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Aging Warplane, New Life

Upgraded weapons, electronics keep the A-10 Thunderbolt II a winning combat aircraft

The A-10, in the U.S. Air Force inventory since the 1970s, remains a front-line aircraft for close-air support.

By Christopher E. Camargo

U.S. ground combat troops fighting in Southeast Asia in the 1960s and Ô70s were supported from above by a slow, low-flying, heavily armed airplane that had been built for war in an earlier era. The piston-engine, propeller-driven Douglas A-1 Skyraider was designed as a World War II dive bomber but stayed in service for nearly three decades after being adapted for a ground-attack role. Although it could drop ordnance more accurately, absorb more damage and stay over the target longer than the fast-flying, fuel-gulping jets of the Vietnam War, the A-1’s service life ended as the military upgraded to all-turbine aircraft.

Its successor, the straight-wing, subsonic, twin-jet A-10 Thunderbolt II, was designed specifically with close-air support in mind. Introduced in the mid-1970s, the A-10 was equipped with free-falling bombs, missiles and a cannon that could destroy armored vehicles and tanks during low-level attacks.

Three decades later, today’s air combat arena is dominated by high-technology cruise missiles, unmanned aircraft and stealthy, fly-by-wire jets carrying precision weapons. Still, armed with new electronics and new precision weapons, the rugged and adaptable A-10 has defied obsolescence by excelling in close support of ground troops in Iraq and Afghanistan.

Like the A-1, the A-10A earned ground troops’ respect for its low-and-slow attacks, long loiter time and heavy armament. Those unique characteristics, plus the addition of modernized weapons-control, communications and navigation electronics, culminated in a new, precision-engagement-capable A-10C version that reached service in 2007. With those improvements, plus updated wings and possibly engines to increase performance, the A-10 is projected to remain in the U.S. Air Force fleet until at least 2028.

Close-air support

The A-10, manufactured by Fairchild-Republic Inc., was built for the rigors of low-altitude combat. Its forward fuselage was essentially built around a GAU-8A Avenger 30-millimeter, seven-barrel Gatling gun. Carrying cluster bombs and Maverick missiles under its long, straight wings, the A-10 was made for combat survivability and maneuverability in lieu of speed. Its single pilot is protected from ground fire by an armored cockpit. Twin rudders shield the engine exhaust from infrared heat-seeking missiles, a rugged landing gear allows operation from forward landing strips, and redundant control systems are designed to get the plane safely home despite battle damage.

Its analog controls, weapons systems, electronics and avionics were kept simple for ease of maintenance. However, that same simplicity turned into disadvantage as it limited the integration of more sophisticated navigation technology, such as global positioning systems, and precision-weapons technology as they became available in later years. Bringing a 1970s-vintage airplane into the digital, precision-weapons age created unique engineering challenges.

Christopher E. Camargo is director of SwRI’s Avionics and Support Systems Department within the Aerospace Electronics and Information Technology Division. He is responsible for A-10 Systems initiatives conducted at the Institute, including technical and management oversight of ongoing development programs. He has served as lead engineer on a number of other programs involving both manned and unmanned aircraft, and leads internally funded, multidivisional research initiatives in the areas of software defined radios, autonomous unmanned ground vehicles and A-10 aerodynamic and ballistic modeling.

SwRI and the A-10

Engineers from Southwest Research Institute (SwRI) have been supporting the A-10 fleet since 1989 with design engineering modifications and upgrades designed to keep the vintage aircraft flying longer. The SwRI team initially supplied legacy weapon system support, system engineering, modifications and upgrades, electronic hardware design engineering, embedded applications software development and test and diagnostics development for the Sacramento Air Logistics Center. As part of that work, SwRI engineers inserted new technologies to complement or replace legacy systems for engine monitoring and data recording. They also have added improved support equipment and new technology for enhanced targeting, advanced navigation and better pilot situational awareness.

A-10 Prime Team

In 1997, with the airplane’s original manufacturer no longer in business, the U.S. Air Force awarded a contract to care for the A-10 fleet to a ÒPrime Team,Ó led by Lockheed Martin Systems Integration in Owego, NY. The team also comprised SwRI, BAE Systems and Northrop Grumman. Programs undertaken by the A-10 prime team have addressed large-scale systems, weapon systems, support equipment, structural engineering, maintenance and support, and aircraft trade studies.

