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Summary

Summary

On commencement of the takeoff, power was increased normally and at approximately 60 kts a loud mechanical noise was heard from the right engine with the right torque meter showing large deviations. The takeoff was rejected. Smoke was then observed in the cockpit and the cabin rapidly filled with dense smoke. The aircraft was stopped on the taxiway and emergency checklist actions and evacuations procedures were carried out. All crew and passengers successfully evacuated the aircraft in a timely manner. Examination of the engine found that the primary reason for the engine failure was the failure of the number three bearing which had allowed the low pressure impeller to move forward relative to its housing, causing secondary damage and the subsequent engine failure. The bearing which had been fitted to the engine since manufacture had been removed, checked and reinstalled during the engine turbine modification upgrade about 530 hours before the incident. Subsequently during the post-incident inspection one of the bearing balls was found to be approximately 1 mm smaller than the remaining balls. The presence of the smaller ball resulted in alternating tensile stress in the bearing cage, resulting in fatigue fracture propagation through the cage ligaments at the smallest ball. The quantitative fractography of the cage fracture surface concluded that the fatigue crack appeared to have initiated near or shortly after the time of the engine turbine modification upgrade. Significant factors The following factors are considered relevant to the development of this incident. 1. One ball in the number three bearing cage was 1 mm smaller than the remaining balls. 2. The presence of the smaller ball resulted in alternating tensile stress in the bearing cage, causing fatigue fracture propagation through the cage ligaments at the smallest ball. 3. The failure of the number three bearing allowed the low pressure impeller to move forward relative to its housing causing secondary damage.
 
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