The Federal Aviation Administration (FAA) has declared a major malfunction of its pilot warning system that delayed 10,000 flights, stating that the entire problem was due to a contractor accidentally deleting files.

In a statement, the agency said its “evaluation of the Notice to Air Missions (NOTAM) system malfunction last week determined that contract personnel inadvertently deleted files while they were in the process of correcting synchronization between the live primary database and a backup database.” The NOTAM system delivers safety warnings to pilots, and its failure caused chaos in the aviation industry.

The FAA did not provide additional details, but reiterated that there was no evidence that a cyberattack caused the problem — though it is still investigating. The FAA also said it kept lawmakers from both parties informed of its Thursday investigation.

Airline executives had their own take on the root causes of the NOTAM outage, complaining that the system outage was due in part to a poorly funded and understaffed FAA.

CNBC quoted Delta CEO Ed Bastian, who said in an appearance on Squawk Box that he blames what happened “on the fact that we don’t [the FAA] the resources, the funding, the staff, the tools, the technology they need.”

Speaking on a United Airlines earnings call on Wednesday, UA CEO Scott Kirby said he hoped “this will be the call to our political leaders in Washington that we need to do better.” According to Kirby, the failure and ensuing chaos “should be a wake-up call to all of us in aviation, something many of us in aviation have been saying for a long time…the FAA needs more resources.”

The FAA’s statement that the outage was caused by a contractor inadvertently deleting files suggests that there were issues with the agency’s internal processes and oversight. However, the agency’s response may also point to a need for more resources to help maintain and improve systems.