INVESTIGATION AND REMEDIATION OF A COMPLEX FAILURE OF A HIGH-STRENGTH STEEL FAN MIDSHAFT FROM A GENX ENGINE
Erik M MuellerChestnut
On July 28, 2012, a Boeing 787-8 airplane experienced a loss of thrust in the right GEnx turbofan engine during a pre-flight, low speed taxi test at Charleston International Airport in Charleston, South Carolina. Inspection of the engine revealed the forward end of the fan midshaft had separated, causing the low-pressure turbine rotor to shift aft, damaging that section of the engine. A detailed investigation performed by the NTSB and General Electric found the fan midshaft on the GEnx engine had separated from an environmentally assisted cracking mechanism under static load. Cracking was predicated by an intricate and previously undetected reaction between the fan midshaft ultra-high strength steel, the dry film lubricant, and the assembly aid. This investigation explored multiple and fundamental aspects of the fan midshaft, including manufacturing, assembly, design, and loading. From the investigation, a non-destructive inspection was developed and employed throughout the fleet with multiple changes to the assembly of the GEnx engine to prevent future reoccurrences.