What happened
On 06 September 1997, a scheduled passenger flight, CP3_0, was performing a takeoff from Beijing, bound for Vancouver, British Columbia. During the takeoff roll, once the aircraft reached approximately 20 knots, a loud explosion occurred, followed by a sharp left yaw and significant vibration. The flight crew immediately rejected the takeoff.
Following the explosion, a fire warning was triggered for the left engine. An augmenting pilot visually confirmed an active fire in the engine. The crew executed emergency procedures, utilizing two fire bottles to suppress the flames. Once the fire was extinguished and the aircraft was towed to the terminal, passengers were able to deplane safely through standard exits. No injuries were reported among the 209 passengers and crew.
While the cabin remained intact, the aircraft sustained significant damage. Approximately 30 kilograms of engine hardware were found scattered on the ground near the runway. Debris from the engine penetrated the engine casings, the inboard reverser, and the translating cowls. A puncture was also discovered in the fuselage near the left-wing root, and the left-hand inboard aileron sustained three punctures.
The investigation
Investigators examined the left engine and discovered that components of the high-pressure compressor (HPC) had detached. A subsequent teardown of the engine at a facility in Germany revealed internal damage to the rotating structure.
Technical analysis focused on the failure of the third stage of the 3-9 high-pressure compressor spool. Testing showed that a fatigue fracture had initiated near the dovetail slot bottom, an area of the spool subjected to high design stresses. At the time of the failure, roughly 45 percent of the third-stage cross-section had already been compromised by pre-existing cracks, leading to a sudden overload failure as takeoff thrust was applied.
Findings
- The primary cause was an uncontained failure of the third stage of the 3-9 HPC spool caused by an oxygen-rich segregate within the titanium alloy used for the component.
- This oxygen-rich material, produced during the manufacturing process, reduced the material's resistance to fatigue crack initiation in a high-stress area of the spool.
- The segregation likely resulted from a pressure excursion during the intermediate melt of the titanium, which, while meeting the manufacturing specifications of 1989, would not have been acceptable under modern standards.
- Existing ultrasonic inspection techniques used during service were unable to detect the specific microstructure changes or the subsurface cracks in certain "blind spots" of the spool design.
- The decision to utilize the material despite the melt irregularity contributed to the occurrence.