionnaire did not ask pilots to link safety events to  specific flights, airlines, or times. Interviewers were informed that  “Battelle  not link data items with individual pilots. All reports will be  presented using aggregate information.” Battelle used separate systems  to track the sampling and to store the interview data, which ensured that  pilots’ answers could not be linked to any identifying information. In the  system with sampling information, the specific date of each interview was  not recorded, only the week in which it happened. The NAOMS Reference  Report described NAOMS’s responses as “functionally anonymous” and  suggested that the promise of confidentiality enhanced the respondents’  rapport with the interviewers. “
The identity of respondents will not be revealed to anyone outside of the study staff.  “
The data presented in reports and publications will be in aggregate form only.  “
The respondent will be assured that participation is completely voluntary and in no way  affects their employment.”
Among analytical products for the aviation community, researchers  planned to release summary reports and “structured, fully de-identified  datasets.” According to a presentation at the first NAOMS workshop,  NAOMS products would be subject to FOIA after they were in “a finished  state.” NASA officials told us that they agreed that there would be little  risk of violating pilots’ confidentiality if data were released in aggregate as  initially was planned.
In meetings with NASA, as well as in the agency’s written comments  responding to our draft report, officials expressed serious concern about  the importance of protecting pilots’ identity, a concern we share. The  officials offered several specific examples of how they felt NAOMS data  could be used to identify individual pilots. However, many government  agencies that collect sensitive information, such as the Institute for  Education Sciences, the Census Bureau, and the National Center for  Health Statistics, have successfully allowed individual researchers access  to extremely sensitive raw data on individuals. These agencies have  effectively addressed the issue of individual privacy by, for example,  requiring researchers to attain clearance to use data that could reveal  sensitive information, to sign nondisclosure agreements, and to submit to  stiff penalties for noncompliance. Additionally, agencies may restrict the  types of analyses that can be performed with the data, where data can be  analyzed, and how the data are reported. For example, the National Center  for Health Statistics may prevent researchers from accessing table cells  that contain fewer than five observations to lessen the likelihood that an  individual respondent can be identified.
We realize that given the evolution of data mining techniques, one could  conceive of a full, raw NAOMS dataset being linked to proprietary  information from airlines or a host of other safety systems in ways that  might enable a dedicated data analyst to identify a particular pilot from the  air carrier survey. This breach seems unlikely to happen, however, given  the relative absence of identifiable information in the survey data and the  lack of connection between the tracking database and the CATI data. If the  survey were to be implemented as it was planned and the data released  publicly only in aggregate, the confidentiality provisions of the air carrier  pilot survey appear to have been adequate. The risk that individual pilots  might be identified from the raw data would be greater for the general  aviation survey, which involved a wider range of aircraft types, several of  which might be linked to very small populations of pilots.
NASA officials also expressed concern that pilots might have understood  NAOMS’s promises of confidentiality as conferring the kind of legal  protection that voluntary reporting to a system like ASRS provides. We  found no evidence substantiating or refuting this understanding. To the  extent that confidentiality protections in NAOMS were adequate, any fear  that pilots would invoke legal protections that did not exist are unfounded.
CATI Programming and Data Checks  Partly because NASA emphasized the importance of not second-guessing  pilots, and partly because project staff wanted to avoid truncating answers  unnecessarily, the contractor built only limited edit checks into the CATI  data collection system, despite initial plans to the contrary. The  questionnaire used in training interviewers identified one structured  prompt for the number of hours a pilot reported having flown during the  recall period. It did not include any other instructions to recheck values  reported for specific questions if they seemed unreasonable (perhaps  indicating mistyping or an interviewer-respondent misunderstanding).
Although the contractor documented edits and quality checks that it  performed on the collected data, the CATI system may not have included  all initially planned edit checks. The final questionnaire for interviewer  training suggests that additional edit checks were built into the CATI  system, but the contractor’s data editing protocols suggest that the edit  checks were not consistently integrated into the program. For example,  when pilots were asked to break the time that they flew different aircraft  into percentages—such as 50 percent of the time flying a Boeing 737, 25  percent flying a McDonnell Douglas MD-80, and 25 percent flying a Boeing  727—the CATI system was supposed to have forced interviewers to  reenter information if the responses did not add to 100 percent. Therefore,  if, for example, the interviewer had mistakenly entered 25 percent for each  of the three separate aircraft categories, the total percentage (75 percent)  should have triggered the CATI system to force the interviewer to reenter  information until it added to 100 percent, but the system did not in a  handful of cases. Although such anomalies were extremely rare in the air  carrier pilot data, multiple managerial reviews and tests of the CATI  programming before the survey was implemented failed to identify the  anomalies in advance of survey fielding.
For many of the questions that pilots were asked, the concern that  answers not be truncated unnecessarily by imposing predetermined edit  checks seems reasonable, given that the goal was to generate statistically  reliable information on aviation safety that was otherwise unavailable. For  other questions, such as those on total engine failure and other rare  events, input from aviation experts and operational staff would have  helped in constructing thresholds for the checks in the CATI system. The  additional data would have helped analysts distinguish between true  outliers and data entry errors and between interviewer and respondent  misunderstandings.
Survey completion rates were relatively high, and the NAOMS team  reported exceptionally few break-offs partway through the interviews. It is  impossible to know for certain whether the high completion rates were  because interviewers did not second-guess pilots by asking them to repeat  answers that researchers had deemed unlikely. To the extent that  interviewer rapport with pilots was enhanced because the pilots were not  second-guessed, the decision to limit the number of built-in CATI edit  checks may have enhanced the completion rates, at the expense of  complicating data cleaning and outlier identification.
NAOMS record-keeping was fairly decentralized. While many of the  individual steps of the NAOMS project appear to have been documented in  some form, the project staff and contractors did not assemble a  coordinated, clear history detailing the project’s management that would  facilitate evaluation of the overall air carrier pilot survey. Information on  the project’s steps is largely dispersed across a series of contracts and  modifications between NASA and Battelle and internal NAOMS team  documents on individual pieces of the project. The lack of summary  documentation for various aspects of the project makes it difficult to   (1) distinguish between what was planned at the beginning of the project  and what phases were accomplished in later years, following NASA  priority changes for NAOMS’s resources, and (2) assess whether aspects  of project and budget management raised the potential risk of survey  error.
Regarding the sample, the contractor kept limited information on the size  of the frame before and after filtering to identify air carrier pilots. The size  information the contractor maintained was not enough to reconstruct the  sampling fraction—the percentage of pilots sampled each quarter from the  filtered frame—for all quarters of the air carrier pilot survey. Additionally,  Battelle’s procedures for maintaining pilot confidentiality aimed to make it  extraordinarily difficult to identify which pilots were in the sample frame  at any given time. At the time of sampling, Battelle maintained enough  information to remove pilots who had already been sampled from future  samples for the next four quarters. Battelle did this partly because the  population was relatively small, and because they did not want to  interview the same pilot more than once a year. Although the contractor  lacked formal records, it estimated that the procedure led to the exclusion  of approximately 20 percent of the filtered sampling frame in any given  year.
Regarding NAOMS data, the lack of sampling records prevents analysts  from leveraging sampling information when producing estimates or  calculating sampling errors. Furthermore, the lack of these data hinders  the kinds of nonresponse bias analysis that the project team originally  planned. Without reliable information on the proportion of cases that were  removed from the sample in any given quarter, analysts must rely on more  conservative variance estimates than might have been necessary, making  the detection of changes over time more difficult.
section_title: Experiments in Data Collection and Recall Period Length May Have Restricted the Utility of the First-Year Data
paragraphs: Two main experiments that NAOMS researchers conducted in the initial  year of interviewing may have restricted the utility of first-year data.  Because the field trial had not resolved the optimal length of time the  survey’s questions should cover, researchers used the final survey to test  first two and then three different recall periods for several months. Subject  matter experts on the team also advocated a second experiment to  determine the relative merits of a panel or cross-sectional data collection  approach. NASA officials told us that they viewed the first months of the  survey as part of a development phase, rather than full implementation of  the survey. Nevertheless, NAOMS project staff have noted that adequate  research on the feasibility of combining data from the experimentation has  not yet been done. Depending on the results of such research, it may be  imprudent to evaluate NAOMS’s first-year responses as if they were similar  to the trend data collected in subsequent years. Approximately one- quarter of NAOMS air carrier pilot survey interviews were collected under  experimental conditions; the subsequent 3 years of the survey used a  cross-sectional data collection approach with a 60-day recall period. “We will be asking panel members to give us a code word that we can use to link  interviews, but this code word will not be kept in our tracking system. Pilots forgetting the  word will not have their data linked.”
