Last week’s massive flight disruption that grounded thousands of planes was caused after “contract personnel unintentionally deleted files,” the Federal Aviation Administration said Thursday.
On Jan. 11, the FAA halted all departures nationwide after an outage to the Notice to Air Missions, or NOTAM, system.
The FAA said in a statement that the files were deleted by accident as the contractors were "working to correct synchronization between the live primary database and a backup database."
The review was described as preliminary, and the incident is still under investigation. The FAA said it has found no evidence of a cyberattack or malicious intent.
The NOTAM system sends pilots vital information they need to fly. The system was restored later that day.
On Jan. 11, the FAA sent out a tweet at 7:20 a.m. ordering the airlines to pause all domestic departures until 9 a.m.
The FAA lifted the ground stop around 8:50 a.m., and normal air traffic operations began resuming gradually.
The agency said Thursday that repairs have been made to make the system more resilient and that it will adopt other steps.