A1C Tye Braden, a nondestructive inspection journeyman with 19 MXS, Little Rock AFB, Ark., calibrates an ultrasonic device that sends out sound waves. When the waves are bounced back at a certain frequency, NDI Airmen know they’ve found a crack. USAF photo by A1C Rhett Isbell
By MS. RITA HESS, Staff Writer
On April 17 this year, an engine on a Southwest Airlines flight broke apart, ultimately killing a woman in a window seat and causing sudden cabin depressurization. An inspection on the Boeing 737 just two days earlier revealed no problems with the plane or its engines. But finding flaws is not always easy.
Metal fatigue, for example, is sometimes invisible. It can occur due to issues like stress or vibration on older aircraft—or even on new planes if it is a hidden manufacturing defect. Indeed, a tiny crack that you cannot see might turn catastrophic within seconds and bring down an airliner.
The National Transportation Safety Board (NTSB) indicated early on that in the April fatality incident, a blade in the engine broke in two places: (1) where it attaches to the main hub and (2) higher up—about midpoint of the blade. It is unlikely that a routine visual inspection would have found it.
Earlier this year, in February, a United Airlines plane using a different engine experienced a similar issue that resulted in no injuries and only minor damage. Earlier still—in 2016—a fan blade separated and debris ripped a 16-inch-long hole in the fuselage of yet another Southwest Airlines plane, after which the engine manufacturer recommended that airlines should conduct scheduled ultrasound inspections of the blades.
So what does Air Mobility Command do to proactively spot metal weakness or tiny cracks that cannot be seen in a visual inspection ?
To fully understand this process, let’s think of a potentially catastrophic aircraft defect like we think of human disease. Even the best physicians (maintenance personnel) can have difficulty diagnosing cancer (the potential issue) in a patient (a plane) simply by looking with the naked eye. So a physician who suspects cancer might order an X-ray.
Airmen from the 19th Maintenance Squadron Nondestructive Inspection (NDI) Shop in Little Rock, Arkansas, for example, use this type of tool to help them see cracks and other imperfections in aircraft parts that are capable of taking down a plane. One such inspection uses liquids to help illuminate potential dangers that are otherwise undetectable. That is incredible! Problem is, those processes generate chemicals.
The latest nondestructive inspection process is computed radiography, which is similar to an ultrasound, scan, or MRI for ill patients. The new digital technology will replace the X-ray film used by approximately 1,200 Air Force NDI technicians over the next few years, thus eliminating the chemical process and keeping those toxins out of waste streams. Additionally, it may well affect every airframe.
“Every aircraft that we fly in the Air Force—whether it’s a manned or an unmanned—has some level of inspections that are required on a reoccurring basis,” said Michael Paulk, Air Force NDI Office chief. Nondestructive inspections are performed on many parts of an aircraft either after a specific number of operating hours are reached or after an aircraft encounters severe flying conditions or hard landings to determine the existence and extent of damage.
In addition to being more accurate and better environmentally, the new digital format will save money. The price to buy 50 sheets of X-ray film is about the same as buying one digital plate—a plate good for 500 uses. Plus, the digital format lets NDI technicians enhance images for clarity if needed or electronically share them with experts for second opinions.
Deployment comes easier, as well. The new equipment will fit on one pallet instead of four, saving precious cargo space and setup time on arrival—from at least two days down to four hours. The Air Force Life Cycle Management Center is training technicians on the equipment, which is expected to replace all legacy systems within five years.
“Just like the doctor might do an ultrasound, an MRI, or an X-ray, we do basically the same thing to our patients, which are airplanes and the components of airplanes,” Paulk added.