The NAOMS team decided to begin its first full year of air carrier data  collection using both panel and cross-sectional approaches.
After analyzing the first half-year of data, the team noted that, among other  things, the panel approach may have heightened pilots’ awareness of the  timing of safety events but not the number of events recalled. The project  team decided, for the following four reasons, to abandon the panel design  in favor of cross-sectional data collection: (1) the panel design resulted in  fewer independent observations; (2) the panel design was logistically  difficult to administer; (3) NAOMS’s confidentiality procedures made  analyzing repeated observations over time impossible (the proportion of  pilots who remembered the password and thus could have data linked was  not reported); and (4) the cross-sectional design had yielded a sufficiently  high response rate to allay worries that pilots would be unwilling to  respond unless enlisted as panel members.
As we have previously discussed, the lack of literature on pilots’ recall, in  particular, and the wide variation in the literature’s recommended recall  periods, more generally, made it difficult for the team to decide on the  most appropriate recall period. Team members had extensively analyzed  data from the field trial to determine any differences among the recall  periods tested in that survey. Researchers’ analysis showed that, as  expected, respondents with longer recall periods reported having flown  more hours and legs than those with shorter recall periods. Researchers’  regression analysis also confirmed a positive relationship between recall  period and the total number of events that pilots reported; the magnitude  and statistical significance of this relationship was strongest between 2  weeks (14 days) and 2 months (60 days). Additionally, the team examined  pilots’ comments on whether their particular recall period had been  appropriate.
Despite these analyses, the team decided to delay the decision on recall  period until they had collected more data in the initial months of the full  air carrier survey. After reviewing the field trial results and pilots’  comments, the team was firm only in the belief that a 7-day period was too  short, despite a small-scale experiment suggesting this period was optimal  for pilots’ memory of routine events. (However, a 7-day period would have  been too short to capture infrequent risk events.) The team explored  various tolerances for error, event periodicity, and cost before testing   30-day and 90-day recall periods in the survey’s first two quarters of  sampling.
After the first two waves of data collection, team members explored data  on the length of the recall period. Then they tested a three-way split  design, collecting an additional 2 months of cross-sectional data to assess  whether 60 days would be the best compromise between the 30-day and  90-day periods. Using these data, the project team compared the mean  event rate over time across all core safety event questions—noting that  longer recall periods should result in pilots reporting more events—and  the standard deviation associated with these rates, which declined as the  recall period increased. However, the team did not analyze the  relationship between recall periods and specific events or the correlation  of exposure units (flight hours and flight legs) to safety events for the  different periods. Eventually, staff chose 60 days as providing a  reasonable balance between the recall of events and avoidance of error.  According to NASA officials, the selected recall period was seen as a  compromise between cost and reliability. Despite the theoretical merits of  the analyses justifying this decision, researchers cannot independently  confirm the accuracy of reporting under different recall periods without  separate data validation efforts as part of the field trial or full survey.  However, the practicality of efforts to validate respondent accuracy  depends on the nature of the data being collected, the existence of  alternative data sources, and the design of the questionnaire. As NAOMS’s  survey methodologist has observed, surveys would be unnecessary if a  true population value were known.
Because NASA’s objective in designing and implementing the NAOMS  survey was to develop a data collection methodology, the team was  warranted in deciding to use the first year of data analysis to resolve  questions that had not been fully answered by the field trial. This is  particularly true for their decision to test various recall periods that would  help them find an appropriate balance between recall period and budget  and sampling constraints. As we have previously mentioned, further  analysis would be required to establish whether data collected during the  experimentation can be combined with later data using only the 60-day  recall period and cross-sectional approach. However, NASA officials told  us that the subsequent 3 years of cross-sectional data collection with a   60-day recall period was sufficient to demonstrate the capability of the air  carrier pilot survey to measure trends.
section_title: Experienced Professional Interviewers Administered Technical Questions
paragraphs: Training materials, questionnaire copies and revisions, specificity in  interviewers’ scripts, and cooperation among staff demonstrate that the  team selected appropriate interviewers and was sensitive to key issues  throughout the questionnaire’s development. The NAOMS project team  decided not to use aviation experts as interviewers in the belief that the  “lack of expert knowledge can be a benefit since the interviewers are only  recording what they hear rather than interpreting it through the lens of  their own experiences.” To mitigate issues that might have resulted from  using interviewers unfamiliar with the subject matter, the team  emphasized the importance of the clarity of the questions and consistency  in how the interviewers read them and responded to the respondents’  questions.
The project staff emphasized the importance of using professional and  experienced interviewers and giving them adequate training to administer  the survey. NAOMS’s principal investigator told us that the interviewers  Battelle used for the NAOMS survey were exceptionally professional and  were accustomed to conducting interviews on sensitive topics.  Interviewers received a training manual for the project’s first year, which  included the following: a background on the rationale for the NAOMS  survey, a description of how the survey could shed light on safety systems,  the survey’s confidentiality protections, and information on the survey’s  sampling and tracking information. They also received a paper copy of  the questionnaire with interviewer notes, pronunciation information, and a  glossary of aviation terms.
The NAOMS team conducted a series of cognitive interviews with pilots to  learn whether they would understand the questions and whether the  incidents they reported were those that the team sought to measure. These  interviews led to questionnaire revisions to address potential ambiguities  for both respondents and interviewers. Regardless of efforts to develop  clear questions that interviewers could read directly and respondents  could easily interpret and answer, the team acknowledged that certain  questions turned out to be less reliable than others. For example, in  considering a question series on the uncommanded movements of  rudders, ailerons, spoilers, and other such equipment (see fig. 6), the  team’s concern was that pilots might be unaware of these events or might  interpret uncommanded movements as including autopilot adjustments.  The survey instrument did not include instructions to interviewers to  clarify the intended meaning of this set of questions, and question  standardization alone could not overcome the questions’ potential  ambiguity, despite interviewers’ skill.
In its quality assurance procedures, Battelle monitored and documented  approximately 10 percent of the interviews. However, it did not record  audio of the interviews. Battelle’s documentation states that the  monitoring procedure took the form of live supervisory monitoring of  interviews in progress, as well as callbacks to respondents to ask about  their interviewing experience and to administer key questionnaire items  again to see whether answers were reliable. However, NASA officials told  us that the callbacks were never performed, in keeping with the project’s  concerns about pilot confidentiality.
section_title: Telephone Interviews Attained High Completion Rates, but Validation Efforts Focused Primarily on Face Validity
paragraphs: While interviewers for NAOMS attained high completion rates from pilots  in the sample, limited validation efforts hinder confirmation of data  quality. Roughly 80 percent of sampled pilots thought to be eligible for the  NAOMS air carrier pilot survey completed telephone interviews, and a  notable portion of those who were contacted were found to be ineligible.  The project team decided against conducting nonresponse bias analysis  and did not pursue other formal data validation, focusing instead on the  face validity of preliminary NAOMS rates and trends.
In public presentations and documents of air carrier pilot survey results,  NAOMS staff often discussed the rate of sample cases that were located  and the proportion of interviews completed. The completion rate, distinct  from a response rate, surpassed 80 percent by the end of the air carrier  survey. Throughout the air carrier survey, approximately 23 percent of  those contacted were deemed ineligible because they were not  commercial air carrier pilots or had not flown in the recall period.  Additionally, approximately 24 percent of cases drawn for the air carrier  sample were never located and, thus, their eligibility for the sample could  not be determined.
