Mcdonnell Douglas MD-10-30F N304FE incident near Portland, Oregon

Probable cause

The fracture of the fan mid shaft due to a stress corrosion cracking initiated by local regions of corrosion pitting, which resulted from oil migration within the shaft and its subsequent degradation.

NTSB analysis

On February 13, 2012, a FedEx McDonnell Douglas (Boeing) MD10-30, registration number N304FE, equipped with three General Electric (GE) CF6-50 turbofans engines, performed a rejected take-off due to a failure of the No. 1 (left) engine. No injuries were reported. The incident flight was a regularly scheduled domestic cargo flight, operated under the provisions of Title 14 CFR Part 121, from Portland to Oakland, California. Examination of the airplane revealed no damage or penetration of the cowlings and no damage to the airplane; however, examination of the engine revealed three penetration holes and tears in low pressure turbine case and a single hole located in the turbine rear frame. Disassembly of the incident engine found that the fan mid shaft had fractured and the aft section of the fan mid shaft exhibited a spiral crack angled 45° to the longitudinal axis that measured about 69.5-inches in total length (about 3½ revolutions around the shaft) and extended about 20.5-inches axially in length. Metallurgical examination of the fan mid shaft found that it had fractured entirely in an intergranular mode. The initiation of the spiral fracture was comprised of numerous discolored, thumbnail shaped cracks initiating from the inner diameter surface of the fan mid shaft, some of which had progressed through the fan mid shaft thickness. The morphology of the cracks was consistent with a stress corrosion cracking mechanisms typical of high strength steel such as the fan mid shaft parent material. Localized areas of corrosion pitting, scaling, and loss of the anti-corrosion coating were observed throughout the inner diameter of the fan mid shaft. Examination of the debris within the shaft identified it as an ester based engine oil residue, typical of the kind of oil used in turbine engines. The stress corrosion cracking observed on the fan mid shaft was caused primarily due to the breakdown of a synthetic oil product inside the FMS during both storage and engine operation. The exact source or mechanism by which the oil entered the dry cavity between the fan mid shaft and the center vent tube is unknown.

Text from the NTSB. Open the NTSB docket for ENG12IA012 for the full record.