“An airplane that spends an hour on the ground between flights might fly five trips a day,” he explains. “Cut the turnaround time to 40 minutes, and maybe that same plane can complete six or seven flights a day.” More flights mean more paying passengers, and ultimately, more revenue.
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Convinced that there was a statistical solution to the problem, Lindemann approached Arizona State University’s industrial engineering department. “We have a great university in our backyard, and hoped they could help,”
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Professor René Villalobos and graduate student Menkes van den Briel began reviewing boarding systems used by other airlines. “The conventional wisdom was that boarding from back to front was most effective,” says van den Briel. The engineers looked at an inside-out strategy that boards planes from window to aisle, and also examined a 2002 simulation study that claimed calling passengers individually by seat number was the fastest way to load an aircraft.

The two then developed a mathematical formula that measured the number of times passengers were likely to get in each other’s way during boarding. “We knew that boarding time was negatively impacted by passengers interfering with one another,” explains van den Briel. “So we built a model to calculate these incidents.”

Villalobos and van den Briel looked at interference resulting from passengers obstructing the aisle, as well as that caused by seated passengers blocking a window or middle seat. They applied the equation to eight different boarding scenarios, looking at both front-to-back and outside-in systems.
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Villalobos and van den Briel presented America West with a boarding approach called the reverse pyramid that calls for simultaneously loading an aircraft from back to front and outside in. Window and middle passengers near the back of the plane board first; those with aisle seats near the front are called last. “Our research showed that this method created the fewest incidents of interference between passengers,” Villalobos explains, “and was therefore the fastest.”