A US airline is concerned about its flights tardiness. The attached spreadsheet displays tardiness data for a sample of 200 days, with 10 flights per day. The numbers corresponds to the flight tardiness (actual arrival time minus scheduled arrival time) in hours. Use the first 1000 observations to answer questions a) through d) below:
a) What is the mean tardiness for the given data? What is the standard deviation (hint: use the function stdev.s in Excel)? What is you assessment of the airline performance in terms of this tardiness measure?
b) Draw a histogram of the flight tardiness for the first 1000 observations (Hint: Use the histogram feature under data analysis in Excel. You may also use other software such as Minitab). Does it resemble the shape of any familiar distribution?
c) The airline wishes to use the data to build a control chart. It considers grouping the data in samples of size 1, 5 or 10. What sample size would you use? Draw histograms to justify your answer.
d) Using the sample size that you selected in e) what are the upper and lower control limits one should use for the control chart?
e) Draw the corresponding control chart using the data from all 200 days. Is the process in control? What do you observe? If there are problems, when do they occur? What are some plausible causes for these problems?
f) How would you improve the tardiness performance of this US airline?