A software update was to blame.

By Michal Addady / Fortune
August 18, 2015
Credit: Getty Images

A software upgrade at an air traffic control center in Virginia went terribly wrong on Saturday, leading to 492 delayed flights and 476 cancelled flights, the U.S. Federal Aviation Administration told The Guardian.

Reagan National Airport was forced to cancel 50% of inbound flights and 42% of outbound flights; their delays averaged about 3 hours. Similarly, 58% of inbound flights and 36% of outbound flights were cancelled in Baltimore with average delays of over an hour.

The upgrade was performed on the En Route Automation Modernization (ERAM) satellite-based computer system for air traffic management, a new computer system implemented by the FAA in March of this year.

The administration posted a statement on Facebook saying that the update was meant to provide air traffic controllers with additional tools. They have assured consumers that they disabled the new features while they assess the issues.

This article originally appeared on fortune.com.