Jet2 B738 at Ibiza on Jul 21st 2011, engine shut down in flight
Last Update: November 6, 2012 / 17:16:47 GMT/Zulu time
the failure of the #4 bearing, which in turn failed due to spalling, or flaking of the material on the outer raceway and on the rollers. The engine manufacturer is aware of this failure mode. It happens relatively infrequently and its occurrence is actively tracked. Spalling is the subject of a few prevention campaigns.
The aircraft departed Ibiza's runway 06 with the first officer (28, ATPL, 3,086 hours total, 687 hours on type) being pilot flying, when a few seconds after the main wheels lifted off the runway a series of "detonations" were heard inside and outside the aircraft originating from the right hand engine. Ibiza tower observed streaks of flames from the right hand engine exhaust. The crew initially thought they had blown a tyre and delayed gear retraction until they realised 26 seconds later the right hand engine had failed. They then retracted the gear, declared Mayday and continued the climb with both engines operating. About 50 seconds later, with the vibrations from the right hand engine increasing and EGT beginning to exceed limits, the crew initiated the engine shut down. After reaching acceleration altitude (1000 feet) the crew accelerated the aircraft retracting the flaps and continued the climb to 3000 feet. Upon reaching 3000 feet the crew reported there was no (engine) fire and requested to enter a hold to run the checklists. The aircraft was handed off to Palma Mallorca Approach to facilitate the hold. The captain (42, ATPL, 10,900 hours total, 250 hours on type) subsequently decided to divert to Palma Mallorca although the "Engine Severe Damage or Separation" checklist required landing at the nearest airport. The captain reasoned to keep the aircraft away from built up areas, the facilities available in Palma included two parallel runways at Palma, and they were at a position nearly equidistant to Ibiza and Palma. The crew subsequently confirmed their roles with the first officer being pilot flying and the captain being pilot monitoring, briefed the approach and go-around for Palma and landed safely on Palma Mallorca's runway 24L about 40 minutes after becoming airborne.
The #4 bearing, located at the high pressure turbine supporting the high pressure spool shaft, is mainly exposed to radial loads as result of aerodynamic loads of the turbine as well as relatively high temperatures. Since introduction of the engine type several failures of the bearing had thus occurred, mainly caused by the "spalling" flaking or chipping off the surface of the rollers contacting the outer race of the bearing. Between 1998 and 2010 the manufacturer had changed the specifications of the materials a number of times resulting in a reduction of the shut down rate of 4 shut downs per one million flights in the beginning to 0.52 shut downs per million flights in the end. The manufacturer stated that in 30% of these cases errors in the production/assembly of the bearings led to the failure, while 3% of the cases were attributed to pollution during handling and 17% to quality control issues. The remaining 50% of cases could not be attributed.
The failure of bearing #4 led to slight blade damage in the high pressure compressor and substantial blade damage in the high pressure turbine. Analysis of the #4 bearing confirmed the bearing and its materials matched required specifications.
The CIAIAC analysed that the "detonations" heard were in fact compressor stalls as result of the blade tip damage and slightly reduced rpms following the #4 bearing failure resulting in air flow disruption throughout the engine making flames of the engine's combustion visible at the engine outlet as streaks of flame.
Laboratory examination showed outer race and rollers in an angular sector of about 90 degrees had suffered surface damage causing an imbalance. However, none of the engine monitoring sensors had recorded anything out of the normal prior to the incident flight, there had been no anomaly with the engine's chip detector or engine vibrations. The laboratory tests were not able to identify the location where spalling began.
No safety recommendation was released as result of the investigation.
This article is published under license from Avherald.com. © of text by Avherald.com.
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