U.S. Central Command, the military arm managing Operation Epic
Fury, reported on Monday that more than 6,500 combat sorties have been flown,
striking more than 7,000 targets.
The operation is being carried out by bombers, fighter jets,
helicopters, attack jets, electronic warfare aircraft, reconnaissance aircraft,
communications aircraft, and refueling aircraft. Some of these aircraft are approaching
69 years old. One refueling tanker, registration number 57-1419, built in 1957,
remains in service with the Arizona Air National Guard.
The Air Force’s Aircraft Structural Integrity Program (ASIP)
and the U.S. Air Force Academy Center for Aircraft Structural Life Extension
(CAStLE) ensure that aging military aircraft can continue to fly safely. These
programs use damage tolerance analysis, aircraft usage data, and the results of
nondestructive inspections to establish regular inspection intervals to extend
the life of aging structures.
Inspection Methods
On Monday, the Southwest Research Institute (SwRI), located
in San Antonio, Texas, announced that it has received a contract from the U.S.
Air Force Academy to characterize inspection methods for bolt holes in aging
aircraft, including inspections through bushings without removing them. SwRI
has supported ASIP and CASTtLE for decades. Assessing bolt-hole condition
through inspection supports broader efforts to inform repair decisions and
ensure aircraft safety.
“It’s important to inspect locations where stress can lead
to damage,” said SwRI Senior Research Engineer Nathan Richter, who oversees the
project. “We use nondestructive evaluation (NDE) methods in areas where cracks
may form. NDE helps detect damage without altering or removing a part, but its
sensitivity varies with the flaw size.”
Bolt holes require careful monitoring because they exist in high-stress areas
of the aircraft. When cracks or wear develop around a bolt hole, the damaged
material is often replaced with a cylindrical metal sleeve called a bushing.
“Inspecting bushing-repaired holes is challenging because the bushing must be
removed, risking further damage to the hole during removal and reinstallation,”
Richter said.
Inspect Air Force Repairs
To address this, SwRI is using low-frequency eddy current testing, an NDE
technique that applies electromagnetic fields to detect and characterize
subsurface flaws and cracks; using low frequencies allows the inspection to
detect flaws without removing the bushing. The method will allow the inspector
to more easily inspect Air Force repairs. Its performance to flaws of different
sizes is characterized by inspecting coupons with purposefully generated flaws
produced by SwRI. These results will then be used to develop probability-of-detection curves to characterize the method's flaw-detection capability.
Characterizing the performance of these methods will give aircraft maintainers
the confidence to assess damage progression and make repair decisions that keep
the aircraft flying safely.
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