Comedian Louis CK has absolutely no patience for the complaints of airline passengers, as he explains in one very funny, albeit profanity-laced bit. "People on planes, they complain," he says. "They get off the plane, they come to your house, and they tell you about their whole flight experience…. 'That was the worst day of my life! I had to sit on the runway for forty minutes!'… People will stop doing the dishes and turn around and go, 'Oh my God, really? For forty minutes? That's awful! You should sue them.'"

He is exaggerating for effect, of course, but you can still expect that this Labor Day Weekend lots of people will be complaining to their friends about their flight experiences, and the biggest of these complaints will be about cancellations.

Last year, there were almost 62,000 flights scheduled for Labor Day weekend, and just over 500 of them were cancelled, according to the Bureau of Transportation Statistics. This year, even more people (roughly 14 million) are expected to fly, and the cancellation rate most likely will be about the same. Short of the airlines offering cancelled passengers overly generous compensation, like a free round-trip flight to Sydney, none of them will be happy about it. Even in the midst of a major thunderstorm, passengers will still complain about cancellations. And when there is no obvious cause for the problem, passengers get even more frustrated, accusing the airlines of being incompetent and self-serving.  

It may seem like the airlines are just out to make your life hell. But as a professor of industrial and operations engineering who has studied the industry for 20 years, I’ve learned that cancellations are rarely good for the airline industry except when they are also actually good for passengers.

Airlines don't cancel flights to save money. They cancel flights to prevent wider cancellations and delays.

 “They do this all the time!" I often hear people complain after a flight is cancelled. "If there aren’t enough passengers to make it worth their while, they just cancel the flight to save money.” The idea that airlines could benefit from such cancellations, at the expense of their passengers’ convenience, may seem like a logical argument if you think of a single flight in isolation. But what makes the airline industry so complicated, and often so confusing for its passengers, is that flights don’t exist in isolation, they are part of a complex system.

Consider, for example, the following picture:

This map shows the route taken by a single passenger jet over the course of a single day (October 11, 2013). Aircraft N654SW started the day in Providence and then flew to Baltimore, Newark, Norfolk, Atlanta, Austin, Dallas, Amarillo, Denver, Salt Lake City, and Oakland before finally ending the day in Ontario, California.

If you were to cancel the flight from Baltimore to Newark because there weren’t enough passengers, you might save the fuel cost of flying from Baltimore to Newark, but you would also create a downstream problem—there would be no airplane in Newark for the flight to Norfolk, no plane in Norfolk for the flight to Atlanta, and so on. (Even when you factor in the long-haul trans-continental flights, an average plane covers almost 4.5 flights a day, visiting roughly 3.5 unique cities.)

To make things even more complicated, the pilots and flight attendants don’t always stay with the same aircraft all day long. The crew starting off in Baltimore might only be able to fly as far as Denver before they run out of legal flying hours. They would then be scheduled to spend the night in Denver before piloting the flight from Denver to Chicago the next morning. If you cancel their trip into Denver tonight, you won’t have a crew for the Chicago flight tomorrow morning.

Be grateful if you live near a major airport—unless that airport is LaGuardia.

With rare exceptions, like the business meeting you wanted an excuse to miss, passengers are never happy to have their flight cancelled. But it may be good for you to have someone else’s flight cancelled. In particular, strategically cancelling a small number of flights and inconveniencing a small number of passengers can prevent delays and other hassles for a far larger number of passengers.

Consider that airplane flying from Baltimore all the way through to Ontario. Airlines try to limit the amount of buffer time in between flights because an airplane sitting on the ground is a very expensive wasted asset. So if the Baltimore-to-Newark flight has a one-hour departure delay due to a mechanical problem, this delay is likely to propagate to the next flight, and the next one, and the next one.

