What happened
On June 11, 2010, a Boeing 747-400F, registered JA01KZ, operated by Nippon Cargo Airlines, departed Narita International Airport for Anchorage, USA. Shortly after lifting off from runway 16R, the aircraft experienced a sudden abnormal noise and a significant drop in performance from the No. 1 engine. The flight crew noted a sharp decline in N1 and N2 speeds and a temporary spike in exhaust gas temperature. The aircraft initially veered slightly to the left before the pilot corrected the heading and engaged the autopilot.
After climbing to 7,000 feet, the crew shut down the malfunctioning No. 1 engine. To prepare for an emergency return, the crew jettisoned approximately 150,000 pounds of fuel. The aircraft landed safely back at Narita International Airport at 23:08. There were no injuries to the three persons on board.
The investigation
The JTSB investigation involved a detailed teardown of the General Electric CF6-80C2B1F engine. Inspections were conducted in Taiwan and the United States, including borescope examinations and laboratory analysis of the high-pressure turbine (HPT) blades. Investigators examined the engine's maintenance history, noting that while regular borescope inspections had been performed, the specific area of damage—the blade shanks—was not visible during standard inspections. The investigation also reviewed the presence of corrosive substances, such as sodium and sulfates, within the engine components.
Findings
Technical examinations revealed extensive internal damage to the No. 1 engine. Specifically, four of the 80 stage 1 HPT blades had fractured at the root, and all other blades in the stage 1 and stage 2 HPT sections were damaged. This fragmentation caused secondary damage to the nozzle guide vanes (NGV), the HPT shroud, and various downstream components, including the low-pressure turbine (LPT) vanes and blades.
The primary cause of the blade fractures was identified as pitting due to type II hot corrosion occurring in the shank area of the stage 1 HPT blades. This corrosion, likely driven by sulfur in the jet fuel and environmental contaminants, created pits that developed into fatigue cracks under operational stress. Because the shank area is obscured from view during routine borescope inspections, the degradation went undetected until the structural failure occurred.