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New Life for Aging Systems

Re-engineering helps keep the Atmospheric Early Warning System vital in a new century

By Hugh Spence, Ph.D., and Terry McDaniel

Terry W. McDaniel, left, and Hugh F. Spence, Ph.D. oversee an SwRI program to maintain and update radar display consoles, like the one shown here, for the Atmospheric Early Warning System. Spence is a technical advisor and retired Institute Engineer with the Avionics and Support Systems Department of the Aerospace Electronics and Information Technology Division. He has design experience with special purpose analog and digital systems, signal processing, and testing and calibrating aircraft flight control components. He has extended the life of military electronics systems by providing design analysis and redesigns for vacuum tube, transistor, electromechanical and other older technology systems. McDaniel, a research engineer with the Avionics and Support Systems Department, is a hardware designer with experience in autopilots, unmanned aerial vehicles and various other aircraft avionics systems.

Computer technology has grown exponentially since the 1970s, and many generations of hardware, software and even manufacturing techniques have disappeared as processors have become more capable and compact. However, there are electronic systems dating to the 1970s that continue to provide valuable service adequate to their task. One such system, the U.S. Air Force Atmospheric Early Warning System (AEWS), remains a vital link in the electronic network that watches the skies for potential threats to homeland security.

Maintaining the AEWS computers is a two-edged sword. On the one hand, the consoles must be kept functional and up-to-date as technological improvements permit. On the other hand, the improvements must fit into existing infrastructure, and operating procedures must remain familiar enough to avoid costs and outages associated with re-training AEWS operators and maintenance personnel.

Computer engineers at Southwest Research Institute (SwRI) were asked to examine electronic circuitry from aging AEWS consoles and reverse-engineer replacement parts and procedures to improve reliability, increase capability and add function to the system, while maintaining seamless operation. Once begun, the operation soon resembled re-engineering more than reverse engineering.

Fighter aircraft are prepared to respond to airborne threats detected over the United States and Canada by the U.S. Air Force Atmospheric Early Warning System (AEWS). Radar consoles used by the AEWS contain electronic components, such as the circuit board shown above, that are becoming increasingly hard to repair or replace. Fighter aircraft photo courtesy U.S. Air Force by Staff Sgt. Bennie J. Davis.

Atmospheric Early Warning

The AEWS, conceived after World War II as a defensive shield for the United States and Canada against bomber attacks, comprises a number of radar sites in the continental United States, Canada, Alaska and Hawaii. As a component of the North American Aerospace Defense Command (NORAD), the AEWS integrated surveillance system effectively tracks every aircraft over the U.S. and approaching its borders. The system does not track objects in space, nor does it duplicate the routine radar coverage provided by civilian and military air traffic control systems. AEWS exists to track any aircraft that might be perceived as a threat and determine its course and probable destination.

While the threat from enemy military bombers has receded since the earliest days of the Cold War, the hijacked airliners that launched terror attacks on September 11, 2001, provided the Air Force new impetus to keep AEWS functional and strong. The AEWS is divided into six sectors, three of which cover the continental United States.

The AN/FYQ-93 system, which includes computers and peripheral equipment that receive and process tracking data from ground radar systems, is installed at AEWS Region/Sector Air Operations Centers. Although the AN/FYQ-93 computer system and display systems are near the end of their expected service life, they are being modified for improved reliability and maintainability. Because of SwRI's long background in providing support for aging military systems and its diverse work experience, it is especially capable of performing the task.

An SwRI engineer compares the operation of a redesigned AEWS console circuit board, left, with an original circuit board that it is intended to replace. Note the reduced number of components needed for the replacement board.

Scope of Work

SwRI engineers examined circuit boards from AEWS computers and attempted to determine their function through a documentation search. In many cases, neither the parts themselves nor the records or diagrams used to make them were available. In those cases, engineers were to identify the devices on a circuit card and determine their function, then determine how the various parts are connected together, and finally design new circuitry to replicate that function. Once engineers determined the function of the old card, they were to duplicate its design with equivalent components and diagram the replacement part.

Where possible, the replacement chips were to utilize programmable logic so that their function could be corrected or adjusted as necessary. However, some circuit cards, such as video cards, did not lend themselves to programmable logic and needed to be replaced with specially designed chips. During the replacement process, SwRI engineers added improvements such as enhanced signal and signal conditioning on the cards. Team members captured the old card's original design in a hardware design language that described the complete function of that card. Thus, if that function needed to be duplicated, it could be done using the latest devices.

Although new computer chips were used in a new design, they were placed on a circuit board that fit into the original slot occupied by the original equipment part. In many cases, a circuit board that originally contained many chips was replaced with a card that held only one chip plus a number of interfaces. In other cases, engineers provided an interface between the outside world, the original equipment and the new replacement part. Problems frequently had to be overcome, such as integrating modern logic operating at 1.7 volts with existing logic that uses 5 volts.

Finally, SwRI provided the new cards to the people who maintain the AEWS system and also provided the documentation needed to make sure that more cards could be manufactured if they are needed in the future.


Re-engineering electronic components for a robust, functional military system such as AEWS requires that engineers accommodate the design imperatives of military planners, who typically seek a system with a lifespan of at least 20 years, with the realities of an electronics industry in which the average turnover of component technology is about six months. That translates into the appearance of a new generation of equipment - faster, better, with lower power demand - twice each year. Maintaining such aging equipment calls for not just reverse engineering, but re-engineering the components, and not just duplicating the old equipment but duplicating its function in a newer, better, more robust platform.

Comments about this article? Contact McDaniel at (210) 522-6856 or

Published in the Spring 2004 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.

Spring 2004 Technology Today
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