Nondestructive inspection team strives to increase reliability

Published Nov. 14, 2007
By Kandis West
72nd Air Base Wing Public Affairs

TINKER AIR FORCE BASE, Okla. -- Many have heard the saying "If you step on a crack, break your mother's back."

Well, if aircraft inspectors miss a tiny crack in an engine or a critical component on an aircraft, the Air Force bird could fall out of the sky.

The Air Force Nondestructive Inspection team ensures aircraft inspectors use the right tools and processes to catch the smallest cracks in order the keep aircraft in the sky.

"It's not the smallest flaw you can find, it is the largest one you may miss that's important," said Karl Kraft, Air Force NDI program office lead engineer.

The nine-member office is headed by the Air Force Research Laboratory and supports all field labs, including labs for the 190 active-duty, Air National Guard and Reserve bases worldwide.

"Anywhere there is aircraft flying, there will be an NDI presence," said Michael Paulk, chief of the Air Force NDI office.

The NDI team is testing new equipment and improving inspection processes to increase the reliability of field inspections and the probability of finding smaller flaws on aircraft critical components.

The first step was a $1 million grant to take the mechanical probes used on the automated Retirement for Cause eddy current systems at the Oklahoma City Air Logistics Center here and use them for manual inspections on aircraft parts in the field and at depot maintenance repair facilities.

Mr. Kraft said throughout the aerospace industry, a traditional manual eddy current inspection (a process used to find small cracks invisible to the human eye) is roughly capable of finding a 0.1-inch crack as opposed to the OC-ALC's engine inspection shop that can find cracks a tenth of that size with the automated systems.

"One key performance parameter of this program is to cut the current probability of detection size of surface eddy current inspections in half Air Force wide," Mr. Kraft said. "If we can reliably detect smaller flaws, then maintenance intervals may be extended, increasing aircraft availability to the warfighter."

The manual probe is similar to a pencil tip and very susceptible to titling that would reduce sensitivity. The new mechanical probes contain a specially-designed coil that conforms to the surface and allows less degree of movement, increasing the probability of finding a smaller crack.

"This type of equipment will be used to reduce human factors that adversely affect inspector performance," Mr. Kraft said.

Another human variable affecting performance is the type of training an inspector has received, Mr. Kraft said. The NDI program office wants to create a new NDI Reliability System that will standardize training throughout the Air Force.

The team has been performing probability of detection, or POD, studies for the past three years to measure the reliability of surface eddy current inspections in the field to identify shortcomings in inspection capability.

"The data is pointing toward the training," said Mr. Paulk. "Typically inspectors trained at the Air Force NDI school did better in the POD studies that those only receiving training locally."

The team is supporting the air logistics centers on a training plan to overcome gaps between requirements and capability. The team is developing a standard training program where half of the training will be completed in the classroom. The other half will involve hands-on training. Tinker AFB is the lead in this effort, Mr. Paulk said.

The NDI team is also working on acquiring non-contact scanning equipment that would allow for inspections without the probe contacting the surface of the part. A proposed scanner would allow a single device to scan aircraft skin surrounding a fastener without having to change probes to accommodate different fastener sizes. The proposed device would work for both raised and flushed fasteners.