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An Assessment of NASA's National Aviation Operations Monitoring Service (2009) / Chapter Skim
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4 Assessment of NAOMS Sampling Design
Pages 16-22

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From page 16...
... All other pilots were eligible for the GA survey. Budgetary and statistical considerations led the NAOMS team to set a goal of 8,000 completed AC survey questionnaires each year.4 The criteria outlined above resulted in a pool of 52,570 pilots for the AC survey.5 The NAOMS team further narrowed the sample pool by eliminating any pilot who could not be linked to a telephone number.
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From page 17...
... Department of Transportation specifically excludes Part 135 operations and considers Part 135 scheduled operations to be a segment of aviation separate from both general aviation and also from Part 135 on-demand operations.14 The GA survey did not collect the information that would have enabled events from these disparate segments to be disaggregated. The ideal sampling frame for this population would be the list of all flight legs that occurred in the appropriate flight regimes, that is, Part 121 flights in the AC survey and Part 91 and Part 135 (given the NAOMS definition of general aviation)
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From page 18...
... In 2008, coverage of pilots without an FE certificate (the closest available approximation to the GA sampling frame) was 96 percent.17 Finding: If the event rates for pilots who opted out of the public Airmen Certification Database differed considerably from those who did not, the high opt-out rates would have resulted in substantial biases in the AC survey.
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From page 19...
... The NAOMS team deemed that this screening would be too costly, so it decided instead to filter the ACD for pilots with certifications indicative of pilots who fly for air carriers. Specifically, the AC sampling frame was limited to U.S.-based pilots who had an ATP certificate, multi-engine rating, and an FE certificate.
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From page 20...
... In summary, the NAOMS team faced substantial challenges in developing and implementing sampling designs for the AC and GA surveys. As with most real applications, the team had to make compromises in the final design -- most notably in the development of the sampling frames.
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From page 21...
... However, because the decision to cooperate with this type of survey might be influenced by recently experienced safetyrelated events, data comparing respondents with nonrespondents would be particularly valuable for assessing the potential bias due to nonresponse. Taking into account both failure to locate and noncompletion, the estimated overall response rates were 69 percent20 and 50 percent, respectively, for the AC and GA surveys.
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From page 22...
... considerable rounding effects in reported numbers of hours and flight legs flown (see Figure 7.1 in Chapter 7)
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Key Terms

  • sampling frame
  • recall period
  • flight legs
  • air carrier
  • naoms survey

  • aviation operations
  • national aviation
  • professionally trained
  • operations monitoring
  • monitoring service

  • trained interviewers
  • transportation statistics
  • federal aviation
  • airline transport
  • simple random

  • random sample
  • transport pilot
  • target population
  • naoms study
  • study team

  • team decided
  • flight engineer
  • aviation regulations
  • airmen certification
  • aircraft type

  • event rates
  • response rates
  • sampling flight
  • naoms project
  • unequal sampling


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