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Jana Price, Ph.D.

Jana Price, Ph.D. Statistical End Play Data Study. Estimating Reliability of The On-Wing End Play Measure. Reliability: the ability of the on-wing end play measurement to yield repeatable results Measures taken on consecutive occasions were correlated

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Jana Price, Ph.D.

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  1. Jana Price, Ph.D. Statistical End Play Data Study

  2. Estimating Reliability of The On-Wing End Play Measure • Reliability: the ability of the on-wing end play measurement to yield repeatable results • Measures taken on consecutive occasions were correlated • The analysis data consisted of 852 paired measures (Time 1 and Time 2)

  3. Measures of Reliability • Correlation coefficients (r) range from –1.0 to 1.0 • An r value near 1.0 would suggest high measurement reliability • Lower r values indicate less measurement reliability

  4. Plot of Raw End Play Data at Time 1 and Time 2 r = 0.553

  5. Time 2 Smaller than Time 1 Time 2 Equal to or Larger than Time 1 End Play Differences Between Time 1 and Time 2

  6. Estimating Validity of The On-Wing End Play Measure • 157 jackscrew assemblies were returned to Integrated Aerospace (IA) • IA performs a “bench-check” • Measures of on-wing end play and bench-checks were available for 63 jackscrew assemblies • NTSB analysis correlated on-wing and bench check end play measures

  7. On-Wing Less than Bench Check On-Wing Equal to or Greater than Bench Check Differences Between On-Wing and Bench-Check End Play r = 0.442

  8. Conclusions • Repeated on-wing measures show low reliability • Reliability is a necessary condition for an accurate measure • Validity analysis using on-wing and bench-check measures showed low validity • Based on these conclusions, NTSB recommended changes to measurement procedures

  9. Recommendation A-01-042 Revise the end play check procedure … to minimize the probability of measurement error and conduct a study to empirically validate the revised procedure against an appropriate physical standard of actual acme screw and acme nut wear. This study should also establish that the procedure produces a measurement that is reliable when conducted on-wing

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