History of the Flight
On September 6, 1997, scheduled passenger flight CP30 was operating from Beijing to Vancouver, British Columbia. The augmented crew had flown the aircraft into Beijing the previous day and reported normal inbound and departure start-up. Shortly after commencing the take-off roll, at about 20 knots as the engines neared 40-degree Celsius rated take-off thrust, a loud explosion occurred. The aircraft vibrated and yawed sharply to the left. The take-off was immediately rejected, and within seconds a fire warning activated for the left engine. The augmenting first officer, seated in the cockpit jump seat, quickly went to the cabin and visually confirmed a fire in the left engine. The captain and operating first officer performed emergency procedures. After the second fire bottle was used, the fire warning ceased, and the augmenting first officer visually confirmed the fire was out. Emergency response personnel also confirmed extinguishment. Passengers deplaned via normal exits after the aircraft was towed to the terminal. A post-shutdown inspection revealed that parts from the high-pressure compressor (HPC) had detached from the engine.
Injuries and Damage
Neither crew nor passengers sustained fatal or serious injuries. The 10 crew members and 199 passengers reported minor or no injuries. The aircraft suffered damage: approximately 30 kilograms of rotating hardware from the left engine HPC and compressor case were found on the ground near the aircraft. Debris penetrated the left-engine casings, inboard reverser, and translating cowls. A 1.5-inch long puncture was found in the fuselage adjacent to the left-wing root, just forward of Station 720, but no engine debris entered the passenger cabin. The left-hand high-speed (inboard) aileron had three punctures in the lower skin. Engine teardown at Motoren- und Turbinen-Union (MTU) in Hannover, Germany, revealed damage to the internal rotating structure.
Cause of Failure
The uncontained failure of the left engine resulted from a fracture of the third stage of the 3-9 HPC spool. The fatigue crack initiated near the dove-tail slot bottom, a high-stress area subject to about 75 per cent of the minimum yield strength of the Ti 6242 alloy. At failure, approximately 45 per cent of the third-stage cross-section was pre-cracked; the remainder failed suddenly in overload under take-off thrust. The crack originated from an oxygen-rich segregate in the titanium batch used for the 3-5 stages of the spool. This segregate caused locally degraded resistance to fatigue crack initiation. The part failed at 4,744 cycles, well below its approved service life of 15,000 cycles. The ingestion event leading to an unscheduled overhaul in 1994-95 was not a factor.
Contributing Factors
The Board identified several contributing elements. Quality control decisions during titanium manufacture allowed the oxygen-rich segregate to remain undetected. Irregularities occurred during ingot production: the first melt's quality was uncertain, and a second-melt pressure excursion to 950 microns (within then-current limits of 1,000 microns steady-state and 6,000 microns excursion for two minutes) was discussed with the engine manufacturer, who decided the material was usable. Current RMI specifications would reject such an excursion. Additionally, existing in-service non-destructive inspection techniques could not detect altered microstructure like the segregate. The spool design was intolerant of slightly degraded material, contributing to the failure.