Between February 1998 and March 2005, NASA conducted a study called National Aeronautics Operational Monitoring System, also known as NAOMS. NAOMS is a survey-based data collection system designed to collect aviation safety data from general aviation and air carrier pilots. NAOMS was designed to quantify aviation safety events and other safety-relevant phenomena. Because incidents posing a threat to aviation safety are relatively rare events, useful analysis requires the acquisition of a large, statistically meaningful database that is representative of the system. These data can be used to identify system-wide trends and establish performance measures with emphasis on tracking the effects of safety interventions (new procedures, technologies, and training) on national aviation safety levels. The NAOMS project selected a contractor to develop a survey methodology to acquire such data. It was recognized that the type of data, which was sought, information on incidents, infractions, and mistakes potentially affecting aviation safety, carries with it the potential for significant risk for the person reporting such information. Prior to interviewing pilots for the NAOMS survey, NASA promised that, those pilots who were willing to participate in the survey could be assured that their identity would be protected. The survey-based project team offered anonymity to those taking part in the survey, and one of the contractor's responsibilities was to anonymize the dataset. Data collection using the methodology began in April 2001 and ended in December 2004, during which time the project team conducted approximately 24,000 surveys of commercial airline pilots and approximately 5,000 general aviation pilots. Research conducted in the NAOMS project, including the survey methodology, has not been peer-reviewed and should not be viewed or considered as having been validated.