Manufacturing Defect in GE Engine Gearshaft Leads to In-Flight Shutdown

Casualties unknown • Bering Sea, KR

A Korean Air Lines Boeing 777-300ER experienced a left engine shutdown over the Bering Sea due to a fractured radial gearshaft caused by a manufacturing error.

What happened

On July 2, 2013, a Korean Air Lines Boeing 777-300ER, registration HL8275, experienced an in-flight shutdown of its number one (left) engine while flying over the Bering Sea. The aircraft, powered by two General Electric GE90-115B engines, was operating a scheduled international flight from Chicago O'Hare to Seoul Incheon. Following the engine failure, the flight crew diverted the aircraft to Ugolny Airport in Siberia, Russia. The aircraft landed safely without injuries to the passengers or crew.

The investigation

Following an initial notification from the Korean ARAIB, the NTSB assumed responsibility for the investigation. Upon landing, technicians discovered that the transfer gearbox (TGB) housing of the left engine had fractured, causing damage to the internal gears. The engine was subsequently removed and sent to GE facilities in both Wales and Ohio for detailed metallurgical analysis.

Investigators examined the radial gearshaft, a critical component within the TGB. The examination revealed several X-shaped cracks and a primary 0.049-inch axial crack at the shaft-to-web transition radius. Scanning Electron Microscope (SEM) analysis showed fatigue propagation features. Furthermore, microhardness testing revealed that the surface of the shaft had a lower hardness level than required by the part drawings.

Findings

Technical analysis determined that the failure originated from a manufacturing process deficiency related to the carburization of the gearshaft. During production, the area of the shaft that required copper plating to prevent carbon depletion was insufficiently protected due to thin or detached plating. This led to decarburization, a process where the surface carbon levels were depleted during the hardening cycle.

This decarburization resulted in high residual tensile stresses on the outer diameter of the shaft. When combined with the standard operating stresses of the engine, these stresses triggered the initial axial crack, which eventually propagated into the observed X-shaped fatigue cracks. GE confirmed that this specific failure was part of a broader issue involving various production lots of the radial gearshaft.

Probable cause

The primary cause of the engine shutdown was the fracture of the radial gearshaft, which was driven by a manufacturing defect. Specifically, inadequate copper plating during the carburization process led to surface decarburization, creating high residual tensile stresses that initiated fatigue cracking.

Frequently asked questions

What happened in the 2014-02-20 Korean Airlines Boeing B777-300ER, registration HL8275 accident near Bering Sea, KR?

A Korean Air Lines Boeing 777-300ER experienced a left engine shutdown over the Bering Sea due to a fractured radial gearshaft caused by a manufacturing error.

What aircraft was involved and where did it happen?

The accident on 2014-02-20 involved a Korean Airlines Boeing B777-300ER, registration HL8275, registration HL8275, at Bering Sea, KR.

What was the probable cause of the accident?

The primary cause of the engine shutdown was the fracture of the radial gearshaft, which was driven by a manufacturing defect. Specifically, inadequate copper plating during the carburization process led to surface decarburization, creating high residual tensile stresses that initiated fatigue cracking.

Loading the flight search…