The Federal Aviation Administration has issued a new airworthiness directive (AD) requiring more-urgent inspections of highest-cycle blades in CFM International CFM56-7B turbofans on Boeing 737NG aircraft.

When the directive takes effect 31 May, carriers will have 30 days to perform eddy current or ultrasonic inspections of blades identified in a 9 May service bulletin issued by CFM.

That bulletin recommends that airlines by 30 June inspect blades with more than 20,000 cycles, and some engines with 20,000 cycles, according to GE Aviation, which co-owns CFM with Safran Aircraft Engines.

GE says some 5,400 engines fall within that category, though it also says many engines have already been inspected.

"The FAA is acting to ensure an extra measure of safety for fan blade performance in CFM56 engines," the FAA says in a statement. "Working jointly with investigators, the manufacturer and European safety regulators, the FAA is issuing an Immediately Adopted Rule that now requires an initial inspection of fan blades with the highest number of flights… within 30 days."

Immediately adopted rules take effect immediately but remain open to public comment.

Published 16 May, the rule supersedes a 2 May AD and marks the FAA's third regulatory response to the failure of a CFM56-7B turbofan on a Boeing 737-700 operated by Southwest Airlines on 17 April.

A blade released from that engine caused a cabin window to shatter, leading to the death of one person – the first fatal accident on a US passenger airline since 2009.

Similar to the 2 May directive, the new AD requires airlines to inspect all other blades prior to when they reach 20,000 cycles or within 90 days, whichever comes first.

Carriers must repeat inspections of those blades at intervals no greater than 3,000 cycles, the directive says.

The FAA's first regulatory response to the Southwest accident came as an emergency AD issued 20 April. That directive gave airlines 20 days to inspect CFM56-7B fan blades with at least 30,000 cycles.

In addition to the April Southwest incident, another CFM56-7B powering a Southwest 737-700 suffered a seemingly-similar inflight failure in 2016.

CFM has "responded aggressively" since that event. It has developed with regulators "a multi-phased inspection programme" that "will result in a full accounting and tracking" of all 356,000 CFM56-7B fan blades, says GE.

Roughly 77,000 blades have been inspected to date, GE says.

Source: Cirium Dashboard