The US Federal Aviation Administration has lifted the longest nationwide ground stop of flights since the 11 September 2001 terrorist attacks.
The FAA said Friday's stoppage, which lasted more than four hours, was "due to extraordinary circumstances" from a communication issue affecting all air traffic control centres.
Homeland Security Secretary Markwayne Mullin said there was no indication of an attack and that everybody was safe.
The ground stop led to more than 8,500 delayed and nearly 8,000 cancelled flights on Friday, according to FlightAware.
The FAA's initial announcement at 15:54 EST (20:54 GMT) said all flights departing within the US would be grounded until further notice.
More than 3,500 airplanes were in the air at the time. Some were diverted to other airports and others flew on to their destinations.
Hours later, some flights were allowed to take off from San Francisco International airport.
The Federal Aviation Administration opened skies again at until 20:15 EST.
All US-bound air traffic from Eurocontrol member states was suspended "on request of the FAA due to technical issues", according to Eurocontrol's website.
There are 42 Eurocontrol member states, including dozens of EU nations, the UK, Ukraine, and Turkey, as well as Israel and Morocco.
Australia's largest international airport, Sydney, grounded all US-bound flights until further notice.
