The European Aviation Safety Agency (EASA) and the FAA late April 20 issued emergency airworthiness directives (AD) calling for inspections of fan blades on CFM56-7B engines that power Boeing 737NGs.
The emergency ADs come three days after a CFM56-7B-powered Southwest Airlines 737-700 carrying 144 passengers and five crew made an emergency landing at Philadelphia International Airport after experiencing an apparent left-engine explosion. One passenger died in the incident.
The directives follow a service bulletin (SB) engine manufacturer CFM International also issued April 20, recommending that fleet operators perform ultrasonic fan-blade inspections “within the next 20 days” on high-time CFM56-7B turbofans. The SB recommends inspections at different thresholds for all blades, with the highest-time blades—those with 30,000 or more cycles—needing inspections immediately. CFM also recommends repetitive inspections.
EASA’s AD adopts the SB, while the FAA directive only mandates one-time inspections on the highest-time blades. The FAA plans to follow up with another directive that would cover the rest of the blade population and possibly require repetitive checks.
The FAA’s directive describes its requirement as “a one-time ultrasonic inspection (USI) of all 24 fan blade dovetail concave and convex sides to detect cracking” within 20 days.Sout
EASA’s directive supersedes an AD the agency released in March, which became effective on April 2 and was in response to an August 2016 Southwest 737-700 uncontained engine failure. “Since the AD was issued, a further failure of a fan blade of a CFM56-7B engine has been reported,” EASA said.
The U.S. National Transportation Safety Board (NTSB) initially found one of the 24 titanium fan blades in the engine in the April 17 Southwest incident had separated from the fan hub, where there was evidence of fatigue cracking. The safety board has said it is too early to say if the 2016 engine failure and the latest incident are directly related.
CFM, the GE Aviation/Safran Aircraft Engines joint venture, said there are roughly 14,000 CFM56-7B engines in service. The fan-blade inspections recommended within 20 days would be for engines with more than 30,000 cycles since delivered new—each cycle consisting of an engine start, takeoff and landing, and full shut down. That affects about 681 engines worldwide, of which 150 have already been inspected, CFM said. Some 352 engines would be affected in the U.S., the FAA said.
CFM said it issued the recommendation in “close collaboration” with the FAA, EASA, Boeing and CFM56-7B operators. CFM recommends inspections “by the end of August” for fan blades with 20,000 cycles, and inspections of all other fan blades when they reach 20,000 cycles. After the first inspection, the manufacturer recommends operators repeat the inspection every 3,000 cycles, which represents about two years in airline service.
Inspections can be conducted on-wing with an ultrasonic probe along the surface of the fan blade and take about four hours per engine, CFM said.
“About 60 customers worldwide operate engines within the cyclic thresholds of the new service bulletin,” CFM stated. “CFM partners GE and Safran Aircraft Engines have about 500 technicians directly involved to support customers and minimize operational disruption.”