NDI stops problems before they start

  • Published
  • By Capt. Eric Badger
  • 379th Air Expeditionary Wing Public Affairs
SOUTHWEST ASIA (AFPN) --  Similar to a private investigator gathering evidence to crack a case, the Non-Destructive Inspection unit here also gathers evidence -- but its intent is to ensure the case remians uncracked. 

The NDI unit uses methods such as magnetic particle, fluorescent penetrant, X-rays, and eddy current to detect cracks and pits in aircraft parts to prevent aircraft malfunctions. And their performance appears flawless.

“The Non-Destructive Inspection shop here is better than most NDI shops at stateside bases,” said Lt. Col. Don Atkinson, commander for the 379th Expeditionary Maintenance Squadron. “There’s very little they can’t do.” 

If a crack or defect is detected in a mechanical part, NDI sends it to the maintenance structural repair unit for repair. 

“We do preventive maintenance checks on virtually any aircraft part from nose wheels to bolts,” said Master Sgt. Michael Johnson, an NDI technician deployed from Peterson Air Force Base, Colo. “Also, if the maintainers on the flightline detect a problem or think there is an issue with a part, they let us know and we’re on the job.” 

The NDI shop identifies part defects by two common methods -- magnetic particle and fluorescent penetrant. 

The unit’s magnetic particle method is used for detecting defects in ferrous parts such as steel. In this process, the part is magnetized by using an electrical current that creates a magnetic field through the part. Cracked areas create north and south poles on either side of a defective area. When magnetic particles are applied to the part, the poles attract the particles and an indication of the crack is formed. 

The fluorescent penetrant method detects cracks and pits in parts made of nonporous materials such as aluminum, titanium and magnesium. This process depends on the ability of the penetrant to enter into a surface defect. 

Both methods rely on fluorescent chemicals and ultraviolet lighting to reveal defects, Sergeant Johnson said. 

X-ray inspection uses the penetrating abilities of electromagnetic radiation to examine the interior of objects. 

Three prime factors determine the amount of information that X-ray can provide: composition of the object,  the product of the density and thickness of the material making up the object and the energy of the X-ray incident upon the object. 

Defects within the object can cause changes in the first two factors, allowing the defect to become detectable. 

The shop comes equipped with a dark room where X-ray photos are developed.
According to Master Sgt. Michael Winslow, an NDI technician deployed from Cannon AFB, N.M., ultrasonic testing is used to detect internal defects on most mechanical parts. 

“Much like a pregnancy ultrasound, the ultrasonic testing can locate small defects deep into the structure,” he said. “Ultrasonic testing uses a piezoelectric transducer to convert electrical signals to ultrasonic (mechanical) vibrations.” 

Eddy current uses a probe to an shoot electric current into a part to identify problem areas, said Senior Airman Antwon Gallagher, an NDI journeyman deployed from Grand Forks AFB, N.D. 

“When eddy currents encounter a defect, the surrounding currents become distorted, giving you a clear indicator that there’s a problem,” he said. “This change is detected on a meter or other type of display.” 

The NDI unit also analyzes oil samples as part of the Joint Oil Analysis Program to inspect for aircraft engine failure before it happens. 

The presence of unusual element concentrations in oil can indicate abnormal engine wear. Once abnormal wear is verified, the engine can be repaired or removed from service before a major failure occurs. 

NDI’s primary objective is to enhance safety and material readiness at a minimum cost, while serving as a decisive, preventive maintenance tool, Sergeant Winslow said. 

“We save lives and aircraft everyday,” he said. “Even if we don’t find any problems, the inspection pays for itself.”