What happened
On July 28, 2010, a United Airlines Boeing 777-20 and registered N219UA departed Narita International Airport for San Francisco International Airport. Shortly after takeoff, while the aircraft was climbing through approximately 11,700 feet, the right engine experienced a sudden and violent failure. The flight crew reported hearing a loud bang and a whining noise, followed by a significant yaw to the right.
Following the engine malfunction, the crew declared an emergency and initiated procedures to return to Narita. To reduce the aircraft's weight for landing, the crew began jettisoning fuel. Despite the aircraft landing at a weight of approximately 473,000 lb—which exceeded the maximum allowable landing weight of 460,000 lb—the aircraft landed safely on Runway 16R. There were 270 people on board, including 255 passengers and 15 crew members, and no injuries were reported.
The investigation
The Japan Transport Safety Board (JTSB) conducted an investigation involving a detailed teardown of the engine and an examination of maintenance records. Investigators analyzed data from the digital flight data recorder (DFDR) and performed a borescope inspection of the engine's internal components. The inspection revealed that the high-pressure compressor (HPC) was severely damaged, with broken blades and vanes, and the interior of the engine was coated in a dust-like debris.
Findings
Technical analysis determined that the failure of a lever arm connected to the inlet guide vanes (IGV) synchronizing ring was the primary cause of the incident. The investigation found that a pin within the ring had escaped its housing, causing the associated lever arm to move uncontrollably and deform into a Z-shape. This mechanical failure caused the vanes to settle in a closed position, obstructing airflow and creating pulsating air pressure within the engine.
This unstable airflow led to high-frequency fatigue, which caused the 5th-stage HPC rotor blades to break, followed by a rapid succession of failures in other compressor components and the low-pressure compressor (LPC) blades. Furthermore, investigators identified evidence of improper previous repairs on the synchronizing ring. Specifically, the welds on the pins were found to be defective, with cracks and cavities suggesting that the repair work was not performed according to the manufacturer's specified procedures.