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The chaos that left tens of thousands of Delta passengers stuck in airports around the planet overnight was the result, the airline claims, of a power outage in Atlanta that crippled its computer systems and operations.

But it may not be that simple.

The power company that provides Delta’s electricity disputed that explanation in a statement to NBC News on Monday, and an air travel expert described what could be a far more complex problem rooted in the company’s sprawling collection of internal systems and the proliferation of airline mega mergers.

In the statement, Georgia Power spokesman John Kraft said that a piece of electrical equipment “on their (Delta's) system” was to blame for the outage.

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“Our crews responded to the site this morning and we continue to work with the team at Delta,” the statement said. “Other Georgia Power customers were not affected by the issue with Delta's equipment.” (Citing an ongoing investigation into the cause of the outage, a Delta spokesman declined to comment.)

The travel expert, FareCompare CEO Rick Seaney, told NBC News that airlines have thousands of systems — flight management and passenger reservation, for instance — some of which date back to the 1970s and ‘80s and have never been upgraded.

U.S.-bound Delta passengers at Rome's Fiumicino Airport waited more than an hour in line to check-in early Monday. @ghostdog310 / Twitter

“Only recently airlines have been flushed with cash,” Seaney said. “There hasn't been a lot of cash to add into their infrastructure.”

For airlines that have merged or been acquired, such as Delta, which joined with Northwest in 2008, it can be “very difficult” to keep that infrastructure up to date, Seaney said.

Another failure could come in the next few months, Seaney said, when US Airways and American Airlines — which completed a merger last year — is expected to switch over to the latter’s systems, he said.

“There literally could be 1,000 systems at US Air that have to be migrated over,” he said. “If they miss just one of them it could wreak all sorts of havoc.”

Seaney added that a far more simple culprit — human error — could also be to blame. Either way, he said, Delta should have been prepared.

“There's no doubt that a Fortune 500 company should have backup systems that kick in for these problem[s],” he said. “If they don't, it should be somebody's head at the airlines.”

The Delta spokesman told NBC News that the company does have a backup system, but that after the power loss some of its critical systems and network equipment didn't switch over to the backup.

Citing the investigation, the spokesman declined to provide additional details.