The SwRI engineering team supported Lockheed Martin in bringing the A-10 into the world of network-centric warfare (NCW), which increases combat capability by tying together sensors, pilots, ground personnel and combat decision-makers. When networked in this way, warfighters can share combat awareness, increase the speed of command and maintain higher-tempo, synchronized operations for greater effectiveness and survivability.

SwRI avionics technicians retrofitted the new A-10C with a situational awareness data link (SADL) radio as an integral portion of NCW, providing the communications and networking capability for mobile forces that, together with the global information grid and communication satellites, enables robust enterprise-wide networking. The SADL provides communications and data transfer among combat aircraft, reconnaissance aircraft, ground vehicles and troops to share information about fighter status, targeting data and the positions of friendly troops.

Adding the SADL radio made possible greatly improved interoperability between the A-10C pilot and air and ground forces. The data link connects the A-10 to the “digital battlefield,” increases the pilot’s situational awareness to better avoid fratricide in combat situations, and enables field commanders to direct attacks on specific targets. SwRI engineers, in coordination with LMSI, also continued development of a modification kit to replace current aircraft identification systems with new transponders required for operating in European airspace.

In addition, SwRI engineers supported Lockheed Martin for the precision-engagement updates for the A-10C version by integrating advanced smart bombs into the weapons system. They also updated targeting and weapons release capability, enhancing the A-10 cockpit and providing updated flightline support equipment.

Other upgrades to the aging aircraft have included an improved pilot’s head-up display that uses multifunction color displays to add greater functionality for future growth and to show flight and weapons delivery information using standard symbology, and other cockpit enhancements to allow A-10C pilots to operate weapons and communications systems in combat while keeping their hands on the throttle and control stick.

SwRI developed an operational-level tester to troubleshoot and diagnose problems with integrated avionics and weapons systems, subsystems and sensors for the A-10A and the upgraded A-10C aircraft.

SwRI engineers also performed upgrades to facilitate A-10 flightline maintenance. These included a tester to provide troubleshooting and diagnostic capabilities for maintenance on the integrated avionics and weapons systems, subsystems and sensors for both the A-10A and the new A-10C aircraft. The tester comprises a portable automated test station and operational test program software to verify the status of weapon stations using discrete data acquisition as well as through the airplane’s avionics bus. Meanwhile, using SwRI internal research funding they also developed a ruggedized, lightweight, hand-held device that acts as a remote terminal to download engine data used by the A-10 engine structural integrity program via the avionics bus. The mobile device enhances efficiency on the flightline while reducing the amount of support equipment needed.

An SwRI team went to Nellis Air Force Base, Nevada, for on-site support of flight test operations as part of the A-10C precision engagement program. There, they assisted with aircraft maintenance and post-mission pilot briefings and also provided training for Air Force maintenance crews.

Following flight testing, SwRI engineers also accompanied the A-10C crews to combat theaters in Afghanistan and Iraq, where the aircraft has proved to be highly successful in delivering smart weapons reliably and on-target.

In October, 2007, the A-10 Precision Engagement Program won the Department of Defense and National Defense Industrial Association’s 2006 Top 5 DoD Program award for excellence in systems engineering.

Besides enhancing the operational usefulness of the A-10, SwRI engineers addressed the structural integrity of the airframe as part of a multidisciplinary approach to help the military evaluate and extend the life of aging military systems. Because upgrades to extend service life by reinforcing wing components, expanding precision-weapons capabilities and improving communication data links all have implications for the airframe itself, the A-10 Prime Team is revitalizing the aircraft structural integrity program to sustain the aircraft as its flying hours increase and its usage expands.

Future programs

A number of additional programs are planned to keep the A-10 a viable combat system through at least 2028. The Prime Team is investigating further upgrades to the pilot’s communication, navigation, surveillance and air traffic management capabilities. In addition, upgrades are planned for the Joint Tactical Radio System as well as avionics hardware and software. Further integration of a powerplant upgrade program and flight-test support, plus future aircraft structural integrity program support, are also planned.

