Diagnosing Aerospace Maladies

Non-Destructive Testing (NDT) and inspection (NDI) equipment is used throughout the manufacturing process for aerospace components as well as in the case of catastrophic failure analysis. Technologies such as remote visual inspection, eddy current, x-ray and ultrasound are used to examine materials and components to ensure quality and safety in aircraft.

These technologies are not new; even before aerospace applications, they have been used in the medical field for years. Remote visual inspection evolved from medical endoscopy, eddy current is the equivalent of MRI equipment, and x-ray and ultrasound are staples in medical diagnosis. Now, the procedures have been adapted to industrial - specifically aerospace - applications, in an effort to keep aircraft healthy and maintain the safety of the people inside.

From the Hospital to the Shop Floor

Diagnosing a problem - either in a human or in industrial equipment - takes advanced imaging tools, which differ in methods and are more advantageous in certain circumstances over others.

MRI » Eddy Current

MRI (Magnetic Resonance Imaging) machines use magnetic fields to create images and enable doctors to visualize the internal configuration and function of the body. In the aerospace industry, eddy current is used for the same application on an aircraft component or material.

Typically, eddy current is used for detecting cracks in aluminum components that an inspector can not see unaided. In typical failure analysis tests, parts are destroyed and cross-sectioned to look for defects. Using eddy current, this is no longer necessary, allowing the parts to be kept whole and only defective portions removed.

Inspectors induce a magnetic field into aluminum, because the metal is conductive.

"We induce the magnetic field and then we measure the response to that," says Jeff Anderson, GM of Inspection, GE Sensing & Inspection Technologies. "If there's a crack, you see a difference in the magnetic properties of that material."

Endoscopes » Remote Visual Inspection

When a patient undergoes an endoscopic exam, a tube with a camera on the end, called an endoscope or a borescope, is inserted into the body to assess the interior surface of an organ. Typically, the camera is able to record both video surveillance and take still pictures. The same technology that is used in aerospace applications is called remote visual inspection. The main application for remote visual inspection is the examination of engines.

"Engines are designed with boroscopic ports, where you can insert the borescopes and look at the turbine blades in an engine to make sure that they're still in good shape," Anderson explains.

Other circumstances that are ideal for using remote visual inspection are when confined spaces in the airframe, such as cockpits, internal portions of the outer skin, or fuel tanks need inspected. This type of technology is another way to view parts or structures while keeping them intact, even though they may be in places where humans are unable to operate.

X-Ray

When people suspect they have a broken bone, they go to the hospital to have it xrayed.

X-rays are radiographic images that show a clear distinction where there is a crack or lack of material. The same goes for aircraft components such as turbine blades.

Ultrasound

Ultrasound imaging in medical applications is also called sonography. This medical imaging technique uses sound waves out of the realm of human hearing to penetrate the body and measure the reflective signature of an organ, tendon, or muscle in the body. The doctors are able to determine if there is an irregularity based on the images produced by the reflective signatures. In the aerospace industry, this technology is best used for inspecting composite materials for delamination or defects.

"Composites are made with a layering technique, and bonding or disbonding of those layers when they're made is the key to integrity in the part," Anderson says. "The best way to inspect for that in an economical means is ultrasound. It shows up very rapidly if there are disbonds."

Failure Analysis

After an aircraft suffers a catastrophic failure, possibly causing a crash, investigation crews must do thorough examinations to determine what caused the crash, and whether improvements to certain parts or materials could prevent future incidents. Inspection techniques used during the manufacturing process are also used for post-catastrophic failure analysis. When possible, it is important to keep from further damaging an already unstable or fragile part during inspection.

For this reason, non-destructive testing is highly beneficial.

"With the remote visual borescopes, without taking apart the engine, you can actually go in and take a look at things that you may disturb or damage when you take it apart," Anderson explains. "The ability to do that either for sections of the aircraft or the engine specifically, portions that may be damaged, is a pretty big opportunity." X-ray is used for the same types of processes.

An inspector is able to x-ray portions of an engine or a structure to assess the damage.

The biggest use of x-ray technology is in the inspection of turbine blades.

The blades are made from wax castings, and extensive x-ray inspection is performed throughout the manufacturing process.

When a blade is inspected post-incident, x-ray is often used again to compare to the previous x-rays and determine if a blade is damaged.

Ultrasound is another great tool from a failure analysis standpoint. A person may be able to see damage visually from the outside, but further damage or delamination can actually be much worse on the interior layers or in another area. Ultrasound helps to track those defects that can't be seen.

Ultrasound is especially advantageous when inspecting composite military planes that have been damaged from bullets, birds, other aircraft or other projectiles. To repair the aircraft, one must know how much needs to be cut out of the plane, or if it is salvageable at all. Ultrasound technology gives the inspector a means to see inside and assess the damage.

"Ultrasound is used as mitigation means for the aircraft that may be in service to have them go and be inspected," Anderson explains. "That's a huge outcome if there is an incident in the industry where there's a component failure, even if there was no accident.

These methods are used routinely - daily - to do inspections on aircraft that are in service." Anderson says that 90% of the time a structural component causes a problem with an aircraft, the remediation for the aircraft that are still in service is ultrasound inspection, in order to prevent future failure.

To determine which method of inspection is appropriate for a situation, a team of application specialists determine on a caseby- case basis which operation would work best. "If someone comes to us and says we have a component or structure to inspect, we would triage that - just like if you go to a hospital," Anderson says.

Sometimes, a number of different inspections are performed on a component and the best result is used from those for the rest of the parts or for future incidents. Ultrasound and remote visual inspection are the biggest in-service inspection tools, with the remote visual inspection being the biggest.

Engines are routinely examined with remote visual inspection.

When there is a catastrophic failure that has been deemed to be a component or manufacturing issue from a materials standpoint, the inspection criteria becomes much more stringent. This, in turn, makes the structure or component safer for people in the future.

"As a result of every one of those incidents, the inspection pieces typically revolve around more non-destructive testing during manufacture and/or more inspection during in-service," Anderson says. Postcatastrophic failure analysis is often used for the basis of re-design, when necessary.

Current and Future Challenges

"The challenge is making sure that we're applying the best technology that we can to the whole safety issue," Anderson says.

Inspecting aerospace components and ensuring safe assemblies translates to saving lives. Failing to do so may result in injury or death.

Typically, the aviation industry is about 10 years behind the technological evolution of the healthcare industry. In the future, the kinds of tools used for minimally invasive diagnosis and inspection for human bodies will continue to be adapted for industrial purposes, allowing manufacturers, MRO professionals, and inspectors to conduct critical examinations of parts and structures without causing unnecessary damage.

GE Sensing and Inspection Technologies
Billerica, MA
gesensinginspection.com