Southwest Airlines faces another round of disruptions today as a computer glitch caused the airline to ground hundreds of flights across the country. The airline requested the FAA pause their operations, citing a problem with one of their internal systems. It appears to be a firewall failure that disrupted data connections.

The glitch appears to be brief. Based on the FAA Twitter account, it lasted approximately 40 minutes. But the carrier is facing delays across the entire network, as all flights were affected. Southwest will be playing catch-up all day.

In the wake of the disruption, Southwest Airlines issued a statement apologizing to its customers for the inconvenience.

Why is this worrisome?

The incident is reminiscent of December’s disruption, when the airline’s crew scheduling system effectively stopped functioning during a spate of bad weather. This caused a widespread network failure, and forced the cancellation of more than 15,000 flights during the month, the majority around the Christmas holidays. That incident cost the airline millions of dollars and led to a public apology from Southwest’s CEO.

What’s at stake is the overall reliability of the airline. Airlines are utterly dependent on technology to manage their operations, and Southwest is way behind the curve when it comes to modernizing their systems. Their computer systems are ancient. An upgrade has been needed for years. Southwest simply hasn’t dealt with it yet. Hopefully, this will be yet another prompt for them to do so.

For now, Southwest Airlines will be dealing with more unhappy customers in the aftermath of the latest disruption. Rebuilding consumer confidence is important, and they more incidents like this that occur, the harder it will be for them.