What we know so far about why US flights were grounded
4 hours ago
The order to ground all departing US flights was finally lifted after more than five hours. ( AP Photo: Tony Gutierrez )
The United States has lifted its order to ground departing flights nationwide as a major communications outage continues to disrupt air travel.
The Federal Aviation Administration (FAA) cited "extraordinary circumstances and reasons of safety", with the White House blaming outdated air traffic control technology for the outage.
Thousands of flights into and out of the US were delayed or cancelled, leaving airlines and passengers scrambling to work out their next steps.
The ABC understands the US "ground stop" has caused some delays to a small number of US-bound flights from Australia.
Here's what we know about the unfolding situation so far.
US Homeland Security Secretary Markwayne Mullin has attributed the disruption to a telecommunications issue with air traffic control centres.
"It's just a telecommunications outage as of right now," Mr Mullin told reporters at the White House earlier on Friday, local time.
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