The Federal Aviation Administration FAA revealed on Thursday what caused a ground stop a week ago that disrupted more than 11,000 flights.
The FAA said that the issue occurred while personnel worked to correct synchronization between the live primary database and a backup database. The Notice to Air Missions NOTAM messaging system was downgraded last week due to a procedural error related to a corrupted data file, according to the agency.
The NOTAM system provides pilots, flight crews, and other users of U.S. airspace with critical safety notices.
The FAA ground stop was not issued until the following morning after the system outage occurred on January 10.
The outage resulted in the first nationwide grounding of departing flights since the Sept. 11, 2001 attacks.
FAA acting administrator Billy Nolen will hold a virtual briefing Friday for lawmakers and staff who have been trying to find out what went wrong.
The FAA was under fire last week by lawmakers who said the computer outage was completely unacceptable and demanded the agency explain how it will avoid future incidents.