But suppose that instead of going from Baltimore to Newark to Norfolk, that plane was scheduled to fly from Baltimore to Newark and then back to Baltimore before continuing on to Atlanta. In this case, what if you cancelled the out-and-back flights from Baltimore to Newark and then Newark back to Baltimore? By the scheduled departure time of the third flight (Baltimore to Atlanta), the mechanical problem would be fixed, the crew and aircraft would be in the right location, and the rest of the day could operate as scheduled. Two flights’ worth of people would be disrupted instead of ten.

This is, in fact, what frequently happens. The following table shows the probability of your flight being cancelled as a function of your destination, based on data from 2009 to 2013. Of the 35 U.S. airports with the highest percent of their inbound flights being cancelled, all but one of them average fewer than 15 total inbound flights a day, with 29 of these averaging fewer than five. (The one exception, perhaps not surprisingly, is LaGuardia, with an average of more than 10 of its roughly 275 domestic arrivals per day being cancelled.) This is bad news if you’re flying to places like Mammoth Lakes, California; Kodiak, Alaska; Dubuque, Iowa, and other smaller airports. These are typically airports that an airline will serve by flying out-and-back from a larger airport, often with smaller aircraft, making it easier to cancel without significantly disrupting other parts of the system (you’ll also note that many of these locations are prone to bad weather). 

Cancelling flights is a lot harder than it used to be.

The justification for strategic cancellations is cold comfort to the unlucky travelers whose flights have been axed. How do airlines re-accommodate them?

Years ago, this was not always so difficult. "Load factors," essentially the percent of seats on a plane that are occupied, were much lower than they are today. In the past decade alone, they’ve risen from an average of 70 percent to nearly 85 percent, as the following table shows:

In addition, destinations were often served more frequently, so cancelled passengers could be re-booked onto a later flight that day.

Today, this re-booking is much harder to do. When fuel prices (the airlines’ largest marginal cost) soared, the industry couldn't survive with so many empty seats, so it cut capacity. Not only did this mean fewer flights to re-accommodate disrupted passengers, but the remaining flights themselves had fewer available seats. Over the past decade, capacity has crept steadily tighter and tighter. This doesn’t just mean that you are less likely to have an empty middle sit next to you (in fact, you’re much more likely to be sitting in the middle seat now!). It also means that when a flight gets cancelled, it’s harder to find a way to re-book its passengers.

For example, suppose you have a flight that’s 80 percent full and you cancel it. You would need roughly four more flights to the same destination before you could re-accommodate everyone. If your flight was 95 percent full, then it would take 19 flights before everyone could be re-booked. As a result, the airlines are less likely to cancel flights for the sake of reducing delay propagation, recognizing that they have fewer options to rebook passengers. 

Here's how to avoid a cancelled flight—and the best way to get re-booked.

There will always be weather disruptions, mechanical problems, and airspace congestion that make it impossible to fly safely on time, and it may seem like cancellations are rampant. But they are actually still quite rare. In the last five years, just over 1.5 percent of U.S. domestic flights were cancelled. Roughly, this means that someone who flies round-trip non-stop flights every single week would expect to face only one cancellation a year.

What's more, you can improve your chances of flawless travel by flying early in the day, taking non-stop flights, and choosing an airline with many different flights to your destination.

If your flight is cancelled, going to your airline’s website or calling their customer service number can get you re-booked faster than standing in line at the gate. Knowing in advance what other flight options would work for you can make the process smoother and help you nab one of the best options before others snatch them up (instead of “My flight just got cancelled, I need a new one,” try “Can you get me onto Flight #1539  leaving at 10:56?”). And let the re-booking agents know if you can be flexible. For example, if your flight to Boston is cancelled, other flights to Boston are filling up quickly as your fellow passengers are re-booking. But if you are willing to fly to Providence instead, there may be plenty of capacity on a flight leaving soon.

But perhaps the best advice is to keep a cool head about your cancelled flight rather than complaining about it. After all, you're partaking in what Louis CK rightly calls "the miracle of human flight."