Nondestructive inspection: Finding the cracks

Staff Sgt. David Bayle inspects an aircraft pin for cracks under a black light after dipping the part into chemicals mixed to show cracks not normally visible to the naked eye at the 379th Air Expeditionary Wing in Southwest Asia, Aug. 6, 2013. Bayle is a 379th Expeditionary Maintenance Squadron nondestructive inspection craftsman deployed from Eielson Air Force Base, Alaska, and hails from Port Sanilac, Mich. (U.S. Air Force photo/Senior Airman Benjamin Stratton)

Staff Sgt. David Bayle inspects an aircraft pin for cracks under a black light after dipping the part into chemicals mixed to show cracks not normally visible to the naked eye at the 379th Air Expeditionary Wing in Southwest Asia, Aug. 6, 2013. Bayle is a 379th Expeditionary Maintenance Squadron nondestructive inspection craftsman deployed from Eielson Air Force Base, Alaska, and hails from Port Sanilac, Mich. (U.S. Air Force photo/Senior Airman Benjamin Stratton)

SOUTHWEST ASIA -- While playing football during physical training, an Airman hurts his arm. Thinking nothing of it, he brushes it off and continues playing. Though after weeks of excruciating pain and a visit to the medical group's radiology section, an x-ray finds his ulna is fractured. Aircraft undergo similar stressors requiring specially trained Airmen to find the mechanical fractures.

Nondestructive inspection Airmen assigned to 379th Expeditionary Maintenance Squadron here specialize in finding fatal cracks in aircraft parts before they lead to catastrophic failure.

"We're an inspection branch and it's our job to make sure the aircraft are structurally sound," said Master Sgt. Steven McCabe, NDI NCO in charge deployed from Dyess Air Force Base, Texas, and hails from Irrigon, Ore.

NDI Airmen determine what test method to use and prepare fluids and parts for inspection. They also analyze worn metal content on engine-lubricating oil and other fluids, and recommend corrective actions. These Airmen are proficient in metals identification, detecting metal discontinuities and flaws, radiological safety and radiation monitoring.

"So in a nutshell, we find cracks you can't see with the naked eye and we have different processes to detect these cracks," said Staff Sgt. David Bayle, a 379th EMXS NDI craftsman deployed from Eielson Air Force Base, Alaska, and hails from Port Sanilac, Mich. "If we don't find the crack, the part itself could fail and it could be very detrimental to the aircraft and the support equipment used to maintain the aircraft."

Unlike other maintenance career fields, NDI Airmen must understand a fair amount of chemistry as well.

"I had no idea chemistry would be involved in a mechanical career field; my recruiter just told me I'd look for cracks," said Senior Airman Darnell McConnell, a 379th EMXS NDI journeyman deployed and hails from Colorado Springs, Colo. "NDI is like the coolest field out there and is essentially a non-fail mission. One of my favorite methods is the magnetic particle inspection."

MPI is a process for detecting surface and slightly subsurface discontinuities in ferromagnetic materials such as iron, nickel and cobalt. The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization. Direct current is passed through the part and a magnetic field is formed in the material. The presence of a surface or subsurface discontinuity or crack in the material allows the magnetic flux to leak thus proving the presence of an imperfection in the part.

"MPI is easy because the crack glows very bright," McConnell said.

But as with most maintenance Airmen, they're all about providing joint warfighters with the best machine possible as their work directly impacts the safety and security of aircrews down range.

"So if it's a wing, we're looking for a crack in the wing; if it's landing gear, we're looking for cracks in the landing gear," said McConnell. "If we don't find the crack, then eventually whatever it is, it's going to collapse and fail."

"It makes me feel really good that what we're doing not only saves the Air Force money, but also saves the Air Force lives," Bayle added.