A survey’s response rate, defined, in general, as the number of completed  interviews divided by the eligible number of reporting units in the sample,  is often used as an indicator of data quality and as a factor in deciding to  pursue nonresponse bias analyses or additional survey follow-up. OMB’s  guidelines, although not yet formal when the NAOMS survey was  implemented, call for a nonresponse bias analysis when survey response  rates fall below 80 percent. OMB guidelines cite survey industry standards  for response rate calculations; these calculations generally include either  unknown sample cases or an estimate of likely eligibles among unknown  cases, in the denominator of the calculations. A calculation of response  rates that excludes unknown cases rests on the assumption that all of  those cases would have proven ineligible. For NAOMS data, a response  rate calculation that included cases of indeterminate eligibility in the  denominator (because the pilots could not be located) would be closer to  64 percent. If the cases not located fell out of scope at approximately the  same rate as the cases that were located and contacted, the NAOMS  response rate would be approximately 67 percent.
NAOMS staff told us that they decided against pursuing nonresponse bias  analyses as initially planned because they thought that air carrier  completion rates were quite high for pilots who were located and  contacted and because NASA’s priorities had changed, resulting in fewer  resources for staff to complete such activities. However, more  conservative calculations of response rates might have merited further  scrutiny, such as a nonresponse bias analysis or other research into  reasons for the sample rate of unlocated pilots. Comparing information  from the sample frame respondents’ and unlocated pilots’ characteristics  might have provided insight into any systematic differences between the  two groups.
NAOMS project staff attempted to validate the data in a variety of limited  ways. Besides the interview monitoring, they made preliminary  calculations, such as a comparison of the hourly rate at which pilots left  the cockpit to deal with passenger disturbances. They found that, unlike  some other events, the rate dropped dramatically after September 11, 2001  (see fig. 7), which demonstrated the importance of enforcing existing rules  requiring the cockpit door to be closed during flight. Other validation  attempts included checking on the seasonality of events—for example, on  whether reports of icing problems increased in winter.
The NAOMS staff recommended more formal validation efforts, suggesting  the examination of questions that had been included in the survey  specifically because they could be benchmarked against other FAA data  systems, such as ASRS and the Wildlife Strike Database. Such work would  have been complicated, however, by the decision to use NAOMS data to  fill in data gaps from other safety systems and not to ask questions that  directly overlapped them, even for items included for benchmarking. For  example, NAOMS asked pilots about all bird strikes without establishing a  threshold for their severity. FAA does not, however, require pilots to  report all bird strikes to its Wildlife Strike Database, only those bird  strikes that cause “significant” damage. Additionally, aviation researc have estimated that up to 80 percent of bird strikes with civil aircraft are  not reported to FAA’s Wildlife Strike Database. Therefore, it is not  surprising that NAOMS data imply a much higher incidence of bird st than other systems.
In addition to considering examples such as pre- and post-September 11,  2001, rates, NAOMS staff had also examined other issues that had intuitive appeal, such as seasonal fluctuations in reported bird strikes. Project  staff also suggested that the data corresponded well with other data  systems, citing as an example both runway incursions—a decline in w the NAOMS team attributed to an FAA policy change—and reserve fuel  tank use—an increase in which had reportedly been seen in ASRS.  Additionally, for field trial data, project staff examined the strength o relationship between the number of events reported and the hours flown  or the length of the recall period, because pilots flying more hours or  recalling events over longer recall periods should report more events t those with fewer hours flown or shorter recall periods. In addition to  having face validity, the survey methodologist noted that the relationsh between events reported and flight hours and legs is also a measure of  construct validity, in that it demonstrated that NAOMS’s measures  corresponded well with theoretical expectations. However, the  relationship does not confirm whether the events that pilots repo rted  actually happened. No other data validation efforts were undertaken o n  the full survey. NAOMS project staff reported that several questions in  ip  the NAOMS data had face validity, but the data still had to be  benchmarked. While such benchmarking is critical for validating NAOMS  data, it may not be sufficient to confirm the accuracy of pilot recall for  most NAOMS questions or to estimate the potential effect of nonresponse  bias.
section_title: Stakeholders Disagreed on the Utility and Value of the NAOMS Data
paragraphs: The effectiveness of NAOMS as a monitoring tool depended on its ability  to provide reliable and valid estimates to address customers’ concerns.  NAOMS team members promoted the survey’s potential for generating  rates and trends but also debated whether the data could be used to  establish baseline counts of events for the NAS. NAOMS working groups  were started but disbanded before resolving this issue or benchmarking  the data against what was known from other safety data.
NAOMS Data and Systemwide Event Counts  NAOMS team members agreed that the survey was designed to measure  the occurrence of events, rather than their causes. They did not clearly  agree on the survey’s ability to provide systemwide counts of events,  rather than rates per flight hour or flight leg, or rate trends over time.  According to the project’s leaders, NAOMS was never intended to generate  an absolute picture of the NAS (i.e., total counts of the number of events in  the NAS each year). They told us that its utility was understood to lie in its  ability to measure relative frequencies that could be used to generate  trends over time. However, NASA’s OIG found “a disparity between the  stated goals of NAOMS and the manner in which NAOMS project  management initially presented the data to FAA,” a point that FAA also  raised. Senior FAA officials told us that NAOMS staff repeatedly  indicated that the project would provide “true” estimates of rates of safety  events in the NAS at the project’s beginning, a capability that FAA  disputed. NAOMS’s emphasis on relative trends, which FAA believed  NAOMS could depict, happened only in later stages of the project.
Regardless of whether NAOMS data were presented as counts or rates, the  data were never designed to serve as a stand-alone system. The survey’s  methodologist told us that he believed that NASA staff were always clear  about the goal of establishing rates and trends, but that in the absence of a  baseline count of how frequently safety events occurred, these rates were  insufficient to specifically quantify change from the survey’s beginning.
However, in theory, such data could be used to generate trends if the  nature of any sampling and nonsampling error in data collection remained  constant over time.
Additionally, the NAOMS survey methodologist described issues that  might jeopardize inferences about trends based on hourly rates. For  example, because rates per-exposure unit are a per-pilot measure, rather  than a system or aircraft measure, one could incorrectly attribute a change  in rates to a systemwide shift that might instead have resulted from a  change in technology that affected the number of individuals in the  cockpit crew. As we have previously mentioned, the sampling frame, the  filter, and potential noncoverage and nonresponse issues would make  further analysis necessary before one could conclude that NAOMS’s  measures of rates per-exposure unit could be generalized to the full  population of air carrier pilots.
According to NASA’s researchers, when the NAOMS contractors began to  work closely with the data, they began to extrapolate and generate  systemwide count estimates. NASA reported that one contractor believed  it was essential to report system counts: that is, counts were necessary to  convey the meaning of the data from a policymaker’s perspective and rates  did not convey the significance of a given result. Battelle staff used BTS  data to weight NAOMS data according to systemwide numbers of flight  hours or flight legs and used these estimates in several presentations of  NAOMS preliminary results. The staff reported to us later that they had  decided against weighting up to the full population of aircraft types  because they did not think that it made sense to combine operational size  categories of aircraft.
The early presentations of the NAOMS data raised concerns for FAA,  because the numbers presented as systemwide estimates did not match  FAA’s other information sources. Several FAA and NASA officials with  whom we spoke asserted that data from several specific survey items did  not correspond with the content of other reporting systems. However, the  items cited were not intended to overlap directly with data FAA had  already collected. NASA officials conceded that how NAOMS defined the  question wording might have contributed to one cited discrepancy. In  addition, FAA officials thought NAOMS was unable to accurately measure  systemwide rates of safety events and asked for extensive, specific  revisions to the survey to address specific questions. Among other things,  these officials wanted NAOMS to ask questions that were more  investigatory in nature than the broad monitoring concept that NASA had  envisioned. NASA did not make the changes that FAA recommended part  way through the survey. In correspondence with FAA, NAOMS researchers  emphasized that the survey’s ability to measure trends required consistent  question wording. FAA officials were also concerned about the quality of  NAOMS data because the survey’s questions were based solely on pilots’  perceptions.
NAOMS’s Working Groups  NASA’s project leaders reported that the working groups were to play a  critical role in evaluating the validity of the NAOMS data and in  establishing whether the survey’s information seemed reasonable, given  what was known about safety from other data sources. The two working  groups, established in 2003 and 2004, were distinct from the two  workshops conducted in 1999 and 2000, although the groups and  workshops were similar in that they both aimed to introduce the NAOMS  project to a wide range of stakeholders, including FAA and industry  members, and that they solicited input on the survey’s goals and  questionnaires.
