U.S. air traffic experienced a near halt on Friday after the Federal Aviation Administration ordered a nationwide ground stop for departing flights that lasted more than five hours.

The FAA lifted the ground stop at 8:15 p.m. ET, after thousands of flights were cancelled and airports across the country became packed with stranded, irritated passengers.

The unexpected and highly unusual alert was issued at 3:54 p.m. ET, “due to extraordinary circumstances and for reasons of safety.” The alert contained no other information beyond stating that “all departing traffic should remain ground stopped until further notice.”

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“Inbound international flights will be managed on a case by case basis,” the FAA had said.

Transportation Secretary Sean Duffy said in a White House news conference Friday evening that the ground stop was sparked by “instability for our radar and our communications in our centers, in our TRACONS throughout the country.”

TRACON stands for Terminal Radar…