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

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 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 Equal to or Greater than Bench Check On-Wing Less 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 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

10. 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