What was behind the sudden halt to thousands of domestic flights yesterday morning? Today on Post Reports, a conversation with transportation reporter Lori Aratani about a highly unusual aviation system failure and the deeper flaws it exposed.

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More than 4,600 flights arriving in and out of the U.S. faced unusual delays yesterday morning, as aviation staff sought answers to an unexpected overnight outage of its airspace alert system.

Preliminary reviews traced the problem to a damaged database file, but the sweeping stoppage that ensued was something the United States hadn’t experienced since the Sept. 11, 2001 terrorist attacks.

This mass grounding of flights also came shortly after a messy holiday travel period: failures at Southwest Airlines prompted more than 16,000 flight cancellations.

Combined, the logjams and stoppages point to a deeper problem with America’s very fragile aviation system, explains The Post’s Lori Aratani.

“This is just another sign of how we need to invest in infrastructure,” Aratani told Post Reports.