NASA envisioned a wide range of participants in the working groups,  including pilots; flight attendants; people familiar with alternative data  systems; and other aviation stakeholders, such as academic researchers  and industry. Project leaders told us that they did not expect that  participants would necessarily attain consensus, except to the extent that  the groups thought the NAOMS data appeared to be valid and could  publicly present the data in a way that would not be automatically  translated into systemwide extrapolation of event counts. According to a  presentation at the first working group meeting, in December 2003, “the  release of NAOMS data, and its future directions, will be guided by the  Working Group .” NASA and FAA representatives had agreed earlier  that year not to release any survey results before the working groups  reviewed them and came to a consensus on the timing, content, and level  of the release of NAOMS data.
Discussing the fate of the 2003 and 2004 working groups, NASA’s OIG  concluded in March 2008 that “the NAOMS working groups failed to  achieve their objectives of validating the survey data and gaining  consensus among aviation safety stakeholders about what NAOMS survey  data should be released.” The working groups’ limited effect may have  stemmed partly from disagreement over their composition. NASA project  leaders suggested that FAA had wanted an existing advisory group to  oversee efforts to validate the data, whereas NASA wanted a different  combination of academicians—specifically, FAA staff, subject matter  experts, and industry stakeholders. FAA officials told us that they had  serious concerns about some of NASA’s proposed experts, because these  experts cited preliminary estimates from NAOMS data that FAA found not  to be credible.
Additionally, portions of the working group agendas were dedicated to  discussing the importance of survey research for reliably measuring  trends. These discussions might indicate that some working group  members doubted the core foundations of the NAOMS project or the  survey’s ability to supplement aviation safety systems. According to an  official in NASA’s OIG, he believed that the presentations at the working  groups were, in a sense, an attempt to get the working group participants  on board with the NAOMS project.
NASA’s project team suggested that the two working group meetings took  place necessarily late in the NAOMS project to allow for the collection of  enough preliminary data and to work through nondisclosure issues. The  team also suggested that the meetings “were largely dedicated to  organizational, procedural, and membership issues.” Moreover,  presentations at the two working group meetings showed only the  contractor’s preliminary aggregate analysis. Because the working group  members never had the raw data, they had no opportunity to achieve  consensus on the validity of NAOMS data or appropriate uses of these  data. NASA’s project leaders have asserted, moreover, that the “Working  Group approach” was “terminated prematurely because the NAOMS  resources were re-directed to another approach.” According to the  project leaders, policy changes resulted in the disbanding of all advisory  groups before a more formalized NAOMS group could be assembled after  the first two groups failed to reach their objectives. Reestablishing any  sort of advisory group would be difficult, because NASA procedures would  require prospective participants to undergo a strict nondisclosure  procedure.
Given that the working group members did not have access to the raw  data and did not agree on the groups’ goals or composition, it is not  surprising that they were unable to productively pursue consensus on the  validity and utility of NAOMS data. Additionally, to the extent that some  participants rejected NAOMS’s premise that a survey is a valid and reliable  way to generate safety-related data, they are not likely to have believed  that the data the project collected could be validated. For example, while  acknowledging that NAOMS had the potential to allow reliable estimates  of relative trends, FAA officials told us that they disagreed that NAOMS  could generate statistically reliable rate estimates because of the  subjectivity of NAOMS questions. These officials questioned the ability of  NAOMS’s information to generate rates or its capacity for validation by  existing databases. Additionally, FAA officials noted that they did not  believe any potential customers would have confidence in aggregate  NAOMS results unless the source data were released to the customers  directly, rather than to a working group. FAA also expressed concern that  pilots would lack causal knowledge to answer the survey’s questions.  However, we have noted in this report that the questionnaire was not  designed to collect causal information. Additionally, we believe that  knowledge of why an event occurred should not be needed to report  whether a pilot witnessed or experienced a specific event.
section_title: A New Survey Would Require Detailed Planning and Revisiting Sampling Strategies
paragraphs: A new survey similar to NAOMS would require more coherent planning  and sampling methods linked to specific analytic goals. In addition, the  NAOMS survey exhibited some limitations that others might want to avoid.  Sufficient survey methodology literature and documentation on NAOMS’s  memory experiments are available to conduct another survey of its kind  with similarly strong survey development techniques, built on a similarly  strong foundation. The sections that follow suggest some elements of a  new survey like NAOMS.
subsections: section_title: Conduct a Cost-Benefit Analysis
paragraphs: Before undertaking a similar survey, researchers should review  developments in aviation safety and also the costs of and potential for the  NAOMS data to enhance policymakers’ ability to measure trends and  effects on safety interventions. As NAOMS’s application to OMB observed,  managers seek rational and data-driven approaches to aviation safety,  which “requires numbers that quantify the safety risks these investments  are expected to reduce, numbers that reveal trends portending future  safety problems, and still more numbers that measure the effectiveness of  past safety investments.”
NAOMS air carrier data demonstrate that surveys can be used to generate  trend data measuring aspects of aviation safety, and some of the team’s  researchers believe that the data’s utility for monitoring the effect of  policy interventions has already been demonstrated. A survey like NAOMS  could supplement other safety information, but additional analysis must  determine whether NAOMS can be sufficiently useful and cost-effective,  given more recent events and technological developments. For example,  digital flight data could potentially provide monitoring information, but  they are not yet comprehensive or regularly and thoroughly analyzed.  Additionally, many data sources, such as digital measurements of flight  parameters, cannot illuminate behavioral or perceptual information from  operators that might bear on aviation safety. Until such capacity exists, a  survey like NAOMS may nonetheless cost-effectively supplement other  safety information and identify where to look for other sources of safety  information.
A thorough cost-benefit analysis should include the cost of additional  steps to develop the survey, such as further experiments, questionnaire  revisions, and pretesting. Such an analysis should also address the  potential costs and benefits of the survey in light of resources required to  analyze other sources of safety information. For example, the cost of  collecting and analyzing NAOMS-like data may be small relative to the cost  of thoroughly analyzing digital flight data, but, depending on the  questionnaire design, such analysis may not identify causation.
section_title: Capitalize on Experimentation and Testing
paragraphs: A future survey should build on the insights gained from NAOMS’s  extensive developmental research on pilots’ memory organization and  ability to recall events. The survey might undertake additional  experiments and testing to accommodate survey revisions resulting from  stakeholder interests and lessons learned from the NAOMS air carrier pilot  survey. A survey might supplement experiments with additional cognitive  interviews, behavioral coding, and reviews. Researchers should consider  the resources needed for wide-scale testing during the survey’s  development. Whereas research demonstrates the benefits of adapting a  survey’s content to the subject matter and population of interest,  researchers would want to consider the availability of resources and time  to conduct the experiments necessary to reduce respondent burden and  increase accuracy. Additionally, researchers should engage in data  validation efforts beyond establishing face validity when making important  design decisions, such as which recall period to use.
Generally accepted survey practice is to use a field trial to test a  questionnaire that is as similar as possible to the final questionnaire.  Accordingly, a future survey might attempt to incorporate the results of  the experiments, cognitive interviews, and full set of questions into a field  trial questionnaire. A future survey should also run a monitored CATI  pretest on the final version of the questionnaire, to test the automated  programming and ensure that interviewers and respondents appear to  interpret questions correctly.
section_title: Collaborate with Customers in the Survey’s Development
paragraphs: Beyond soliciting and incorporating feedback from aviation safety  stakeholders, staff promoting a new survey like NAOMS should work  directly with the survey’s presumed customers to specify the uses of the  data. While it is not essential that these data inform policy interventions,  policymakers should agree on their potential utility. A customer’s rejection  of the premises of a data collection system—as happened with FAA’s  rejection of the idea that NAOMS would provide a reliable safety  monitoring system—should be resolved before full data collection begins,  and consensus on the survey’s goals and uses should be formally  documented. Otherwise, alternative customers should be identified or the  survey’s design and goals should be revisited. Consulting with potential  customers on the wording and likely use of specific questions would  enhance the utility of the survey’s data. An analysis of the existing NAOMS  data by both scientists and customers’ representatives could help  demonstrate how specific analytic products might directly or indirectly  serve organizational missions.
section_title: Assess Whether Questionnaire Content Facilitates Planned Analyses
paragraphs: In the NAOMS air carrier pilot survey, there is the potential for more than  one crew member on the same aircraft or on separate aircrafts to have  reported the same incident. Proportional allocation or segregated analysis  of different types of crew might help address the potential for multiple  reports of the same event but can be difficult to implement. Nevertheless,  survey designers should consider their analytic goals when designing the  questionnaire—that is, are they looking for per-crew member risk  estimates or system counts? Certain goals may require researchers to  adjust the data, while others may not. Overall, survey designers should be  prepared to compare the sensitivity of their estimates with different  strategies and under different assumptions.
