What happened
During the takeoff roll, the aircraft experienced an uncontained failure of the No. 4 engine. Following the failure, the crew rejected the takeoff, and the aircraft came to a stop on the remaining runway. After the engine failed, a fire erupted within the engine, which was subsequently extinguished by airport emergency personnel.
The investigation
An examination of the aircraft revealed that debris released during the engine failure caused damage to several components, including the engine, pylon, right wing, flaps, aileron, right horizontal stabilizer, and the fuselage.
Upon inspection of the engine, investigators determined that the fifth stage hub of the low pressure turbine had ruptured. This rupture caused approximately 180 degrees of the hub rim to separate, taking the blade attachment slots and blades with it. The investigation found that the rupture originated from a well oxidized, intergranular fracture at a tierod hole. No apparent defect was observed along the edge of the tierod hole that would have caused a crack to initiate or propagate to a critical length.