This Is the Worst Thing to See On Your Boarding Pass—and No, It’s Not SSSS

Boarding passes contain a lot of helpful information, but a small printed number could be the difference between making your flight and getting left behind. 

While frequent travelers may already be familiar with the SSSS security code (which can trigger additional security screenings), another code—and the order the numbers are in—can have a big impact on boarding. The somewhat hidden clue is in the sequence number, or simply “SEQ” on a boarding pass, which references the order in which passengers can check in for a flight. That order can then be used to determine who is able to board a flight, and who is not.

In fact, that same sequence number can be used to determine whether a passenger gets involuntarily bumped from a flight, according to the U.S. Department of Transportation (DOT).

“If there are not enough passengers who are willing to give up their seats voluntarily, an airline may deny you a seat on an aircraft based on criteria that it establishes, such as the passenger’s check-in time, the fare paid by the passenger, or the passenger’s frequent flyer status,” the DOT wrote on its website.

Passengers who checked in late for their flights shared their experience on social media of being booted off a plane, all because of that check-in sequence order.

“My wife and I [tried] to fly [from Connecticut] to [Puerto Rico]… the flight was overbooked and since we were the last two people to check in we had to wait until boarding was completed to see if anyone No showed,” one traveler shared in a post on Reddit. “Everyone showed up and they told us sorry can’t take ya.”

The passenger said they were able to re-book on a separate airline and keep their original return flight, but were left to fend for themselves when it came to a refund.

The DOT said airlines are required “to give all passengers who are bumped involuntarily a written statement describing their rights and explaining how the carrier decides who gets bumped,” but added that compensation is situational.

To help avoid the unfortunate and stressful situation of being bumped, passengers are encouraged to check in as early as possible for their flights. That is generally 24 hours in advance of the scheduled departure time.

Beyond overbooked flights, checking in on time matters when it comes to things like seat selection. But travelers should keep in mind that check-in cutoff times vary by airline, so it’s important to note each carrier’s individual policy.