Future efforts to collect safety information from pilots in a survey might  also reconsider the potential effect of sampling pilots who fly more than  one type of aircraft during the recall period or in more than one crew  capacity. The survey designers might want to consider whether NAOMS’s  confidentiality considerations outweigh the potential benefits of allowing  pilots to link reported events to particular aircraft, given the perceived link  between operational size class and risk exposure. To facilitate estimates,  the designers of a future survey should also explore the feasibility of  modifying the questionnaire to allow pilots to identify specific aircraft and  crew capacities associated with each report of a safety event. They would  benefit from establishing an analysis plan in conjunction with the  questionnaire. Doing so would help determine the utility of adding and  deleting questions and would clarify, at the analysis stage, the effect that  doing so would have on data collection.
section_title: Detail Analytical Goals and Strategies in Advance of Fielding
paragraphs: To ensure consensus on the usefulness of the data, a detailed analysis plan  should be developed. The plan should include basic information on likely  estimating the strategies and uses of the data, as well as detailed  information on likely adjustments or weights needed to take account of  questionnaire design and sampling and of the potential uses of the data.  Any adjustments to the analysis plan for operational considerations,  preliminary results, policy changes, or unforeseen circumstances should  be formalized as data collection progresses.
NAOMS was intended to capture precursors to accidents and  nonsignificant risks and to supplement other aviation safety information. It  was expected that rate trends seen in the NAOMS data would point  aviation safety experts toward what to examine in data systems.  Therefore, aviation safety experts and stakeholders would have to conduct  more extensive analysis than was conducted in the NAOMS project to  establish whether rates and trends could be used for this purpose.  Additionally, for a similar survey, analysis would have to establish whether  data generated from different recall periods, interview methods, or  operational size categories were sufficiently similar to allow data to be  combined, and whether making adjustments to sampling strategies or  question wording is necessary to accommodate analytic goals.
The NAOMS survey was intended to provide a better understanding of the  safety performance of the aviation system, and to allow for the  computation of general trends over time, in order to supplement safety  systems. A survey with a different goal—one that was investigative or  intended to understand the causes of events—would seek information  different from those asked for in the NAOMS questions. Depending on the  customers’ intended use of the data, developers of a future survey might  consider writing questions that asked about, for example, the causes of  engine failures or details about air crews’ experience of engine shutdowns.  Whereas questions such as the latter would be consonant with NAOMS’s  goal of describing precursors to safety events, the former would be more  investigative. Developing a detailed analysis plan in conjunction with the  questionnaire would help ensure that the survey included questions  relevant for specific analyses.
section_title: Revisit Sampling Strategy
paragraphs: Given the proportion of out-of-scope cases drawn into NAOMS’s filtered  sample, and the cost of finding and contacting them, the designers of a  future survey should reevaluate the merits of using a database like the  Airmen Registration Database as a sampling frame relative to potential  alternatives, to ensure that the database is still the most cost-effective or  programmatically viable means of identifying the target population.  Other frames, such as industry or union lists, might be considered or  alternative stratification and filtering strategies might be used to identify  air carrier pilots. Sampling strategies must also consider whether the  proliferation of cell phones will require adjusting contact methods to  target a population as mobile as pilots.
Analysis of data such as the NAOMS data might compare different  approaches to calculating trends and exposure rates to see if substantive  conclusions were similar. Analysts might also want to determine how their  estimates relate to the overall NAS. For example, if estimates can address  only crew-based risk exposure, they probably do not characterize the NAS,  although they may provide other important information for aviation safety  monitoring. To the extent that characterizing event levels for the NAS is a  goal, a survey like NAOMS might require a different sampling strategy than  for a survey designed primarily to monitor trends. Sampling records,  including sources used to construct a sample frame and the frame itself,  should be maintained for potential use in estimates and nonresponse bias  analyses.
section_title: Write a Detailed Implementation Plan
paragraphs: A detailed implementation plan would help ensure the continuity of  management and record-keeping for the project and would help ensure  that steps like data validation and bias analyses are carried through on a  schedule. Given the risks and trade-offs inherent in any survey endeavor,  such a plan would also help to ensure that future analysis of the data can  accommodate decisions made in the face of changing conditions or for  practical considerations.
While benchmarking and face validity checks are important aspects of  data validation, they may not be sufficient to confirm the accuracy of pilot  recall or estimate the potential effect of nonresponse bias. Even so,  besides conducting quality checks on the interview process, future survey  developers should undertake formal data validation efforts during data  collection and questionnaire development. Nonresponse bias analyses  should be planned and completed. The survey’s sponsors should allocate  resources to fully benchmark the data.
NAOMS’s confidentiality provisions appear to have been adequate.  Nevertheless, researchers interested in implementing a similar survey  might find it useful to further delineate the kinds of data that might be  released and the techniques that might be used to remove identifiers from  datasets before implementing the survey. In light of other agencies’  mechanisms for releasing individual-level data to screened researchers in  a controlled fashion, survey documentation should also clarify the  conditions under which data could be released to outside researchers, as  appropriate.
While the NAOMS extended survey sample fielding period may have been  necessary to attain a high response rate from a population as mobile as  pilots, future researchers should compare the nature of the answers from  pilots who were contacted with relative ease with the answers from pilots  who it took greater effort to contact. These researchers should also  consider an extended field period’s implications for how quarterly  statistics are generated in light of potential changes to the sampling frame  over time.
There is some merit to NASA’s assertion that the working groups could not  conduct any data validation, without access to the data. In a future survey,  such groups might be constituted earlier, so that data are available for  discussions on data validation. A future effort might use such working  groups in parallel with data collection, thus soliciting and formalizing the  participation of stakeholders. This parallel effort might help the new effort  begin validation as soon as sufficient data are collected. It might also help  circumvent disputes over the potential uses of the survey data.
Finally, researchers pursuing efforts similar to the NAOMS project might  usefully delineate in advance exactly how rates will be calculated, how  potential issues will be clarified, and how the data will be interpreted. A  future survey might benefit from tighter coordination between its  designers and contractors to ensure that public presentations of  preliminary results, when there is still significant debate about the validity  of the results, show only the numbers agreed to by project staff.
section_title: Concluding Observations
paragraphs: As a monitoring tool, NAOMS was intended to point air safety experts  toward trends, to help show FAA and others where to look for causes or  extremely rare safety events in other datasets. As a research and  development project, NAOMS was a successful proof of concept.  However, the data that NASA collected under NAOMS have not been fully  analyzed or validated by project staff or aviation safety stakeholders.  Depending on the research objective, proper analysis of NAOMS data  would require multiple adjustments. Additionally, because of their age,  existing NAOMS data would most likely not be useful as indicators of the  current status of the NAS. “The NAOMS survey could be very useful in sampling flight crew perceptions of safety, and  complementing other databases such as ASRS. The survey data, when properly analyzed,  could be used to call attention to low-risk events that could serve as potential indicators for  further investigation in conjunction with other data sources.”
