Why do airlines overbook flights? Here's one answer.

Do you know why American Airlines overbooks coach? Rendering: American Airlines. 

Do you know why American Airlines overbooks coach? Rendering: American Airlines. 

Many of you fly a lot, and you're probably savvy about why airlines overbook flights. 

But in an employee newsletter, American Airlines recently published a short Q & A with Don Casey, the carrier's senior vice president for revenue management. 

I thought you might find his answer about overbooking interesting. He is what he said:

On any given flight we know it’s likely that at least a few customers won’t show up. Some customers might have refundable tickets, or have same-day standby privileges so they switch to other flights. Revenue Management has a model that predicts the right amount of seats to oversell, but in the end we are playing the probabilities and some oversales are inevitable. So even though vouchers aren’t cheap, they cost less than the sales we would give up if we didn’t oversell a little bit. Our denied boarding rates are lower than some of our network peers

As for denied boarding rates, here's how various U.S. airlines compared in 2015, according to U.S. Department of Transportation data. The DOT says it does not include inbound international flights in its tally.