Investigators have yet to establish the root cause of a fan-blade fracture involved in an engine failure affecting an Air France Airbus A380.

The US FAA states that the reason for the first-stage low-pressure compressor blade fracture is “still undetermined” in an interim directive requiring further precautionary action on Engine Alliance GP7200 powerplants.

Its directive refers to an in-flight shutdown on a 10 March 2019 service, following the fracture of two first-stage low-pressure compressor blades. While it does not specify the airframe involved, an Air France A380 returned to Abidjan with GP7200 failure on this date.

“After an analysis of these fractures, the manufacturer determined the fan blades experienced cracks that originated on the internal surface of the convex airfoil and propagated to the point of failure,” states the FAA.

“The cracks originated in a microtexture area that can result in a low-cycle fatigue debit that may allow a crack to initiate and propagate to failure.”

Operators with GP7200-powered A380s with certain blades fitted are being instructed to conduct ultrasonic inspections and replace any blades which fail the check. Blades which have undertaken 3,250 cycles or more since new must be checked within 250 cycles.

The measures take effect from 14 January.

Air France had already experienced a serious engine failure on an A380 operating over Greenland in September 2017, resulting in a number of directives requiring component checks.