Air Traffic Control Equipment Outages

In the summer of 1995, the National Transportation Safety Board was asked to conduct a special investigation into the ongoing computer and related equipment outages experienced by the Federal Aviation Administration (FAA) en route air traffic control (ATC) system. The special investigation focused on the problems that had become visible to the public at the five air route traffic control centers (ARTCCs) with the oldest controller display computer systems. A team of investigators conducted interviews and research at these five ARTCCs and at one terminal radar approach control facility.

This report presents a basic overview of the ATC system and ARTCC computer systems, and discusses the maintenance and repair of aging display computers and the problem of outages involving these and other systems. The report also discusses a few ongoing FAA modernization programs to address these problems. Because of the limited scope (in time and resources) of its investigation, the Safety Board made no attempt to analyze the management of past modernization efforts, nor did the Board attempt to analyze scheduling or financial matters pertaining to current modernization projects.

The centerpiece of the FAA’s efforts to modernize the ATC system was the Advanced Automation System (AAS), which was initiated in the mid-1980s and entirely restructured in June 1994 after a series of schedule slips and cost overruns. The FAA’s current modernization efforts include portions of the restructured AAS. A computer and controller workstation modernization effort that was part of the AAS was scaled back and renamed the Display System Replacement (DSR). Another portion of the AAS, the voice switching and control system, was retained to enhance communications capabilities in en route facilities. The FAA also added a project called the Display Channel Complex Rehost, which will replace the older of the FAA’s two display computer systems (the IBM 9020E) with off-the-shelf hardware until the DSR is implemented. The report discusses these projects as well as the ARTCC Critical and Essential Power System program, which is an upgrade project for facility electrical power systems.

The report concludes that while the en route ATC system is safe, the equipment failures examined have had a detrimental effect on the efficiency of air traffic movement. The report also concludes that the FAA’s plans to upgrade the computer systems will be beneficial.

Safety issues in this report include:

  • The increasing frequency of outages involving the aging IBM 9020E display channel complex equipment;
  • Other recent equipment outages involving power systems and communications equipment;
  • Lack of controller proficiency with the direct access radar channel (DARC)/Standalone mode of the backup computer system;
  • The increased likelihood that some ARTCC computer systems will be operated with compromised redundancy, which increases the risk of outages; and
  • The adverse effect of the retirement of highly skilled airways facilities technicians on the FAA’s ability to maintain and repair many air traffic control systems.

The Safety Board issued safety recommendations concerning these issues to the FAA.


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