Delta Air Lines had 1,238 involuntarily bumped passengers in 2016, a rate of 0.1 per 10,000 passengers. That was the second-best rate among U.S. airlines.
Dallas-based Southwest Airlines, the second-largest carrier at Hartsfield-Jackson, had 14,979 involuntarily bumped passengers last year, a rate of 0.99 percent per 10,000 passengers -- the second-worst rate among U.S. airlines.
Effective in 2011, airline travelers involuntarily bumped from a flight were eligible for double the amount they were previously. The compensation passengers are eligible for is now up to $1,350, depending on the value of their ticket and the length of time they have to wait for another flight.
Atlanta-based Delta was fined for violating rules for compensating involuntarily bumped passengers in 2012.
Getting involuntarily bumped from a flight is very rare. Fewer than one passenger in 10,000 on the largest U.S. airlines is affected on average, according to the U.S. Bureau of Transportation Statistics.
But when it does happen, "It can be really devastating, " said Kate Hanni, executive director of FlyersRights.org. Travelers going on their honeymoons or headed to funerals may come to the airport to find out they don't have a seat, Hanni said. "People believe they have a seat when they buy a seat. They have no reason to believe otherwise, " she said.
Bumping is, in part, due to airlines' practice of overbooking flights to make up for passengers who don't show up.
When seats go out empty, "Over time, it's a significant amount of revenue for an airline, " said Jeff Houston, Southwest Airlines director of revenue management. So airlines generally look at how many no-shows a flight historically generates and overbook slightly.
"Given that the costs of a flight are considerable, particularly with what we're seeing with high fuel prices these days, being able to cover these costs helps us continue to operate, " said Delta Air Lines spokesman Trebor Banstetter.
Involuntary bumping --- or denied boarding, as it is called in airline lingo --- is different from volunteering to take a later flight in exchange for vouchers or similar compensation from the airline. Involuntary denied boarding typically comes after the airline has exhausted its list of volunteers and still has too many passengers to fit on the plane.
Delta credits its relatively low involuntary bumping rate in part to a system it started in 2010 which involves taking bids from passengers checking in online or at an airport kiosk who are willing to volunteer to take a later flight.
In 2016, for example, Delta had the most voluntary denied boardings of any U.S. airline -- 129,825 passengers who volunteered to be bumped.
By accumulating more data on flights over the years, "We get better and better at doing this over time, " Banstetter said. He said Delta is also more aggressive in contacting passengers in advance when their flight is switched to a smaller plane and they must be rebooked to different flights.
Southwest touts its lack of change fees in its advertising, but that also contributes to a higher rate of bumped passengers because the policy produces a slightly higher no-show factor, according to Houston.
Houston said Southwest's philosophy is that charging change fees is a larger negative to customers than a higher overbooking rate.
Southwest, a low-cost carrier battling higher costs, is seeking ways to increase revenue, so it has been trying to fill planes more than before, leading to more bumped passengers.
And Southwest's attempts to gain more business travelers has also added more uncertainty, because business travelers are the most likely to miss a flight and take another one when meeting plans change. They are also more likely to buy higher-priced refundable fares with more flexibility.
"It's just a lot harder to find someplace to put somebody now and as a result, you have to manage the oversales a bit more conservatively, " Houston said.
The 2011 rule doubled the amount of money passengers are eligible for if they are involuntarily bumped from an oversold flight.
Bumped passengers are entitled to cash compensation equal to double the one-way value of their tickets, up to $675, if the airline was able to get them to their destination within a short period of time (within one to two hours of their originally scheduled arrival time for domestic flights and one to four hours for international flights).
If they were delayed for a lengthy period of time (more than two hours after their originally scheduled arrival time for domestic flights and four hours for international flights), they are entitled to four times the value of the one-way price of their tickets, up to $1,350.
Inflation adjustments are made to the compensation limits every two years.
Source: U.S. Department of Transportation
From the AJC on January 13, 2011 when Delta launched its system to take bids for bumping:
Delta takes bids for bumps
How much would it take to get you to give up your seat on an overbooked airline flight?
Delta Air Lines is telling customers to name their price --- in some cases before they even leave for the airport.
Delta, like other airlines, has long had a system of asking for volunteers to be bumped to a later flight in exchange for vouchers toward future travel. Some passengers make a sport out of volunteering and thrive off free flights they collect.
Now, Delta is taking the system one step further. It has turned the voluntary bumping system into an auction that starts online with travelers' bids, a move some industry observers say may be a first among major carriers.
If a flight is overbooked, travelers checking in at an airport kiosk or online see a screen asking them if they'd like to submit a bid for the value of a travel voucher they would take to be bumped. Customers enter a dollar amount. Delta makes clear that it accepts lower bids first.
While Delta previously asked for volunteers by offering a specific amount in vouchers --- say, $200 --- the new system requires travelers to name their price. The bidding methods could burn inexperienced travelers who offer a low bid. Experienced travelers, meanwhile, may find themselves undercut in the effort to collect vouchers.
Delta benefits because the system could mean smaller amounts being paid out in compensation and thus lower costs for overbooking and bumping.
Delta spokesman Anthony Black said the bidding system also cuts down on the time gate agents spend sorting through volunteers, which should speed boarding and cut down on delays.
"I think it's a great system, " said Charlie Leocha, director of the Consumer Travel Alliance. "It's a pecking order created by consumers. The only negative would be when the consumers allow the pecking order to be built on ignorance and they don't understand what their rights are." He also said passengers should be aware of any limits on voucher use.
Some people may still wind up being involuntarily bumped, which happens when a flight is still overbooked after volunteers are solicited.