A three-hour air traffic control outage that grounded hundreds of flights across the West on Tuesday also led to five close calls in which planes failed to keep the recommended minimum distance between each other, the Federal Aviation Administration said Wednesday. In two incidents, planes that were not able to get information on the proximity of other planes had their collision avoidance alarm systems go off, according to the National Air Traffic Controllers Association. That would require pilots to take evasive action, it said.
The FAA said it doesn’t know yet whether evasive action was required. It said that although radio contact failed, radar coverage remained fully operational and aircraft were safely handed off to other air traffic control facilities. According to the FAA’s Paul Turk, the shutdown of radio communication in the West was caused by failure to perform a routine maintenance check on the communication system for the region that covers California, Arizona, Nevada and parts of Utah. The communication system shuts down if the check is not performed every 30 days. A backup system exists, but it failed, too, because it “was not configured properly,” the FAA told USA Today.