Boeing has suspended 737 Max flights after being notified by engine supplierCFM Internationalabout a "quality concern" in low pressure turbine discs inside Leap-1B engines.

It is not clear how the suspension will affect the precise timing of the first 737 Max 8 delivery toLion AirGroup subsidiaryMalindo, but Boeing and CFM say they still plan to start delivering the re-engined aircraft to customers later this month. Production of the 737 Max and 737NG aircraft also will continue.

“We are working with CFM to inspect the discs in question,” Boeing says.

Boeing adds that it has not detected any issue with the LPT discs in 737 Max flight tests to date. The 737-8 received an airworthiness certificate in March, and the stretched 737-9 entered flight testing last month.

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The LPT for the Leap-1B is designed by CFM joint venture partnerSnecmaand features titanium-aluminide blades, although the same material is not found in the discs that were affected by the quality issue, which was discovered during inspections in the manufacturing process.

Boeing has flown more than 2,000h on 737 Max 8 aircraft powered by 27,000lb-thrust Leap-1B engines.

Boeing also completed a cycle of testing in April to qualify for 180min extended operations (ETOPS), which required simulating 3,000 flight cycles on the test stand to demonstrate reliability.

CFM promises to improve the specific fuel consumption of the Leap-1B by 12% compared to CFM56 engines on the 737NG fleet. In addition to titanium-aluminide blades in the LPT, the Leap-1B features 3D-wove, composite fan blades and fan case and ceramic matrix composites in the second-stage high-pressure turbine shrouds.