In this report, we have both described NAOMS’s limitations sufficiently to  enable others to look at redesigning them and suggested ways in which a  newly undertaken project might successfully go forward. The planners and  designers of a new survey might want to supplement it where NAOMS was  self-limiting, by incorporating research into investigatory questions of the  type that interested FAA, or to more specifically detail its monitoring  capacity in conjunction with existing aviation safety systems.  Alternatively, a newly constituted research team might lead operational,  survey, and statistical experts in extensively analyzing existing data to  validate a new survey’s utility for various purposes or to illuminate future  projects of the same type.
section_title: Agency Comments and Our Evaluation
paragraphs: We provided a draft of this report to the National Aeronautics and Space  Administration and to the Department of Transportation for their review.  Transportation had no comments on the draft report. NASA provided  written comments, and appendix II contains a reprint of the agency’s  letter. NASA also provided technical clarifications, which we incorporated  into the report as appropriate.
In response to the draft report’s characterization of NAOMS, NASA  emphasized that NAOMS was a research and development initiative. We  revised the report to more clearly reflect this aspect of NAOMS. NASA also  stated that the draft report inappropriately asserted that NAOMS’s goals  changed over time, and noted that the principal goal of the project was  always to develop a methodology to assess trends or changes over time.  While we recognize that this was a primary goal of the project and have  revised the report to clarify this issue, we believe that the project staff  were not consistent in how they presented NAOMS’s likely capabilities to  other aviation stakeholders over the life of the project. NASA was also  concerned about the draft report’s discussion about maintaining pilot  confidentiality, citing its own research on the risk of pilot disclosure in the  NAOMS data and the inability to determine individuals’ motivation for  trying to identify a specific pilot. We agree with NASA’s concern about  pilot identification and have revised the report to highlight NASA’s  concern; however, we also note that other government agencies have  developed mechanisms for releasing, in a controlled manner, extremely  sensitive raw data with high risk for the identification of individuals to  appropriate researchers.
We also provided a draft of this report to Battelle (NASA’s contractor for  NAOMS) and Jon A. Krosnick, Professor, Stanford University (the survey  methodologist for NAOMS) for their review. Battelle provided no  comments on the draft report. Dr. Krosnick reported that he found the  draft report to be objective and detailed, and that he believed it will  contribute to the public debate on NAOMS. He also provided technical  clarifications, which we incorporated into the report as appropriate.
As agreed with your offices, unless you publicly announce its contents  earlier, we plan no further distribution of this report until 30 days after its  issuance date. At that time, we will send copies of this report to relevant  congressional committees, the Administrator of the National Aeronautics  and Space Administration, the Secretary of the Department of  Transportation, and the Administrator of the Federal Aviation  Administration, and other interested parties. The report also will be  available at no charge on the GAO Web site at http://www.gao.gov.
If you or your staffs have questions concerning this report, please contact  Nancy Kingsbury at (202) 512-2700, kingsburyn@gao.gov, or Gerald  Dillingham at (202) 512-2834, dillinghamg@gao.gov. Contact points for our  Offices of Congressional Relations and Public Affairs are on the last page  of the report. GAO staff who made key contributions to this report are  acknowledged in appendix III.
Nancy R. Kingsbury, Ph.D.  Managing Director, Applied Research and Methods  erald L. Dillingham, Ph.D.
section_title: Appendix I: Technical Issues Relating to NAOMS’s Development and Data
paragraphs: In this appendix, we present in more detail a few topics we discuss in the  report. They are the (1) National Aviation Operations Monitoring Services’  (NAOMS) memory experiments; (2) NAOMs’s cognitive interviews with  pilots; (3) estimating the effect of the sampling frame, filter, and  operational considerations; (4) outlier detection and mitigation; and (5)  allocation strategies.
subsections: section_title: Memory Experiments
paragraphs: The recall and memory experiments for the core safety event section  began with three focus groups conducted in August and September 1998,  consisting of 37 pilots, and one-on-one “autobiography” interviews of 9  pilots. The autobiographies gave the team insight into pilots’ experiences  and how they thought about events, enabling the team to develop potential  event clusters that matched general categories suggested by the pilots’  responses. The focus groups and autobiographies helped in generating  questions about different types of events that would link to the major  hypothesized memory structures—flight phases, causes, and severity—and  eventually a hybrid type that contained causes and flight phases.
The NAOMS team and its subject matter experts then listed 96 events— some based on actual experiences, some purely hypothetical—that  covered different permutations of these events. For example, they  differentiated between minor, moderate, and major problems during  takeoff, cruise, and other phases of flight, involving specific causes and  resulting in specific events. Examples were “major, approach, weather,  spatial deviation” and “minor, landing, people-problem with a conflict or  in-flight encounter.” A sorting experiment used the list derived from this  process. Researchers gave 14 pilots 96 randomly sorted cards, each  containing an individual event, and asked them to sort these cards into  stacks containing events that were similar to one another, and to label the  stacks descriptively. This sorting task further confirmed potential clusters  in the pilots’ memory structures. A quantitative analysis of four competing  hypotheses of organizational schemes (cause, flight phase, combined  cause and flight phase, and severity) showed that the scheme that  contained both causes and flight phases best explained the results of the  sorting experiment.
The project team also assessed the order in which pilots recalled events.  The team transcribed the 96 events onto individual sheets of paper and  randomly sorted them before presenting them to 9 pilots to read. The  pilots then were asked to solve a set of anagrams completely unrelated to  aviation—a “distraction” activity to clear their minds—before recalling  specific events from the list of 96 events. The researchers tape-recorded  what the pilots said, transcribed the responses, and analyzed the resulting  data, using an index called “adjusted ratio of clustering” for each of the  four hypothesized schemes. Data again indicated that a scheme combining  causes and phases of flight best represented pilots’ prevalent memory  structures.
For a final confirmatory test of the best organizational approach to pilots’  memory structures, the project team randomly assigned 36 pilots to 1 of 4  experimental conditions. This test was similar to the recall study, except  that pilots in 3 of the experimental conditions were offered cues to prompt  event recall (cause, phase, or a combination of the two). The cues that  combined cause and phase appeared to optimize the number of specific  events that a pilot could recall.
A memorandum summarizing these results added a final caveat on  question order: that is, events were to be ordered from the weakest in  memory to the strongest in memory. This ordering would accord with  literature that showed that strong memories can obscure lesser ones in the  same memory cluster. The memorandum’s author recommended further  research with pilots to develop a ranking of weak to strong memories. It  does not appear that formal analysis was conducted, although it is likely  that some NAOMS researchers tapped into their own flying and other  aviation experience to help sort events on the final questionnaire.
section_title: Cognitive Interviews
paragraphs: For the full air carrier pilot survey, researchers interviewed four Aviation  Safety Reporting System (ASRS) analysts, all of retired pilots, plus seven  active pilots recruited from personal friends of NAOMS staff. At least six  of the seven active pilots were air carrier pilots who would have been  within NAOMS’s target population.
The questionnaire was revised between the three separate sets of cognitive  interviews, but not between participants within a set of interviews—the  four ASRS analysts, the six air carrier pilots, and the 7th pilot. The  revisions included changes the survey methodologist recommended to  more appropriately match the memory structure that the earlier  experiments had revealed, as well as changes to accommodate issues  raised in the cognitive interviews. We do not have evidence to suggest  whether the questionnaire’s final version was cognitively tested before the  survey’s implementation. Interviewers and Battelle Memorial Institute  (Battelle) managers did conduct a series of interviews to test the flow of  the computer-assisted telephone interview (CATI) programming before  the survey was implemented.
section_title: Estimating the Effect of the Sampling Frame, Filter, and Operational Considerations
paragraphs: The decisions that decreased the likelihood of identifying the NAOMS  survey respondents made it necessary for analysts to adjust their  estimates. In making adjustments, analysts generally look to their  analytical goals and to the likely effect of an adjustment on the substantive  interpretation of an estimate compared with an alternative. The analysts  also try to explore whether adjustments made to address specific  problems affect adjustments to address other issues. For example, a series  of adjustments to address different features or limitations of the data may  render the interpretation of estimates too complicated for practical use.  Changes in external datasets used for benchmarking or in creating  projections may affect the interpretability of the data over time. In the  case of the NAOMS data, sampling, design, and implementation decisions  complicate straightforward estimates for either system counts or rates.
