Being involuntarily denied boarding - ie being bumped off a flight - is rare, but can be massively inconvenient if/when it happens.

In this article series we explain the issues about what being bumped is, how to minimize your chances of being bumped, and how to ensure you get full fair compensation if you do get bumped.

Why and How Airlines Overbook Flights A sometimes unfairly condemned activity that usually works to your advantage
	The flipside of full flights can be an increased chance of finding yourself with no seat, due to the flight being oversold. Part of a series on being bumped from flights, see the other articles in this series listed on the right.

Airlines are experiencing massively increased rates of involuntary denied boarding compared to earlier this decade, while at the same time, the proportion of passengers willing to voluntarily accept denied boarding has plummeted.

While you're still statistically unlikely to be involuntarily denied boarding, the ugly industry trends towards fewer and fuller flights could make the consequences of any such problem much harder for you to positively resolve.

This first part of our series on what is commonly referred to as 'bumping' puts these issues into their overall context.

Why Airlines Overbook Flights

Most airlines will overbook their flights, sometimes by as much as 50%.  This means that if they have a 150 seat airplane, they might sell 225 tickets for that flight - a mix of all different fares.

They do this for two reasons.

Not everyone travels on their booked flight

Firstly, the airlines know that not everyone who has booked to travel on any specific flight will actually travel on that flight.  Various reasons can mean people don't show up for the flight.  A person might arrive at the airport early and fly out on an earlier flight.

A business traveler might have made duplicate bookings on multiple flights so that he has the certainty and flexibility to travel on whichever flight becomes the most convenient for him.  Someone else might become sick and unable to travel.  And some people might be doing a 'back to back' itinerary and have no intention of traveling on the ticket, even though they've booked and paid for it.

(Please see our article series on Airfare Loopholes for an explanation of back to back ticketing and other ways to beat the airlines at their own games.)

So, for whatever reason, airlines know that not every booking for any flight will result in the person for sure turning up to travel.  By keeping careful historical records of past similar flights, and matching it to all sorts of other variables including such things even as the weather at the departure and arrival points, relevant holidays, other flight cancellations, and all sort of things, they have developed reasonably accurate forecasting models to give guidelines for what percentage of travelers booked on a flight will actually travel and what percentage will not travel.  This information allows them to accept a number of overbookings with equanimity, and usually with few problems.

Selling more seats earns the airline more money (of course)

The second reason the airlines do this is simply to make more money.

If an airline can sell 225 tickets on a flight that uses a plane with only 150 seats, obviously it stands to make more money than if it restricts itself to selling only 150 tickets.

But this is not just a selfish venal act on the part of the airlines that we should decry.  Read on...

Overbooking is a Good Thing

Now here's an interesting concept to keep in mind.  Sensible responsible overbooking (assuming these are not conflicting concepts!) is a good thing, because it enables the airline to accept lower fares for the seats they are overbooking.

If an airline says to itself 'I need to earn $15,000 from this flight' and if it has 100 seats on the plane, it needs to get an average of $150 a ticket if it sells 100 tickets.  But if it says 'I'm going to oversell the flight' and if it sells 150 tickets - ie, by overselling the flight by 50% - it only needs to get an average of $100 per ticket.

So overselling, if it is done correctly (ie - as long as it doesn't result in passengers not being able to take the flights they've booked and paid for), can help us all to get lower airfares, and so is a good thing.

Overbooking can also be a good thing if you can take advantage of an airline's request for volunteers to accept being bumped off a flight in return for a 'bribe' - usually either a voucher good for some hundreds of dollars off a future flight, or a free flight voucher.

Why Overbooking Sometimes Goes Wrong

No matter how exact and scientific an airline's overbooking model is, there is still an element of random chance, and an additional element of impossible-to-anticipate other variables.

For example, an unexpected flight disruption by another airline might suddenly cause a surge of extra people seeking to travel on a flight, disrupting the airline's careful projection.  Weather cancellations and other operational disruptions can also mess up an airline's projections for passenger numbers.

And then, sometimes, an airline's 'run of luck' simply turns bad.  Just like if you throw a pair of dice enough times, every so often you'll get a double-six appear; so too, if you bet on overbooking statistics enough times, every so often, your bet will go wrong.

Furthermore, these days, airlines are feeling the need to overbook more aggressively than before, because they need as much money as possible per flight, so they are choosing to reduce the safety margin and to overbook in greater numbers, thereby of course increasing the risk that a flight might end up with too many people turning up at the gate seeking to travel.

How Often Does Overbooking Go Wrong

Surprisingly, it is fairly easy to answer this question, and moderately exactly.  The Department of Transportation issues quarterly data showing the number of passengers who both accept voluntary inducements to not take the flight they were booked on, and the number of passengers who are forced to take a later flight, whether they wish to or not.  You can see their latest reports here.

This information is of course only as accurate as the reporting from the airlines, and there are a number of 'exceptions' - cases where an airline not accepting a passenger's booking doesn't formally count as an overbooking denial.  But the information is the best there is and is definitely helpful.

For the period January - March 2009 (the most recent quarter available at the time of writing this article) you had the least chance of being involuntarily denied boarding on a Jetblue flight (who bumped no passengers at all against their will), and most chance of being moved off your flight with Atlantic Southeast Airlines (who were bumping 3.94 of every 10,000 passengers).  American Eagle and Comair were the two next worst offenders.

In round figures, and on average, currently about 1.3 passengers per 10,000 passengers are denied boarding against their wishes, and for every involuntary denied boarding person, there are about nine other passengers who have volunteered to be bumped, accepting some form of inducement in the process from the airline.

Part of a series on being bumped from flights, see the other articles in this series listed on the top right.

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Originally published 17 Jul 2009, last update 30 May 2021

You may freely reproduce or distribute this article for noncommercial purposes as long as you give credit to me as original writer.