The FAA has made improvements to the En-Route Automation Modernization (ERAM) air traffic system after a U.S. Air Force U-2S surveillance aircraft, transiting through Southern California airspace at high altitude, triggered a computer shutdown and forced a temporary ground stop at Los Angeles International (LAX) airport.

The incident, which occurred shortly after 3 pm Pacific on April 30, caused the cancellation of around 50 flights outbound and inbound to LAX as well as delaying a further 455 flights around the country. The FAA says the ERAM "experienced problems while processing a flight plan filed for a U-2 aircraft that operates at very high altitudes under visual flight rules (VFR). The computer system interpreted the flight as a more typical low altitude operation, and began processing it for a route below 10,000 feet."

The issue is believed to have been exacerbated by a large number of waypoints in the flight plan for the U-2S which was on a regular training flight and passing through airspace controlled by Los Angeles Air Route Control Center in Palmdale, Calif, at around 60,000-ft. However sources also indicate that an error in a new software load in the control center misinterpreted the location of the U-2S flying VFR at that altitude. "The extensive number of routings that would have been required to deconflict the aircraft with lower-altitude flights used a large amount of available memory and interrupted the computer’s other flight-processing functions," says the agency.

ERAM, which is part of a $2.2 billion air traffic management modernization program, is designed to increase capacity by enabling controllers to track up to 1,900 aircraft simultaneously over a broader area. The system processes data from 64 radars, versus 24 in the legacy air traffic system, and connects en route centers, along with automated flight service stations and the FAA’s Command Center in Herndon, Va., to FAA air traffic sites including Terminal Radar Approach Control (Tracon) facilities and airport control towers.

The FAA says it "resolved the issue within an hour, and then immediately adjusted the system to now require specific altitude information for each flight plan. The FAA also has enabled facilities that use the computer system to significantly increase the amount of flight-processing memory available." The agency says it is now "confident these steps will prevent a reoccurrence of this specific problem and other potential similar issues going forward."