A communication breakdown is being blamed for leading to a rare ground stop of all U.S.-based aircraft.
The Federal Aviation Administration (FAA) ordered a nationwide ground stop on all American flights on Friday afternoon.
The problem has been blamed on what was called a "temporary telecommunications outage".
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The FAA said in a social media post that the ground stop, only the third in the States since 9/11, was "out of an abundance of caution".
The outage affected major air route traffic control centres, according to U.S. Transportation Secretary Sean Duffy.
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Detroit Metropolitan Airport has reported that the issue is only affecting departing flights, and not arrivals. Those who are due to fly out of Detroit Metro are urged to check the flight status of their carrier before going to the airport.
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U.S. Department of Homeland Security Secretary Markwayne Mullin told reporters on Friday that there was no evidence of a cyberattack or any other "nefarious" act, and there was no cause for alarm.
The only other nationwide ground stop since 9/11 was in 2023, when the FAA's NOTAM system, which alerts pilots and air traffic controllers to unusual changes or hazards in airspace, went down. This prevented pilots from receiving the necessary pre-departure paperwork.
