FAA has mandated inspections for the CFM56-7B fan blade population not covered by the agency’s April 20 emergency airworthiness directive (AD), following CFM International’s latest recommendations.
The new AD, set for publication May 2 and effective May 12, orders operators to conduct ultrasonic or eddy current inspections on CFM56-7B fan blades before they reach 20,000 cycles.
Blades with 20,000-30,000 cycles, or blades where the age is not known, must be inspected by Aug. 31, or within 113 days of the directive’s effective date. Blades with 30,000 or more cycles were the target of the April 20 AD.
The new directive also requires follow-up checks every 3,000 cycles—roughly two years of typical Boeing 737NG airline service. FAA said the AD covers about 3,700 engines.
FAA’s new AD means its 737NG engine fan-blade inspection mandates now align with what the European Aviation Safety Agency (EASA) required in its April 20 directive—all but guaranteeing worldwide adoption by other civil aviation authorities. FAA said in its April 20 order targeting the highest-risk blades that it would likely follow up with requirements on the broader population.
All the mandates are based on a CFM International service bulletin (SB) that was updated in the wake of the April 17 engine failure onboard a Southwest Airlines 737-700 that resulted in the death of one passenger. The original SB was issued after a similar accident in August 2016 involving a different Southwest 737-700.
In both accidents, an engine failure apparently originated when one of each engine’s 24 fan blades fractured near the fan hub. Damage patterns included shredded fan cowlings and debris that broke away and struck the fuselage. In last month’s accident, debris damaged a passenger window, causing the cabin to lose pressure and fatally injuring the window’s closest passenger.
CFM said late last week that initial checks on the highest-cycle engines had not turned up any fleetwide concerns. Operators are replacing blades, however, as part of routine maintenance. CFM said it has sufficient spare parts to meet anticipated demand.
Southwest, which has fast-tracked a fleetwide inspection program put in place after CFM’s initial recommendations in 2017, said April 26 it has found one cracked blade in about 25,500 inspections since the program was put in place.