The US has blamed the third-party contractors for last week's mega outage that grounded thousands of flights, saying that "contract personnel unintentionally deleted files" while working on the 30-year-old software.
In a statement, the US Federal Aviation Administration (FAA) said that the files were deleted "while working to correct synchronisation between the live primary database and a backup database".
"The agency has so far found no evidence of a cyber-attack or malicious intent. The FAA continues to investigate the circumstances surrounding the outage," it added.
A glitch in the FAA software, which grounded thousands of flights in the country earlier this week, is at least 30 years old and six years away from being updated.
The aviation administration said it has made the necessary repairs to the system and has taken steps to make the Notice to Air Missions (NOTAM) system "more resilient".
The agency is acting quickly to adopt any other lessons "learned in our efforts to ensure the continuing robustness of the nation's air traffic control system".
As a result of the massive nationwide technical glitch, more than 10,000 flights in and out of the US were delayed, while more than 1,300 others were cancelled.
CNN reported that the core operating system for the database has been around since the 1990s.
"Regardless of the improvements made to the system in recent years, it still has the heart of an 89-year-old man," a government source was quoted as saying in the report.
President Joe Biden had called for a "full investigation" into the incident.