Fear of the unknown, nothing to fear at all

  • Published
  • By Senior Airman Mark Hybers
  • 507th Air Refueling Wing, Public Affairs
TINKER AIR FORCE BASE, Okla. --  Most people associate fear of the unknown with something negative, but for one shop within the 507th Maintenance Squadron, the unknown is what makes it an integral part of the mission.

In this case, the unknown is cracks in metal or sheet metal parts off the KC-135 Stratotankers and it's exactly what members of the non-destructive inspection (NDI) lab look for when they come to work.

Each morning Tech. Sgt. Steven Smith, NDI shop chief pulls up a computer program called G081 to see what requests have been submitted. Most requests are submitted from the sheet metal shop and can be anything from a bolt off a wheel to testing one of the wings.

The process for testing cracks is not an easy one but it is a critical piece to the overall inspection and maintenance mission.

"NDI plays a big role in the readiness of the aircraft," said Senior Master Sgt. Larry Spradling, 507th fabrication flight chief. "The inspections they perform show defects that are not detectable by the human eye. It's a very important part of the process."

There are five tests performed by the NDI shop: The penetrant test, magnetic particle test, ultrasonic test, eddy current test and the x-ray test. Smith matches the information in G081 to a technical order (TO) to perform the correct test.

"The TO breaks down everything you need to know about the inspection - which of the five tests to perform, details about the part or parts being tested, calibration settings and much more," said Smith.

Many of these inspections are time consuming and require a great deal of preparation before the inspection actually happens.

Take for instance, the penetrant test. Once cleared of oils and dirt, the part is dipped into a penetrant solution and then sits to dwell (set up) for a period of time. Dwell times vary depending on the part. Once the penetrant soaks into the part it's rinsed off with water. From there the part is rinsed with an emulsifier, which is a soap-like substance. The part is rinsed off with clean water and then dipped into a developer for about a minute before making its way into a large drying machine. From there, it's off to an enclosed area to be inspected under a black light.

Cracks appear as a green line under black light testing.

Not all parts are easily removed from the aircraft for testing, however. For these parts the NDI lab is equipped with portable equipment. The mobility comes in very handy especially during an Isochronal Inspection (ISO). The ISO is an in depth inspection that tests an aircraft from top to bottom, inside and out.

"The NDI guys are able to come out to the aircraft during an ISO and perform bulkhead tests," said Master Sgt. Jason Lawson, 507th ARR shop chief. "They perform inspections on all of our hardware, on or off the plane. They really do a lot for us," he said.

All-in-all, this team of five performs roughly 300 inspections per month. Whether it's a bolt off a wheel or an x-ray on the wing, every inspection is handled with precision down to the thousands of an inch.

"We take this stuff very seriously," Smith said. "If we miss something, it could be catastrophic."

So, don't be afraid of the unknown - at least not when it comes to cracks on a KC-135 that aren't visible to the human eye. There's a little known crew in a lab testing for it right now.