What happened
On 9 March 2014, a Martinair Cargo Boeing MD-11, registration PH-MCU, was performing a scheduled international cargo flight from Amsterdam to Viracopos, Brazil, with a stopover at Tenerife South/Reina Sofía airport. During the initial climb following takeoff, the crew experienced a loud noise similar to an explosion, accompanied by a rightward yaw and a visible white flash and cloud in front of the aircraft.
Following the event, the crew observed abnormal parameters on the number 3 engine, including an N2 reading of 105% and exhaust gas temperatures reaching approximately 87/°C. This was immediately followed by a fire warning for the third engine. The crew executed the required emergency procedures, which included discharging the first fire extinguishing bottle, successfully clearing the warning.
To prepare for a safe return, the crew climbed to 7,000 feet to jettison fuel and reduce the aircraft's landing weight. The aircraft subsequently returned to Tenerife South and landed on runway 08 without further incident. A post-flight inspection revealed that the number 3 engine had suffered an uncontained failure, though no leaks of fuel, hydraulic fluid, or oil were detected.
The investigation
The CIAIAC examined the engine components, specifically focusing on the low-pressure turbine (LPT) and high-pressure turbine (HPT). Metallographic analysis of the recovered vane clusters from the 4th stage of the LPT revealed significant wear and numerous fatigue cracks.
Investigators analyzed the engine's maintenance history and the manufacturer's risk assessment. While the engine had been categorized as "safe" against specific vibration risks, the investigation found that the HPT 2nd stage rotor disk possessed a flow area pattern susceptible to generating pressure pulses. The investigation also reviewed previous incidents and manufacturer service bulletins issued by Pratt & Whitney regarding similar engine issues.
Findings
- The primary cause of the engine failure was the detachment of an airfoil from vane cluster 22 in the 4th stage stator of the low-pressure turbine.
- The root cause was identified as pressure pulses (known as HPT 2E excitation) generated by the 2nd stage of the high-pressure turbine.
- These pressure pulses induced high levels of vibration in the 4th stage LPT stator, leading to the formation of fatigue cracks in the vanes.
- The engine's risk monitoring and evaluation systems had incorrectly deemed this specific engine configuration safe from the 2E excitation phenomenon.
- There was no evidence of fuel or fluid leaks following the uncontained failure.