Air Berlin A332 at Phuket on Dec 20th 2012, uncontained engine failure and fire

Last Update: November 1, 2023 / 20:28:55 GMT/Zulu time

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Incident Facts

Date of incident
Dec 20, 2012

Classification
Incident

Airline
Air Berlin

Aircraft Registration
D-AXBA

Aircraft Type
Airbus A330-200

ICAO Type Designator
A332

On Nov 1st 2023 Germany's BFU released their final report concluding the probable causes of the serious incident were:

Immediate Cause:

This Serious Incident was caused by a leak in the green hydraulic system following an engine failure in a location, where the available information and the associated procedure would not have been suitable to stop the leakage and thus maintain the functionality of this hydraulic system for the remainder of the flight.

The Serious Incident was also caused by the limited capability of the flight crew to assess the developing situation and manage it.

Systemic Cause:

The Serious Incident was caused by the fact, that the established procedures to ensure flight safety, especially the existing SMS and the training syllabus of the operator, were not adequate to prepare the flight crew for this multi-failure scenario.

The BFU analysed:

Left Engine Damage

The flight crew noticed the engine damage because of the sounds and vibrations, the warnings and the ECAM information. The thrust lever of the left engine was pulled back. Because engine thrust was reduced, the EGT and N2 threshold values were no longer exceeded and the vibration level decreased. The engine operated in N1 mode.

It can be assumed that in this phase no further engine damage occurred.

Even though the PIC assumed “severe” engine damage and wanted to shut off the engine, the flight crew followed the ECAM actions because they quickly wanted to regain a high degree of automatic flight. When FADEC recovered the capability to operate in EPR mode, the ECAM action ENG EPR MODE RECOVERABLE was triggered. When the crew selected the N1 mode off, the FADEC resumed the operation in EPR mode.

After the EPR mode had been re-established, the FADEC aimed at thrust increase (defined by a certain EPR value). Due to the mechanical damage at the LPT, the engine was not able to attain the commanded EPR level. Even though the thrust lever was in the IDLE position, the threshold value (EGT) was repeatedly exceeded. This resulted in engine shut-down by the flight crew.

According to the procedures in the FCOM Abnormal and Emergency Procedures, PRO-ABN-70 Powerplant:

• ENG 1(2) EGT OVERLIMIT
• ENG 1(2) N1/N2 OVERLIMIT

the engine has to be shut down if the parameters cannot be met. These procedures were available to the flight crew.

The FDR data showed that operation in N1 mode was possible without EGT/N2 exceedance, whereas this was not possible in EPR mode. Therefore, with this damage, the attempt to operate the engine in EPR mode again could not be successful and ultimately resulted in the shut-down, as it was stipulated in the above-mentioned procedures.

Airbus issued the Flight Operations Briefing Note (Handling Engine Malfunctions) to give flight crews indications for the further use of engines.

The decision to shut off the engine or operate it in Flight Idle is the first essential decision for the further course for the flight. Had the engine been operated in Flight Idle, auxiliary units such as the hydraulic pumps of the green and blue hydraulic systems would have remained powered. If the blue system had remained powered and therefore fully functional, the later problems would have been significantly minimised. On the other hand, engine shut-off was a safe option to prevent further damage. It cannot be assessed if continued operation of the engine would have been possible without increasing the damage significantly. After the engine was shut off, it was possible to eliminate further damage of the engine and the thermal load of the pylon.

The flight crew decided at their own discretion to shut off the engine. This had the effect that the engine was not available as energy source for the hydraulic pump of the blue hydraulic system and that the green hydraulic system still continued to run empty.

The PIC's decision to shut down the engine is understandable based on the observations. The procedures ENG 1(2) EGT OVERLIMIT and ENG 1(2) N1/N2 OVERLIMIT confirm these actions.

Double Hydraulic System Failure

After the left engine was shut down, pressure in the blue hydraulic system was maintained for about 20 min. Due to configuring the aircraft for the approach and the related decrease of airspeed, the blue hydraulic system no longer supplied any pressure because of lack of windmilling (decreasing RPM of the N2 rotor). It was not possible to anticipate the leakage of the green hydraulic system.

The completion of the ECAM actions is of particular importance. The flight crew was made aware of the leakage of the green hydraulic system for the first time by the warning HYD G SYS LEAK.

In particular, the co-pilot had difficulties to understand the meaning of the instruction LEAK RATE MONITOR. This is apparent by the CVR recording where the flight crew talks about values of “3,050”, then “3,000” and finally “2,901” (without any units). The co-pilot’s comment “Ja, die decreased (Yes, it decreased). Also wir haben jetzt dreitausend, die bleibt eigentlich so (now we have 3,000 it actually stays the same, now)” is contradictory and shows that the flight crew had not assessed the available information correctly. It is obvious that the hydraulic pressure was interpreted as Leak Rate.

At the hydraulic page, only the reservoir and the hydraulic pressure were indicated, but not the leak rate.

...

Determining the Leak Rate would require several minutes. The flight crew would have to wait for this process to end to ensure the correct completion of ECAM actions. It is not conceivable that during this period no (other) interruptions occur. According to the statements made in Chapter 2.4.5 a comparatively long work step and the subsequent high number of expected interruptions is extremely error prone. Since such ECAM actions only appear during technical failures and normally require the completion of abnormal procedures, the contradictory indication increases the workload of the flight crew.

This had the effect that the ECAM action LEAK RATE MONITOR was not completed and the hydraulic pumps of the green hydraulic system’s engines were not switched off. During leakage in the pressure pipe, switching off the pump would have resulted in decrease or termination of the leakage. In this case switching off the pump would not have changed anything in regard to the leakage, because in the Case Drain Line is always a volume flow, according to the manufacturer.