For a full analysis to account for issues related to questionnaire design,  sampling, and implementation, the NAOMS air carrier data would require  multiple adjustments and imputation. Additional analyses would be  required to determine the nature and effect of these adjustments. Before  the project’s end, NAOMS researchers analyzed potential biases that they  believed resulted from the filter used to identify air carrier pilots from the  sampling frame. These analyses are critical for determining the  appropriate uses of the data. We believe that the first priority for further  analysis is to estimate the effect of the sampling frame. That is, however  appropriate NAOMS’s use of the publicly available Airmen Registration  Database may have been for cost and programmatic considerations, it has  not yet been established whether the frame sufficiently represented air  carrier pilots in general, especially in light of pilots’ ability to opt out of the  registry.
Potential analytic approaches to assessment include but are not limited to  the following:    Comparing pilots’ reported airline fleet characteristics in the survey  with outside data on the size of air carrier fleets. NAOMS project staff  added a question on airline fleet size to the survey expressly to be able to  gauge whether the pilots in the Airmen Registration Database flew in fleets  similar to the air carrier fleet distribution as a whole. While this analysis  might provide compelling information about how representative the frame  was, it is insufficient to demonstrate that the frame fully represented air  carrier pilots of interest or air carrier pilots covered by the full frame. For  example, it is conceivable that the distribution of pilots’ airline fleet  characteristics correspond between NAOMS data and data derived from  other sources, but that the distribution of pilot characteristics within each  fleet size was systematically biased toward more experienced pilots who  were better able to foresee and avoid safety-related events.
Comparing pilot characteristics from the publicly available frame or the  sample (as a random subset of the frame) with the full database that the  Federal Aviation Administration (FAA) maintained. Ideally, the  comparison would have been made with files used for survey fielding.  However, Battelle has reported that it does not have enough data to make  such a comparison. A NAOMS team member suggested that for an  alternative, one could compare the full FAA database with the publicly  available registry on a range of characteristics both relevant and external  to NAOMS’s concerns. Without knowing whether the nature of the opt-out  registry had changed over time, this analysis would help determine  whether pilot characteristics in the public frame can be generalized to  those in the full frame. However, because neither database contains  information on pilots’ employment or union membership, this analysis  would be insufficient to determine whether the frame used for NAOMS  data collection was systematically biased to include or exclude pilots from  certain airlines or unions. Thus, this approach would complement, not  replace, the analysis comparing fleet characteristics discussed in the  previous bullet.
Conducting something like a nonresponse bias assessment. Analysts  would take random samples of pilots within the filtered frame as it would  be constructed from the publicly available database and from the full FAA- maintained database and would use a survey to compare pilot  characteristics for these two samples. Ideally, this would have been done  during the survey field trials; however, in the absence of compelling  evidence that the nature of the two databases had changed over time, the  comparison could still provide insight on whether pilots in the opt-out  frame were sufficiently similar to those in the full database to treat the  opt-out frame as representative of the population. Depending on its design,  a study such as this would allow analysts to focus on characteristics that  were most relevant to NAOMS, such as career flying hours or experiences  of safety events, and would also provide a means of gauging potential bias  in terms of employers, union membership, and other factors that are not  expressly collected in the certificate database.
In any case, analysts of NAOMS data must pursue additional research to  determine the existence and nature of potential biases from using the  public database rather than the full database, and determine whether and  which analytic strategies will ensure that the results adequately  represented safety events in the population of interest.
In addition to adjustments for sampling considerations, other analyses  may be useful in generating estimates and necessary adjustments. For  example, to mitigate the effect of coverage bias in systemwide event count  estimates, the NAOMS team advocated using Bureau of Transportation  Statistics data related to operational size categories, carrier size, flight  hours, and flight legs as benchmarks for weighting these data. The  feasibility of using exogenous information to weight NAOMS data depends  heavily on achieving a consensus on the appropriate and inappropriate  uses of the survey regarding measuring risk exposure and safety events in  the national airspace system (NAS).
Battelle recommended statistical modeling—in particular, generalized  linear modeling—to develop “more refined rate estimates.” Generalized  linear models would have allowed estimates of safety event rates, while  controlling for the independent effect of factors such as season and  operational aircraft size. Battelle conducted preliminary modeling with  generalized linear regression models on grouped sets of data. The utility of  such models is contingent on the goals of the analysis and the nature of  bias or patterns of missing data; adjusting for independent factors may not  be appropriate when generating rate estimates to project to the  population. One Battelle statistician noted that NAOMS data lacked  important explanatory factors, and that statistical models could suffer  from omitted variable bias (which is unrelated to whether these data can  be projected to the population of interest). This criticism did not account  for the fact that NAOMS’s data were not designed to be used for an  investigative process or to establish causation.
Estimates from NAOMS are further complicated by the need to distinguish  between risk based on time exposure and risk related to the number of  takeoffs and landings. Analysts using NAOMS data might want to compare  various approaches to calculating trends and exposure rates to see if  different analyses result in similar substantive conclusions. They should  also clarify whether and how estimates relate to the overall system—for  example, if they can address only crew-based risk exposure, one might ask  whether this is sufficient for characterizing the NAS.
section_title: Outlier Detection and Mitigation
paragraphs: Outliers can greatly influence the interpretation of statistical analyses.  Outlier detection and cleaning, which should consider both statistical and  operational concerns, require help from subject matter experts who can  identify whether a given data point seems “reasonable” in context.  Researchers may also consider whether data follow statistical  distributions, such as binomial or Poisson distributions, in deciding how to  identify or exclude outliers. Additionally, researchers should consider  whether the unit of analysis (whether counts or rates) leads to identifying  different cases of outliers and the effect of various methods of outlier  detection and cleaning on the substantive interpretation of the analysis.
Causes of outliers can be respondents’ mishearing or misinterpreting a  question or deciding not to respond truthfully. Outliers may also reflect  accurate data that do not correspond with the preponderance of cases.  For example, one Battelle researcher cited the “cowboy theory” of aviation  safety—the notion that the vast majority of accidents are caused by a  small proportion of pilots. Battelle also suggested that some pilots might  report events that they had not experienced in order to deliver a message  about safety.
Survey research data collected by CATI methods are also subject to  several types of outliers. An interviewer may mistype a response—for  example, entering 3 as 33. CATI systems often use range checks to prevent  such errors: that is, if what is typed exceeds a numerical threshold, the  interviewer is prompted to ask the question again or to key the data again.  Few hard range checks were incorporated into the NAOMS CATI program,  because NASA had instructed the contractor not to question the veracity  of pilots’ responses by having interviewers re-ask questions if a response  seemed unusual. The lack of range checks makes it more difficult to  distinguish between outlying answers that were mistyped and those that  represented accurate respondent answers. The use of free-text fields to  record aircraft type may also have complicated the identification of  unreasonable answers for air carrier pilots.
For most questions, the contractor developed an outlier cleaning method  that was thought to be both appropriate and objective. This method was  used to identify and remove cases of “doubtful quality” (such as whether  the ratio of flight hours to flight legs was unreasonable or whether a pilot  had “unreasonable” values on multiple questions), cases lacking  information in the questionnaire’s fields on flight activity, and additional  outliers flagged as “not applicable.” Although the method provided a  consistent means of approaching outliers for each question, it did not  account for whether reported values made sense in an operational  context. Furthermore, the method was developed only midway through  data collection. Had the method been developed farther along, more data  might have helped clarify whether a distribution-based approach to outlier  detection would have been appropriate. To more thoroughly consider  statistical and operational concerns, further strategies for data cleaning  and outlier detection would benefit from using the full data.
section_title: Allocation Strategies
paragraphs: The NAOMS survey has the potential to collect multiple reports of safety  events witnessed by more than one crew member or involving multiple  aircraft. Several NAOMS researchers believe that the effect of this issue  has been overstated, particularly in light of potential analytical strategies  to remedy this problem. Additionally, such concerns do not apply to  analyses that determine per-crew member risk exposure (as compared  with systemwide projections of event counts), if each individual crew  member had an equal chance of being selected.
Strategies that researchers have suggested for addressing the potential for  multiple reports of the same event include proportionally allocating events  by the likely number of crew members on each aircraft. However, because  the number of crew members varies by aircraft size and flight—for  example, long international flights require relief crews—this strategy is  complicated by the inability to determine for certain which aircraft was  involved in a specific incident when a pilot flew more than one aircraft  during the recall period.
