Question: Jet Engine Visual Inspection. The data in Table are representative of counts of nonconformances observed at final assembly at an aircraft engine company. Suppose that one final assembly is inspected per day.
(a) Is this a variables data problem or is it an attributes data problem? Explain.
(b) In the context of the problem, what is a "subgroup"?
(c) What probability distribution is a likely model for counts of non-conformances on these engines? Defend your answer.
(d) Find an estimated mean number of visually identified non-conformances and the corresponding estimated standard deviation.
(e) Find appropriate upper and lower control limits and center line to apply to the counts. Make the corresponding control chart for these data. Does it appear that the process was stable over the period of the study? Why or why not? Identify any out-of-control points. Apply Nelson's rules.
(f) Suppose two inspectors were involved in the data collection. Briefly discuss what must be true (in terms of data collection protocol) to assure that the chart and analysis in (e) are credible.
