The fan blade that failed on a Southwest Airlines Co. plane last month, killing a passenger, had been inspected seven times since late 2012 but without the sophisticated technology airlines are now under orders to use.
The inspections relied on visual observations and there were no reports of cracks, according to a preliminary report issued Thursday by the National Transportation Safety Board.
The investigation of the April 17 Southwest flight is one of the most significant in years, since it raises questions about the safety of the CFM56-7B engine, one of the world’s most popular. Before engines like this get approval from aviation regulators, manufacturers must demonstrate that fan blades like the one that failed won’t trigger extensive damage if they break loose.
Since a similar fan blade failure on another Southwest plane in 2016, engine maker CFM International Inc. has urged airlines to use either ultrasound or electric-current tests designed to find cracks beneath the surface.
The Federal Aviation Administration has issued two orders since April’s accident for the more sophisticated testing of fan blades, touching off a rush by airlines to examine thousands of the blades. The orders call for the inspection of blades that have made at least 20,000 flights by the end of August. The failed blade had made more than 32,000 flights, according to the NTSB.
Southwest says it expects to complete all the inspections of its fleet in coming weeks.
The most recent extensive inspection of the failed blade occurred in November 2012, using a dye designed to highlight small cracks on the surface. For the six occasions after that, the blades were lubricated and mechanics examined them visually for flaws.
CFM is a joint venture between General Electric Co. and France’s Safran SA.
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