An alternative strategy would be to calculate events reported by pilots  who flew as captains separately from those events reported by other  pilots—that is, first officers, flight engineers, and relief pilots. However,  this approach might also be complicated by the possibility that pilots flew  in more than one capacity over the recall period and the questionnaire  does not allow pilots to identify whether they were the captain when  experiencing a reported safety event. Furthermore, to the extent that  sampling techniques resulted in bias related to the likelihood of flying in a  given capacity—that is, the so-called “left-seat bias” that resulted in  disproportionate sampling of captains thought to have resulted from the  sample filter—segregated analysis of different crew members would  require adjustments to project event counts systemwide.
The inability to link reported safety events for pilots who flew more than  one aircraft type to a specific aircraft (and, by implication, to a crew size)  or day requires developing allocation strategies for other aspects of the  data. Before settling on the nonproportional allocation strategies that we  describe in this report, Battelle explored alternatives for allocating aircraft  among operational size categories and seasons in its preliminary analyses  of NAOMS data. For both size category and season, Battelle first  attempted to allocate reported safety events and hours flown  proportionally across the number of days in a given season or according to  the percentage flown per aircraft. Both allocations proved unsatisfactory  as it became administratively infeasible for the NAOMS team to maintain  either system as data collection continued. Additionally, the allocations  resulted in fractional degrees of freedom, in that reports from pilots that  were split across seasons or aircraft were treated as less than a full case.  Similarly, treating proportionally allocated safety events entails theoretical  difficulties—for example, was it legitimate when calculating rates to count  one-half or one-third of a bird strike?
While proportional allocation or segregated analysis of different types of  crews may help to account for potential reports of the same event, these  strategies may be difficult to implement because pilots could have flown  more than one aircraft type or in multiple crew capacities during the recall  period and because of seasonal patterns in the data. As with other weights  and adjustments, researchers need to consider their analytical goals—for  example, whether they are looking for per-crew member risk estimates or  system counts—and should be prepared to compare the sensitivity of their  estimates with different strategies and different assumptions. Analysts  should also assess whether and how the necessity of multiple adjustments  and allocations limits the utility of the data for characterizing trends in air  carrier aviation safety.
section_title: Appendix II: Comments from the National Aeronautics and Space Administration
section_title: Appendix III: GAO Contacts and Staff Acknowledgments
subsections: section_title: GAO Contacts
section_title: Staff Acknowledgments
paragraphs: In addition to the persons named above, H. Brandon Haller, Assistant  Director; Teresa Spisak, Assistant Director; Carl Barden; Ron LaDueLake;  Maureen Luna-Long; Grant Mallie; Erica Miles; Charlotte Moore; Anna  Maria Ortiz; Dae Park; Penny Pickett; Mark Ramage; Carl Ramirez; Mark  Ryan; and Richard Scott made key contributions to this report.
section_title: Bibliography
paragraphs: Many publicly available documents on the National Aviation Operations  Monitoring Service (NAOMS) are at the National Aeronautics and Space  Administration’s (NASA) Web site dedicated to the NAOMS project  (www.nasa.gov/news/reports/NAOMS.html, last accessed Mar. 1, 2009) or  at other NASA Web sites where materials on NAOMS and the Aviation  Safety and Security Program are archived and searchable. The Committee  on Science and Technology of the House of Representatives maintains  additional information related to its October 31, 2007, hearing on NAOMS  through its Web site at http://science.house.gov/publications/ (last  accessed Mar. 1, 2009).
Battelle Memorial Institute. NAOMS Reference Report: Concepts, Methods,  and Development Roadmap. Prepared for the National Aeronautics and  Space Administration Ames Research Center. November 30, 2007.
Connell, Linda. NAOMS Workshop: National Aviation Operations  Monitoring Service (NAOMS). Washington, D.C.: National Aeronautics  and Space Administration, March 1, 2000.
Connell, Linda. Workshop on the Concept of the National Aviation  Operational Monitoring Service (NAOMS). Alexandria, Va.: National  Aeronautics and Space Administration, May 11, 1999.
Connors, Mary, and Linda Connell. “The National Aviation Operations  Monitoring Service: A Project Overview of Background, Approach,  Development and Current Status.” Presentation to the NAOMS Working  Group 1. Seattle, Wash.: National Aeronautics and Space Administration,  December 18, 2003.
Dodd, Robert S. Statement on the National Aviation Operations Monitoring  Service, October 28, 2007. Statement on the National Aviation Operations  Monitoring Service. Statement before the Committee on Science and  Technology, House of Representatives, U.S. Congress. Washington, D.C.:  October 31, 2007.
Griffin, Michael D., Administrator, National Aeronautics and Space  Administration. Letter to National Aeronautics and Space Administration  employees on NAOMS. Washington, D.C.: January 14, 2008.
Griffin, Michael D., Administrator, National Aeronautics and Space  Administration. Statement on the National Aviation Operations Monitoring  Service. Statement before the Committee on Science and Technology,  House of Representatives, U.S. Congress. Washington, D.C.: October 31,  2007.
Griffin, Michael, Administrator, and Bryan D. O’Connor, Chief, Safety and  Mission Assurance, National Aeronautics and Space Administration.  “Release of Aviation Safety Data.” Media briefing moderated by J. D.  Harrington, National Aeronautics and Space Administration Office of  Public Affairs. Washington, D.C.: December 31, 2007.
Krosnick, Jon A. Statement on the National Aviation Operations  Monitoring Service, October 30, 2007. Statement before the Committee on  Science and Technology, House of Representatives, U.S. Congress.  Washington, D.C.: October 31, 2007.
McVenes, Terry, Executive Air Safety Chairman, ALPA International.  Statement on the National Aviation Operations Monitoring Service.  Statement before the Committee on Science and Technology, House of  Representatives, U.S. Congress. Washington, D.C.: October 31, 2007.
Miller, Brad, Chairman, Subcommittee on Investigations and Oversight,  Committee on Science and Technology, House of Representatives, U.S.  Congress. Letter to Robert Sturgell, Acting Administrator, Federal Aviation  Administration. Washington, D.C.: July 23, 2008.
National Aeronautics and Space Administration. National Aviation  Operations Monitoring Service Application for OMB Clearance. Moffett  Field, Calif.: Ames Research Center, June 12, 2000.
National Aeronautics and Space Administration. “National Aviation  Operational Monitoring Service (NAOMS): Development and Proof of  Concept.” Presentation to the Aviation Safety Reporting System Advisory  Subcommittee. Washington, D.C.: November 13, 1998.
National Aeronautics and Space Administration. “Creation of a National  Aviation Operational Monitoring Service (NAOMS): Proposed Phase One  Effort.” Presentation to the Flight Safety Foundation Icarus Committee  Working Group on Flight Operational Risk Assessment. Washington, D.C.:  March 5, 1998.
National Aeronautics and Space Administration, Office of Safety and  Mission Assurance. “Final Report of the National Aeronautics and Space  Administration (NASA) National Aviation Operations Monitoring Service  (NAOMS) Information Release Advisory Panel (2008).” Memorandum to  the Associate Administrator, National Aeronautics and Space  Administration. Washington, D.C.: May 12, 2008.
National Aeronautics and Space Administration, Office of Inspector  General, Assistant General for Auditing. “Final Memorandum on the  Review of the National Aviation Operations Monitoring Service (Report  No. IG-08-014; Assignment No. S-08-004-00),” to the Associate  Administrator for Aeronautics Research, National Aeronautics and Space  Administration. Washington, D.C.: March 31, 2008.
Statler, Irving C. Aviation Safety and Security Program (AvSSP): 2.1  Aviation System Monitoring and Modeling (ASMM) Sub-Project Plan,  Version 4.0. Washington, D.C.: National Aeronautics and Space  Administration, February 2004.
Statler, Irving C., ed. The Aviation System Monitoring and Modeling  (ASMM) Project: A Documentation of Its History and Accomplishments  1999–2005. Washington, D.C.: National Aeronautics and Space  Administration, June 2007.
White House Commission on Aviation Safety and Security. Final Report to  President Clinton. Washington, D.C.: The White House, February 12, 1997.