European air traffic management organization Eurocontrol has resumed normal operations following a software misalignment that caused its Enhanced Tactical Flow Management System (ETFMS) to fail for several hours April 3, causing delays to thousands of flights in Europe.

“The trigger event was an incorrect link between the testing of a new software release and the live operations system; this led to the deletion of all current flight plans on the live system. We are confident that there was no outside interference,” Eurocontrol said April 4.

The Brussels-based air traffic management (ATM) organization, which serves as Europe’s “network manager,” could not immediately say how many flights were delayed by the outage of the capacity/demand-balancing system. It had said earlier that it expected 29,500 flights within Europe, and that half could be delayed.

The ETFMS system compares traffic demand and available capacity in air traffic control (ATC) sectors based on flight plans filed by aircraft operators. It then assigns air traffic flow management slots through computer-assisted slot allocation. In over two decades of operation, the system has experienced only one other outage, which occurred in 2001, Eurocontrol said.

After first reporting the ETFMS failure on April 3, Eurocontrol said it implemented contingency procedures that would reduce European network capacity by about 10%. The agency then announced that it had identified the issue and requested aircraft operators to refile any flight plans that were originally filed before 10:26 UTC.

Eurocontrol said that as of 15:20 UTC, access to the ETFMS system had been restored, but it continued using contingency procedures. As of 18:00 UTC, the agency resumed normal flow-management operations in coordination with airlines, airports and ATC facilities.

Eurocontrol previously has said it will implement “network predictability improvements” to the flight activation monitoring (FAM) function of the ETFMS system beginning this autumn. Through FAM, the system can shift flights in time that are not reported as airborne after their expected takeoff time and possibly suspend flights that are still not reported as airborne after a certain time parameter.

Plans call for gradually reducing the 30-minute FAM parameter in three steps of five minutes each, so that a flight would be suspended after 25, then 20, then 15 minutes after the expected takeoff time.

Bill Carey,