Researchers Seek to Find What Makes Inspectors Catch -- Or Miss -- Cracks In Airplanes

Release Date: July 2, 1998

BUFFALO, N.Y. -- Next to air-traffic-control issues or airline-security systems, tiny cracks in aircraft components are unlikely to provoke public concern.

But even though they rarely have the chance to grow large enough to cause a catastrophic plane crash (only two such incidents have occurred in recent aviation history), aviation experts know that that is two too many and that while rare, cracks that can become dangerous are amazingly difficult to detect.

In some cases, they go unnoticed even during inspections by veteran mechanics.

Now, University at Buffalo researchers are working on a Federal Aviation Administration-funded project designed to get visual crack-detection in airplanes down to a science.

The project consists of an analysis of data collected when the UB researchers and colleagues at Sandia National Laboratories asked 11 expert aircraft inspectors to find cracks on an out-of-service Boeing 737.

They systematically are exploring all of the elements that could cause one experienced inspector to find a crack and another one to miss it.

"The fundamental question we're asking is, why are some cracks found more often than others?" explained Colin Drury, Ph.D., professor of industrial engineering at UB and principal investigator.

Drury, a human factors expert who has spent his 30-year career studying -- and improving -- how people in the manufacturing and aerospace industries do their jobs, stressed that the project is unabashedly low-tech.

"While you need electronic tools to find very small cracks and those hidden under other components, the inspectors' eyes are still the main instrument we rely upon," he said.

However, visual inspection never has been examined in the same detail as some other methods, he added.

Drury noted that aviation inspectors are highly-skilled.

However, no body of recommendations currently exists that, when followed, predicts that most cracks will be found.

Drury explained that airlines want to target inspections to areas where cracks are hard to find but likely to cause problems.

Drury and colleagues at Sandia found that the experienced airline inspectors examining the Boeing 737 demonstrated a wide range of abilities in detecting cracks.

"Some of the cracks were found by all of the inspectors, but many others were not," said Drury.

While skill and years of experience were sometimes a factor in discovering some of the cracks, neither played a role in predicting detection in all of the cases.

"The more time you spend inspecting airplanes, the more you learn," said Drury. "But after a certain amount of experience, it's just not a factor in finding specific cracks."

"What we want to do is to find out where we should be putting our money in terms of improving crack detection," he said.

The team is using the results from the inspectors as a benchmark for exploring factors that contribute to detection.

To illustrate his point, Drury enumerated the mundane factors, which, if not optimum, could mean the difference between discovering a potentially dangerous crack and missing it.

"Lighting, of course, makes a difference, but we are trying to find out just how it makes a difference," he said.

The simple recommendation that a flashlight be positioned in several different places, rather than just one, could improve greatly the chances of finding a crack.

Accessibility to areas on the plane also is a factor.

"What position do you have to be in in order to find that crack?" asked Drury. "Do you have to be lying on your back or your side? Do you have to use an inspection mirror? If we know what affects visibility, then we know exactly what affects the inspection and how often to inspect."

The team has characterized 60 cracks all over the fuselage of the 737, photographing each, making measurements from the photos and evaluating each crack's accessibility and visibility.

By making a connection between characteristics of individual cracks and the level of difficulty with which they were found -- or not found -- by inspectors, the UB team will help engineers develop recommendations on the frequency of inspections for specific aircraft components.

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