For hours the world’s largest aircraft fleet was grounded by an outage in the government system that had delayed or canceled thousands of flights throughout the US, on Wednesday.

Currently the White House said there is no evidence of a cyberattack behind the outage that ruined travel plans for millions of people. On Wednesday morning, President Joe Biden said that he has directed the Department of Transportation to do an investigation.

This outage revealed how much the world’s economy depends on air travel, and how much air travel depends on NOTAM (Notice to Air Missions System). The NOTAM system broke down late Tuesday and led to 1,000 flight cancellations and more than 6,000 delayed flights.