Statistical quality control, airline operations.
Air Gascogne operates daily round-trip flights on the Toulouse-Stockholm route using a fleet of three 747s, the Eclair des Cévennes, the Eclair des Vosges and the Eclair des Alpilles. The budgeted quantity of fuel for each round-trip flight is the mean (average) fuel usage. Over the last 12 months, the average fuel usage per round-trip is 1000 litre-units with a standard deviation of 100 litre-units. A litre-unit is 1000 litres.
Gervaise Plassans, the operations manager of Air Gascogne, uses a statistical quality control (SQC) approach in deciding whether to investigate fuel usage per round-trip flight. She inves- tigates those flights with fuel usage greater than two standard deviations from the mean.
In October, Plassans receives the following report for round-trip fuel usage by the three planes operating on the Toulouse-Stockholm route:
|
Flight
|
Eclair des Cévennes (litre-units)
|
Eclair des Vosges (litre-units)
|
Eclair des Alpilles (litre-units)
|
|
1
|
1040
|
1030
|
970
|
|
2
|
940
|
940
|
1040
|
|
3
|
970
|
960
|
1110
|
|
4
|
1010
|
1070
|
1040
|
|
5
|
1050
|
920
|
1220
|
|
6
|
1070
|
1130
|
1180
|
|
7
|
1110
|
990
|
1260
|
|
8
|
1120
|
1060
|
1140
|
|
9
|
1150
|
1010
|
1170
|
|
10
|
1190
|
930
|
1230
|
Required
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 them?
3. Some managers propose that Air Gascogne present its SQC charts in monetary terms rather than in physical quantity terms (litre-units). What are the advantages and disad- vantages of using euro fuel costs rather than litre-units in the SQC charts.