US Transportation Secretary Sean Duffy said Friday's nationwide airspace shutdown was caused by a faulty router or contractor error during work to replace old copper telecommunications lines with fiber at an FAA facility.
Investigators are still determining the exact cause. The failure disrupted radar feeds and communications with aircraft, generating more than 1,000 connection attempts every four to five seconds.
The ground stop lasted over four hours and disrupted more than 15,000 flights by Friday night. More than 3,600 additional flights were canceled on Saturday. Duffy said the incident exposed the vulnerability of the FAA's aging infrastructure and called on Congress to fund a major overhaul of the air traffic control system.