CFM International is monitoring its Leap engine fleet for signs of an issue believed to be tied to the March 26 contained engine failure on a Southwest Airlines 737 MAX 8 that was being ferried to storage.
The engine-maker has targeted a specific subset of Leap-1A engines that power Airbus A320neos and -1B engines found on 737 MAXs based on operational data and recommended that operators inspect the affected powerplants. The issue: carbon build up, or deposits of evaporated fuel and other material, on fuel nozzles that lead to uneven temperature flow regions within the combustion chamber exit plane and hot spots within the high-pressure turbine (HPT). These hot spots can cause premature wear.
In the case of the Southwest engine, the wear led to a turbine blade failure. Metallic fragments were found in the tailpipe, a source with knowledge of the investigation confirmed. While the investigation is ongoing, CFM believes the issue may be linked to the coking, which it has been monitoring.
CFM is working to understand not only why the Southwest engine failed, but also what is behind the carbon build-up on the fuel nozzles, of which each Leap-1B has 18.
The Southwest MAX, operating as Flight 8701, was being flown from Orlando International Airport to Victorville, Calif., to join the carrier's other MAXs in storage. About 10 min. after takeoff, the aircraft's no. 2 engine experienced a contained failure. The two-person crew returned to Orlando and landed safely.
Within hours of the failure, the company analyzed the engine's operating history—not just hours and cycles, but detailed performance data—and compared it against data from each of the other 1,560 Leaps in service. Aware of coking, a common issue with gas turbine engines but more common in some than others, the manufacturer had set up rotable pools of fuel nozzles to swap out parts at certain thresholds before the Southwest incident. Following the incident, it revised its analytics and reduced those thresholds. Engines that were beyond the revised limits were recommended for inspections.
The inspections have turned up issues on abut 1% of the engine fleet, CFM joint-venture partner GE confirmed. All of the issues have been found on Leap-1Bs.
“CFM continually monitors the fleet and we have a method to detect carbon build-up, enabling CFM and our customers to proactively manage the issue," a GE spokesperson said. "In the case of the engine on Flight 8701, we learned from the event that our monitoring analytic and maintenance process needed to be adjusted for our Leap engines. This adjustment has been made and the fleet was assessed within hours, with follow-on actions completed within days."
Southwest inspected 12 engines "that CFM identified within our fleet and handed that information over to CFM for review," a spokesperson for the airline said. "We are taking advantage of the MAX being stationary by immediately completing any routine maintenance work identified on these aircraft, that would include any potential items found during the inspection referenced."
A source with knowledge of the airline inspections told Aviation Week that Southwest removed one additional engine based on inspection findings.
American Airlines confirmed it inspected three Leap-1B engines, and reported no findings.
The 380-aircraft in-service Max fleet, powered exclusively by Leap-1Bs, has been grounded since March 13 following two fatal accidents in five months. The groundings are not tied to engine issues, but rather flight-control and training problems identified by investigators and Boeing.