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According to U.S. Bureau of Transportation Statistics, airlines collected over $2.2 billion in cancellation and change fees in the first three quarters of 2014 compared to $2.1 billion in the same time period of 2013. That is some serious cash, and they’re making more each year."
"The Department of Transportation requires that all airlines either hold a reservation for 24 hours without requiring payment or refund a paid ticket, also within 24 hours, even if the ticket is non-refundable. To invoke the 24-hour rule, you must purchase the ticket seven days before the flight." 
