FAA and the European Aviation Safety Agency (EASA), acting on manufacturer CFM International's recommendations, have mandated a tighter timeline for initial inspections of higher-time CFM56-7B fan blades.
In airworthiness directives (ADs) published May 17, each regulator changed the deadline for inspecting blades with between 20,000 and 30,000 cycles since new to June 30. The previous deadline, established by ADs issued last month, was Aug. 31.
"It has been determined that the initial inspection for certain fan blades must be accomplished within a reduced compliance time," EASA explained, referencing a CFM service bulletin issued May 9.
The deadline for highest-time blades--those with at least 30,000 cycles--was earlier this month, while the date for inspections on blades with fewer than 20,000 cycles remains Sept. 7. Follow-up checks must be done every 3,000 cycles--the equivalent of every 18-24 months.
The first round of inspections, on the highest-time blades, does not appear to have uncovered a fleet-wide issue. Some carriers have reported removing and replacing blades, with the removed blades being sent to GE Aviation for more detailed analysis. GE and Safran are partners in CFM.
Cracked fan blades have been identified as the root causes of two CFM56-7B engine failures on Southwest Airlines Boeing 737-700s--one in August 2016 and one last month. Both have been classified by NTSB as accidents; the second resulted in a passenger fatality.
In each instance, a No 1. engine failure was linked to a cracked fan blade, with fatigue cracking within the dovetailed-shaped blade root, where the blade attached to the hub, identified as the likely cause. NTSB continues to investigate both accidents.