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SwRI investigates crack in U.S. Air Force T-38 Talon fighter jet

The U.S. Air Force called on the Southwest Research Institute (SwRI) to help ensure fleet safety after a large crack was found unexpectedly near the cockpit of a T-38 Talon fighter jet. A new study describes how SwRI's risk and damage tolerance analyses helped determine a more effective inspection schedule, allowing the Air Force to find cracks before they grow to critical size.

Southwest Research Institute collaborated with the U.S. Air Force to ensure fleet safety when a large crack was found near the cockpit of a T-38 Talon. The Institute has been working to sustain the T-38, which was first introduced in 1961, for more than 40 years. [Credit: Photo courtesy of United States Air Force/Provided by SwRI]

 

 

 

 

SwRI has provided engineering support to the Air Force For several decades to extend the life of aircraft that have exceeded their original design life. The Institute has been working to sustain the T-38, first introduced in 1961, for more than 40 years. This activity includes using SwRI-developed models to predict crack growth to determine optimal inspection and maintenance schedules. The Air Force also uses finite element models to help predict the potential crack locations of the aircraft.

According to the U.S. Air Force, "The T-38 Talon is a twin-engine, high-altitude, supersonic jet trainer used in a variety of roles because of its design, economy of operations, ease of maintenance, high performance. and exceptional safety record." The aircraft has swept wings, a streamlined fuselage, and tricycle landing gear with a steerable nose wheel. The instructor and student sit in tandem under a glass cockpit fitted with integrated avionics displays, head-up display, and an electronic "no drop bomb" scoring system. Two independent hydraulic systems power the ailerons, rudder, and other flight control surfaces.

"Typically, our role involves predicting structural life and providing analysis used to help determine an inspection or repair schedule," said SwRI Lead Engineer Laura Hunt. "In the spring of 2017, when a large, unexpected crack was found by a crew chief in a longeron, a key structural component along the aircraft's fuselage, we were equipped for a rapid response."

This discovery resulted in the immediate grounding of the entire T-38 fleet for visual inspections, which were completed within four days. SwRI assisted with performing risk, damage tolerance, and failure analyses. A SwRI paper about the incident notes the fatigue cracks initiated from a fastener hole and "removal of a door provided the access necessary to the underside of the upper cockpit longeron."

While the crack appeared in a location that full-scale fatigue tests and finite element models did not predict, SwRI says it "responded swiftly, minimizing downtime and maintaining safety, resulting from the Institute's prior analysis work with the T-38 and other aging aircraft."

"A new problem was identified, and the entire team supporting the T-38 reacted quickly to ensure the safety of the T-38 and return it to service in a manner of days," said David Wieland, who oversees SwRI's Aerospace Structures Section.

Senior Research Engineer Mirella Vargas led the destructive failure analysis for the cracked T-38 longeron (a longitudinal structural component of an aircraft's fuselage). This entailed photographing the as-received component at the macro scale and examining specific areas with optical and electron microscopes at the micro scale, as well as identifying factors that contributed to the cracking. This analysis uncovered an additional crack in the longeron and determined that structural fatigue, the gradual weakening and eventual failure of a material due to cyclic stresses, caused both cracks.

"With this new information, we updated the model to improve the risk analyses," Vargas said. "Consequently, the frequency of inspections was adjusted, though not drastically changed. To maintain aircraft structural integrity, models may need periodic updates to ensure the safety and functionality of the aircraft components."

The updated inspection schedule ensured any risk remained low, balancing safety and efficiency until the remaining longerons could be replaced.

"This experience demonstrated our ability to quickly respond to unexpected issues," Hunt said. "It has reinforced the importance of being prepared and the need for robust analysis methods."

SwRI is a non-profit that has been providing independent, premier R&D services to government and industry clients since 1947.

The paper "T-38 failure analysis of an upper cockpit longeron for safety of flight and sustainment," appears in the Engineering Failure Analysis journal.

For more information about SwRI's capabilities in this area, visit the organization's Aircraft Structural Integrity Program (ASIP) page.

Source: Southwest Research Institute

Published March 2025

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