In order to avoid a repeat of the computer system failure that on January 11 caused the cancellation of more than 11,000 U.S. flights, the Federal Aviation Administration (FAA) informed lawmakers that it had implemented a number of adjustments.

In a letter dated Friday and obtained by Reuters on Monday, Acting FAA Administrator Billy Nolen stated that the agency has changed the system to stop a damaged file from harming a backup database.

The FAA informed legislators last week that contractor staff members who unintentionally removed files from the Notice to Air Missions (NOTAM) database had had their access to a pilot message database terminated.

Nolen’s letter said attempts to restore those files contributed to the outage and since then the FAA had adopted a one-hour delay in synchronizing databases that should prevent data errors from immediately reaching the backup database.

The FAA also said it “now requires at least two individuals to be present during the maintenance of the NOTAM system, including one federal manager.”

Reuters reported some of the upgrades earlier. The FAA action was the first nationwide groundstop of departing flights since the Sept. 11, 2001, al Qaeda attacks on the United States.

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

The NOTAM System consists of two interdependent systems, the FAA letter said, the legacy U.S. NOTAM System, which is 30 years old, and the newer Federal NOTAM System, which it called the foundation for the ongoing modernization effort.

The primary database and a backup database are located in Oklahoma City, Oklahoma, while two additional backup databases are in Atlantic City, New Jersey.

The FAA began modernizing the NOTAM system in 2019 “and is scheduled to discontinue the legacy U.S. NOTAM System by mid-2025. Phase two of the NOTAM system modernization is planned to be completed in 2030,” the letter said.

The FAA said it has conducted three assessments of the system since 2020 including the most recent in October.