Martinair MD11 at Tenerife on Mar 9th 2014, uncontained engine failure

Last Update: November 22, 2016 / 17:43:59 GMT/Zulu time

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Incident Facts

Date of incident
Mar 9, 2014

Classification
Incident

Airline
Martinair

Flight number
MP-71

Aircraft Registration
PH-MCU

ICAO Type Designator
MD11

A Martinair Cargo McDonnell Douglas MD-11 freighter, registration PH-MCU performing flight MP-71 from Tenerife Sur Reina Sofia,CI (Spain) to Sao Paulo Viracopos,SP (Brazil), was in the initial climb out of Tenerife South Airport's runway 08 when the right hand engine (PW4462, #3) emitted a loud bang forcing the crew to shut the engine down. The aircraft stopped the climb at 7000 feet and returned to Tenerife's runway 08 for a safe landing about 40 minutes after departure.

On Apr 25th 2014 the Dutch Onderzoeksraad (DSB) confirmed in their quarterly bulletin, that the engine suffered an uncontained failure of the low pressure turbine followed by an engine #3 fire indication. The DSB stated: "This serious incident is a so-called "uncontained engine failure and poses a safety for passengers and aircraft systems, including the control and fuel systems." Spain's CIAIAC is investigating the serious incident.

On Mar 30th 2015 Spain's CIAIAC reported in an interim statement that the aircraft was in the initial climb when the crew heard unusual noise and noticed the aircraft yawed to the right. Shortly afterwards vibrations began and engine #3 parameters became abnormal, N2 showed 105% with the EGT at 875 degrees C. The crew began to work the related checklists, while working the checklist the fire alarm for engine #3 activated. The crew continued to work the checklist engine severe damage or fire, shut the engine down, discharged the first fire bottle after which the fire alert ceased. The crew decided to return to Tenerife, dumped fuel at FL070 and returned to Tenerife South Airport. Once landed the crew realized an uncontained failure of the right hand engine #3 caused by a blade failure. The aircraft received damaage to the #3 engine nacelle and #3 pylon, right wing and horizontal stabilizer. The engine mainly showed damage to all stages of the low pressure turbine, the second stage of the high pressure turbine has been sent for further examination and metallographic analysis. The occurrence was rated a serious incident, the investigation is continuing.

On Nov 22nd 2016 Spain's CIAIAC released their final report concluding the probable causes of the incident were:

The failure of the aircraft’s no. 3 engine occurred due to the detachment of a vane in vane cluster 22 in the 4th stage stator of the low-pressure turbine (LPT).

The root cause of this failure was probably the pressure pulses (HPT 2E excitation) generated by the second stage of the high-pressure turbine (HPT), which caused elevated levels of vibration in the LPT 4th stage stator, resulting in fatigue cracks forming on the vanes.

Although the investigation has not been able to determine if the corrosion was a contributing factor in the development of the failure, this mechanism cannot be rule out.

The CIAIAC reported that during initial climb the crew heard a loud bang and noticed a yaw to the right. A short while later they felt vibrations and noticed abnormal indications for the #3 engine showing 105% N2 and 875 degrees C EGT. The crew concluded that the engine had received substantial damage and worked the related checklist. While working the checklist the fire indication for the #3 engine activated but ceased after the first bottle of fire extinguisher had been discharged as part of the checklist valid for both substantial engine damage and engine fire.

As the aircraft was controllable and the fire indication was off, the crew decided to dump fuel before the return to Tenerife. Following landing without further incidents it was discovered the #3 engine had suffered an uncontained engine failure, there were no signs of a fuel, hydraulic or oil leak.

The aircraft received damage consistent with the ejection of parts from the right hand engine including:

- Wing leading edge
- Underside of the wing
- Winglet
- Inboard and outboard flaps
- Flap rail housing (inboard, middle and outboard)
- Inboard aileron
- Horizontal stabilizer

The #3 engine had last undergone overhaul in September 2010. The LPT had since accumualted 25,597 flight hours in 5,002 flight cycles.

An inspection of the #3 engine revealed:

- Blades in stage 3 rotor: damaged, in proper position
- Vanes in stage 4 stator: severely damaged, some missing
- Blades in stage 4 rotor: all airfoils missing
- Vanes in stage 5 stator: severely damaged some missing.
- Blades in stage 5 rotor: all airfoils missing
- Vanes in stage 6 stator: numerous missing
- Blades in stage 6 rotor: all airfoils missing
- LPT case: penetrated from the inside outward.

An Airworthiness directive FAA-2012-14-09 became effective on Nov 7th 2012 regarding 3rd and 4th stage vane fractures in the stators of the low pressure turbine leading to uncontained failures. Compliance with the AD was required only at the next engine overhaul however. As result the AD had not been implemented on the engine, that had not yet undergone further overhaul.

The CIAIAC analysed that the crew complied with engine start up procedures, engine warm up times and engine procedures. The CIAIAC wrote: "The crew’s actions were coordinated and in keeping with the company’s guidelines, with control of the aircraft being transferred to the pilot in command. An emergency declaration (MAYDAY) was issued so as to obtain the maximum assistance from airport services and from ATC in resolving the situation. ... The crew’s actions are deemed to have been appropriate and highly professional."

The CIAIAC analysed the failure sequence: "the failure sequence most likely began in the LPT 4th stage stator, specifically with the fracture of the airfoil from vane cluster 22. This detached airfoil impacted the rotor of the same stage, which is located just behind the stator, causing every blade on the rotor to fracture at its weakest point. It is possible that those blades already had fatigue cracks which would have produced a lower strength in the area of the crack and the consequent fracture of the blade at that point. Although, it is possible that the initiating impact damage and progression occurred during the event, as the rotor was being de-cobbed. The damage found in the engine is fully consistent with a failure sequence scenario in which the lower vane in vane cluster 22 in the LPT 4th stage stator was the first to detach. The metallurgical investigation has not been able to determine if the corrosion was a contributing factor in the development of the failure, or not."

With respect to the failure scenario the CIAIAC analysed: "The pattern of mixing and assembling the blades in the HPT 2nd stage, alternating heavy and light blades, was in keeping with the latest instructions from the engine manufacturer, the main objective of which was to prevent the 2E excitation. Due to this and other conditions, the risk monitoring/evaluation conducted by the operator/manufacturer indicated that this engine was considered “safe” against the risk posed by HPT 2E excitation. In contrast, the measurement of the HPT 2nd stage rotor (see 1.16.2) revealed that the disk had a pattern of flow areas that was susceptible to producing the pressure pulses that generate the 2E excitation. From this it may be concluded that this disk’s actual condition was significantly different from the condition that would be expected based on the risk analysis. This calls into question both the reliability of this analysis and the knowledge of the factors involved in generating the pulses that result in 2E excitation."

The investigation released two safety recommendations to the engine manufacturer to quantify and eliminate the risk of 2E excitation.
Incident Facts

Date of incident
Mar 9, 2014

Classification
Incident

Airline
Martinair

Flight number
MP-71

Aircraft Registration
PH-MCU

ICAO Type Designator
MD11

This article is published under license from Avherald.com. © of text by Avherald.com.
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