A major flight outage across the US on January 11 was caused by a worker accidentally erasing computer files, according to the Federal Aviation Administration (FAA).
The regulator said in its preliminary review of the incident that it had "determined that contract personnel unintentionally deleted files while working to correct synchronisation between the live primary database and a backup database".
The FAA ordered the grounding of all US flights on January 11, an outage that lasted several hours, and saw upward of 11,000 delays and around 1,300 cancellations.
The regulator said it has "so far found no evidence of a cyber-attack or malicious intent" but added it "continues to investigate the circumstances surrounding the outage".
"Necessary repairs" have been undertaken to bolster the "robustness" of the system, the FAA said.