On April 20, three days after a Southwest Airlines Boeing 737-700 experienced an engine failure due to a fractured fan blade, resulting in the death of a passenger, the U.S. Federal Aviation Administration issued an emergency airworthiness directive that requires operators of CFM56-7B engines with more than 30,000 flight cycles to perform a one-time ultrasonic inspection of all 24 fan blades to detect cracking.
It was the second failure of a CFM56-7B engine fan blade on a Southwest flight: a similar episode occurred in August 2016 when a fan blade broke at the engine hub and debris caused a 5-inch by 16-inch gash in the fuselage. Following that incident, the engine's manufacturer, CFM International, recommended ultrasonic inspections of fan blades on CFM56-7B engines with 20,000 cycles be completed before the end of August 2018.
The FAA mandate covers approximately 680 engines while the CFM notice affects an additional 2,500 engines. All told, that's 76,320 fan blades.
Fatigue in aircraft components and materials is obviously serious, and the FAA and CFM notices emphasize the importance of nondestructive tools and techniques in aircraft inspections and maintenance. With 31,600 commercial aircraft currently in service--the highest at any time in the jet age, according to the industry group CAPA-Centre for Aviation--and a backlog of more than 17,000 commercial aircraft on order, NDT can be part of an inspection program that keeps existing planes airworthy for as long as possible.
NDT also extends to the aftermarket. Aircraft operators and OEMs have aggressive sourcing programs that include parts and systems like landing gear that are surplus or overhauled and brought into serviceable condition. Some of these components are OEM-certified for quality, some are not. Either way, the demand underscores the need to verify the integrity of after market components.
The FAA's April 20 directive regarding CFM56-7B engines calls for the fan blades to undergo ultrasonic testing (UT), an NDT technique that uses pulses of high-frequency sound energy to detect surface and subsurface cracks and other defects. These pulses come from a transducer or probe, which a...