FAA reveals what caused computer outage prompting ground stop

The FAA says so far no evidence has been found that the outage was caused by a cyber-attack or malicious intent

The Federal Aviation Administration (FAA) revealed on Thursday what caused a ground stop a week ago that disrupted more than 11,000 flights.

A preliminary review found contract personnel "unintentionally deleted files," disrupting a key computer system on Jan. 11.

The FAA said the issue occurred while personnel were working "to correct synchronization between the live primary database and a backup database." 

The FAA said it "has so far found no evidence of a cyber-attack or malicious intent."

TRAVELERS FUME AS FAA ISSUES NATIONWIDE GROUND STOP: 'THIS IS INSANE'

Passengers wait in terminal as FAA system outage causes flight delays, cancellations

Passengers wait to depart Chicago's Midway Airport as flight delays stemming from a computer outage at the Federal Aviation Administration has brought flights to a standstill across the U.S. Wednesday, Jan. 11, 2023, in Chicago.  (AP Photo/Charles Rex Arbogast / AP Newsroom)

Last week, the agency said the computer outage of the Notice to Air Missions (NOTAM) messaging system was caused by a procedural error related to a corrupted data file. 

The NOTAM system provides pilots, flight crews and other users of U.S. airspace with critical safety notices.

The system outage occurred on Jan. 10, but the FAA ground stop was not issued until the following morning.

O'Hare passengers during ground stop

Passengers wait for the resumption of flights at O'Hare International Airport after the Federal Aviation Administration (FAA) had ordered airlines to pause all domestic departures due to a system outage, in Chicago, Illinois, U.S., January 11, 2023.  (REUTERS/Jim Vondruska / Reuters Photos)

FAA LIFTS AIRLINE GROUND STOP AS FLIGHT DELAYS, CANCELLATIONS PILE UP ACROSS THE COUNTRY

The outage led to the first nationwide grounding of departing flights since the Sept. 11, 2001, attacks.

FAA acting administrator Billy Nolen plans to hold a virtual briefing Friday for lawmakers and staff who have sought details of what went wrong.

Travelers wait to hear if their flight will depart on time, at Los Angeles International Airport in Los Angeles, on January 11, 2023

Travelers wait to hear if their flight will depart on time, at Los Angeles International Airport in Los Angeles, on January 11, 2023.  (STEFANI REYNOLDS/AFP via Getty Images / Getty Images)

PILOTS SAY FAA COMPUTER OUTAGE THAT GROUNDED US FLIGHTS NATIONWIDE UNPRECEDENTED

The FAA came under fire last week by lawmakers saying the computer outage was "completely unacceptable" and demanded the agency explain how it will avoid future incidents.

Reuters contributed this report.