Questions about this article? Contact Camargo at (210) 522-2095 or

Ballistic Scoring - Improving the A-10’s accuracy with unguided weapons
By Christopher J. Guerra

When engineers for SwRI’s Avionics and Support Systems Department learned in 2005 that in some undefined circumstances the A-10 was delivering unguided munitions significantly beyond the intended target, they designed an internally funded research project to address the problem. The result was a multi-year, multi-division approach to developing the modeling and simulation tools necessary to score, or evaluate, the ballistic performance of the plane’s weapon delivery process.

The analysis required access to flight range data, where military personnel evaluate aircraft for a variety of applications. The military agreed to share the data with SwRI for this project.

Christopher J. Guerra is a research engineer in the Integrated Diagnostics Section of the Avionics and Support Systems Department. His primary interests are in autonomous systems, control, and modeling and simulation of dynamic systems.

The A-10, like other modern aircraft, has many embedded computers performing a variety of functions. One computer manages data that the pilot loads prior to takeoff, while others generate the imagery and symbology on the various cockpit displays. In this case, the SwRI team was interested primarily in data from the Low Altitude Safety and Targeting Enhancements (LASTE) system, for which the main computer is the Integrated Flight and Fire Control Computer (IFFCC). The LASTE stabilizes the aircraft for precise delivery of weapons during the specialized missions of the A-10. As the close-air support weapon of choice, the A-10 flies low and slow. This exposes the aircraft to threats at very close range for longer durations than many other fixed-wing aircraft. As the primary computer in the LASTE, the IFFCC performs a number of significant functions. The first function is state estimation, which is a process to estimate the aircraft’s position, attitude and velocity from sensor data. Second, the IFFCC generates the image seen through the pilot’s head-up display (HUD). Third, the IFFCC computes the weapon’s trajectory and determines its release time, or it aids the pilot in selecting a release time.

The test aircraft at the flight range have accurate positioning instrumentation to assist evaluation of the aircraft performance. In addition, many of the aircraft’s computers are connected via a network or avionics bus compliant to MIL-STD-1553. Colleagues in the military shared the bus data and test range data for a large set of missions. Armed with this information, the SwRI team could proceed with developing the modeling and simulation tools.

The first step was to develop software to parse the data files. Unlike standard file formats, the files that the SwRI engineers needed are often split into multiple sections comprising hundreds of megabytes per mission. In parallel with this effort, other engineers from SwRI’s Mechanical and Materials Engineering Division applied their experience in ballistics to develop a computational model of the ballistic trajectory of weapons such as unguided bombs, gun rounds and rockets. The staff then validated this model to the U.S. Air Force SEEK EAGLE model, which is considered a standard.

Using internal research funds, SwRI engineers apply model-based design techniques to develop ballistic models, design weapon scoring algorithms and test real-time software to help resolve challenges related to the accurate delivery of non-guided, free-fall ordnance and provide alternative solutions for flight testing and algorithm analyses.

The team received further support from experts in statistics from SwRI’s Fuels and Lubricants Research Division. A sensitivity analysis of the model indicated those parameters that could significantly affect performance.

All of the preceding activities were essential to building the scoring capability. “Scoring” in this effort meant evaluating software upgrades to the IFFCC to evaluate their performance. This research defined scoring to include a variety of values. These included impact point vs. target position, or the difference in the downrange and cross-range directions between the two points; the method of test, or the procedures the Air Force uses to evaluate performance; and ballistic error decomposition (BED), which decomposes the contributions of various factors that can contribute error to the process.

BED is what makes SwRI’s approach unique. As a result of this internally funded research project, the SwRI team recently performed funded work that included analyzing source code for the premier A-10 flight training model. The SwRI team made recommendations to upgrade scoring capability in the laboratory. Since that meeting in February, the A-10 Prime Team has briefed SwRI’s capability in this area to the commander of Air Combat Command, which manages the A-10 weapon system.

The future of ballistic scoring at SwRI has significant potential. Several clients are looking for expertise in this area, and SwRI is positioned to leverage this technology to support the military.

Questions about this article? Contact Guerra at (210) 522-3481 or

Published in the Spring 2008 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.

Spring 2008 Technology Today
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