NDT Applications: Borescopes Used in Aircraft Engine Inspection
Borescopes are easy-to-use optical diagnosis instruments that view, magnify and illuminate hard-to-reach areas. They can be extremely valuable tools for detecting problems in general aircraft engines.
Gary Seabert, president of Island Aviation Service (Fernandina Beach, FL) found that out when his FBO hosted a recent service clinic for the American Bonanza Society/Air Safety Foundation (ABS/ASF).
Teledyne Continental Motors (TCM, Mobile, AL), a manufacturer of aviation supplies, sent two field engineers, an accident investigator and a field supervisor to the clinic as part of an ongoing effort to improve customer service. This team used two battery-powered portable bore-scopes to inspect TCM engines.
"We used the scopes ourselves as part of the inspection, and spotted defects in the walls of a new cylinder that had only 15 hours of service," says Seabert, who is an Airline Transport Rated rated pilot and an authorized aircraft inspector.
Seabert says the walls were shedding microscopic pieces of metal that eventually would have gotten into the oil and contaminated it. This could have seriously damaged the bearings on the Bonanza engine.
"If we hadn't caught the problem in that inspection, we wouldn't have known about it until the metal showed up in the oil filter in the next 50-hour oil change," Seabert says. "In that time, the metal could have caused a lot of damage."
The borescopes also showed that cylinders on another engine, which Seabert says he thought might have some problems, were perfect. "So we got some good news and some bad news," he adds. "Essentially, it all amounted to the same thing-the scopes allowed us to provide good information to customers and save them money."
After the clinic, Seabert ordered a scope similar to TCM's from the manufacturer, Lenox Instrument Co. Inc. (Trevose, PA). Originally developed for inspecting automobile engines, the portable borescope, which weighs only a few pounds, is called the Autoscope.
"All of our engine inspections are now borescoped. Any time we remove the spark plugs for engine work, we take a few extra minutes to look at the cylinder walls and valves," Seabert says. "If we're doing a compression check, for instance, on a 50-hour, 100-hour or annual inspection, we'll always view the walls with the scope. And we will certainly scope the engine if a pilot has an oil consumption problem or other specific problem with an engine."
The Autoscope includes a nine-inch-long stainless steel probe that fits into any opening larger than 5⁄16 inch, including spark plug holes. The scope magnifies 3X through an optical lens system and illuminates though a high-intensity quartz halogen light source at its tip. A stainless steel battery pack, which serves as a handle during inspections, holds three standard "C" batteries.
Rigid borescopes like the Autoscope are used where a straight line path is available between the maintenance inspector and the area to be viewed. Flexible fiber optic scopes, on the other hand, are snaked through engines when obstructions and curves don't allow a straight path. In these, thousands of individual glass fibers carry light to the point of inspection and also convey the image back to the viewer's eyepiece.
"It's important to get a scope that gives you the results you need," Seabert says. "I previously used several other, much more expensive, scopes, but I could never see anything, no matter how I squinted or repositioned it," he says. "I didn't use them much. We found the right scope, which allows us to really view the valves and cylinder walls with great clarity. The people in our maintenance shop love the scope."
Lenox Instrument Co.
Sidebars:BenefitsA borescope was used on an engine with only 15 hours of service and it spotted defects in the walls of a new cylinder.
The walls were shedding microscopic pieces of metal that eventually would have gotten into the oil and contaminated it. The problem would not have been caught its next 50-hour oil change.
The borescopes also showed that cylinders on another engine thought to have defects was defect free.
Decreased inspection time.
The ability to extract accurate results. Archiving of data is possible.
Limited training is required leading to immediate productivity gains.