Chicago aviation expert weighs in on United's nationwide ground stop

United Airlines has resumed its flights after experiencing a nationwide ground stop on Tuesday, citing a system-wide technology issue that affected passengers, flight crews, baggage handling, and connecting flights.

"United is one of the largest global airlines. Essentially no takeoffs allowed for an hour – that really affects the operations," said Joe Schwieterman, aviation expert, DePaul University.

As travelers returned home from Labor Day weekend plans, a midday outage sent the carrier scrambling.

"We have pilots that have hours-limits, we have airplanes that need maintenance, you have people missing connections, you can’t hold international flights much longer because of timing issues, so they’re going to deal with kind of a mess that comes out of this," said Schwieterman.

Schwieterman says initial details about the outage point to an internal issue, not a cyber-attack.

A United Airlines spokesman said, in part: "Earlier today a software update caused a widespread slowdown in United's technology systems."

"What’s frustrating is that airlines build in redundancies to prevent this very type of thing, even a 5-minute delay on a system is vast, and once again, the systems failed us," said Schwieterman.

Flights that were already airborne were allowed to continue, but United Airlines requested that the Federal Aviation Administration halt all of its planes due to the technology glitch.

The ground stop last roughly an hour, with flights resuming normal operations just before 1 p.m.

"Here it’s really clear, it was an internal problem with United, not the weather, not something the federal government caused, so it’s a pretty clear line of responsibility and I think United will be trying to make amends with a lot of passengers that were affected," said Schwieterman.

While United Airlines stated that it does not believe this to be a cybersecurity issue, they are still investigating.

The U.S. Department of Transportation is also looking into the disruption and encouraging all affected travelers to visit for further information.