Statistical quality control, airline operations. Jetrans Airlines operates daily round-trip flights on the London—Los Angeles route using a fleet of three 747s: the Spirit of Atlanta, the Spirit of Boston, and the Spirit of Sacramento. The budgeted quantity of fuel for each round-trip flight is the 12-month mean (average) round-trip fuel consumption of 200 gallon-units, with a standard deviation of 20 gallon-units. A gallon-unit is 1,000 gallons. Using a statistical quality control (SQC) approach, Shirley Watson, the Jetrans operations manager, investigates any round-trip with fuel consumption that is greater than two standard deviations from the mean. In October, Watson receives the following report for round-trip fuel consumption for the three planes on the London—Los Angeles route:

1. Using the ±2σ rule, what variance-investigation decisions would be made?

2. Present SQC charts for round-trip fuel usage for each of the three 747s in October. What inferences can you draw from the charts?

3. Some managers propose that Jetrans Airlines present its SOC charts in monetary terms rather than in physical-quantity terms (gallon-units). What are the advantages and disadvantages of using monetary fuel costs rather than gallon-units in the SOC charts?

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Spirit of Spirit of Spirit of Atlanta Boston Sacramento Flight (gallons-units) (gallons-units) (gallons-units) 208 206 194 187 188 208 194 192 221 4 202 214 208 211 184 242 215 226 234 216 198 249 218 212 227 221 202 232 232 10 186 244 3.