Due to the decrease in airspeed and the resulting reduction of the left engine RPM the pressure in the blue hydraulic system dropped. This triggered the Blue System Low Pressure warning. After the landing gear had been extended, more hydraulic fluid flowed from the reservoir. This triggered the warning HYD G+B SYS LO PR at 1421:42 UTC. The loss of the pressure of the green hydraulic system was a result of the closure of FSOV 1 and 2. At that time, the aircraft had only the yellow hydraulic system available. The functions of the green and blue hydraulic systems were no longer available. The aircraft was operated in Alternate Law and the landing gear could no longer be retracted.

Aircraft Damage

The examination of the left pylon determined a range of damage. It is highly likely that the majority of the damage were connected to the engine damage and the resulting increased vibrations. The assessment of the fatigue failure at the hydraulic line bracket was of particular interest. If it had fractured prior to the engine damage, the free oscillating line could have facilitated the loosening of the pump drain line. Due to the missing information as to the beginning of the fatigue failure, it was not possible to express an opinion. The same is true for the other damage of the pylon.

It has to be assumed that the landing gear wheels were damage during their blockage.

Engine

The damage the investigation revealed allows the conclusion that the point of origin was the 4th LPT guide vane stage. This is proved by the fact that the blades of the 3rd LPT stage were present, whereas the blades of the 4th stage had been torn off. The same is true for the damage at the LPT front case which also starts behind the 3rd stage.

The indications of high cycle fatigue found at nine rotor blades of the 4th LPT stage can be explained by the rubbed in notches on the blades’ leading edges. These are the results of contact with the vane clusters of the 4th stage which were lying upstream of these blades. It is highly likely that the rubbed in notches resulted in fatigue fracture at one blade which in turn caused more damage at neighbouring blades and on all following LPT stages.

The rubbed in notches at the leading edges of the blades of the 4th LPT stage corresponded in regard to their positions and extent with the damage at the trailing edge of the inner sealing ring of the vane cluster. Because there were no indications that the rotor had changed position, it has to be assumed that non-rotating parts, in this case the vane clusters, changed positions. The structure failure of the vane cluster gussets has to be viewed as cause of the change of position. The flawed geometry originating in the production process of the vane cluster gussets resulted in cracks and ultimately in structure failure. During previous maintenance actions all 44 vane clusters were replaced by new ones. They had been manufactured prior to 2010. Therefore, it has to be assumed that the missing vane cluster A also featured the flawed geometry.

The engine manufacturer was aware of the flawed geometry of the vane clusters of the 4th LPT stage due to failures of the similar model PW4000-94. The reason for their flawed geometry was also a flawed casting procedure. Had the actions then initiated been applied to vane clusters with the Casting Integral Marking 51N554AT 1447 1S2C3A earlier replacement on engines of the PW4000-100 models would have been the result. The corrective measures initiated in September 2010 could not become effective since the LPT of the engine involved had been repaired already in December 2008.

Hydraulic System

The BFU is of the opinion that the leakage of the green hydraulic system at the drain line of the left EDP was caused by increased vibrations during the engine damage. It is unlikely that two failures of this type (engine damage and leakage) occur simultaneously and independent of each other. The chronological consideration of the warnings of the reservoir’s fill quantity does not allow drawing an unambiguous conclusion as to when the leakage started and if the drainage was linear.

...

Actions after the Engine Damage

The flight crew identified the engine damage immediately as “Engine Failure“ and the PIC made a corresponding call-out. The left engine was correctly identified as cause and its thrust reduced.

Without further analysis of the engine damage, completion of the ECAM actions and confirmation from the PIC, the co-pilot made the decision for the Mayday call and the return to Phuket.

After the engine parameters had once again exceeded the limits, the PIC decided to shut off the engine without further communication with the co-pilot. Considering the consequences of this decision this communication should have taken place.

ECAM

During the damage on the engine and the hydraulic systems, the ECAM indicated the procedures required to be completed. In accordance with the FCOM, the flight crew would have had to complete and confirm them with respective call outs.

Immediately after the engine damage, the flight crew carried out these instructions.

Typical of this phase was that the completion was interrupted repeatedly, the ECAM actions were not implemented right away and the interruptions and the completion, respectively, were not confirmed with the stipulated call-outs „Stop ECAM“, „Continue ECAM“ and „ECAM Completed“.

As the flight progressed, the ECAM instructions were no longer fully executed when failure messages occurred. For example, after the ECAM warning HYD G SYS LEAK the corresponding ECAM procedure was begun. The call-out stipulated in the FCOM was not made. Between 1415:20 UTC and 1416:13 UTC and then later between 1417:23 and 1417:40 UTC, individual steps of the ECAM action were carried out. This resulted in the fact that the not completed ECAM action to shut off the hydraulic pumps remained unnoticed (Chapter 2.2.2). The completion of the ECAM action was interrupted by the approach planning and the transition of control. The PIC’s statements show that he attached very little importance to ECAM in this phase.

After the HYD G SYS LEAK and HYD G+B LO PR indications, no other ECAM actions were carried out any more.

The correct handling of the ECAM actions was repeatedly disregarded and finally stopped.

During the completion of complex abnormal/emergency procedures it is very difficult to recognise an erroneous ECAM completion or to reverse it due to doubts or start from the beginning. The SaMSys Study showed that none of the 120 pilots repeated the ECAM action or began again from the start due to doubts or working errors. Accurate ECAM completion must have the highest priority.
Incident Facts

Date of incident
Dec 20, 2012

Classification
Incident

Airline
Air Berlin

Aircraft Registration
D-AXBA

Aircraft Type
Airbus A330-200

ICAO Type Designator
A332

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