ATSB report just out.
On 10 November 2009 at around 1900 EST, a Boeing Company 737-467 aircraft, registered VH-TJY, departed Brisbane Airport, Queensland for Melbourne, Victoria. As the aircraft was climbing through 24,000 ft, the flight crew observed abnormal indications associated with the right engine. The aircraft was returned to Brisbane where it landed without further incident.
Engine disassembly and inspection revealed significant damage to the stage-1 low-pressure turbine (LPT). Analysis of the stage-1 LPT blades showed that some blades had sustained levels of thermally-induced microstructural degradation, which may have affected the creep resistance of the alloy and resulted in the blades being susceptible to failure by creep rupture.
Creep rupture was identified as the likely failure mechanism in previous stage-1 LPT blade failures in this engine type investigated by the Australian Transport Safety Bureau and the engine manufacturer. As a result of this occurrence and at the time of writing this report, the engine manufacturer is revising service bulletin SB 72-1113 to expand the range of blade manufacturing batch numbers that had previously been identified as being predisposed to creep-related failure. Blades in the identified batches are to be withdrawn from service as soon as they are next removed from the engine.
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From reading the above, it sounds like a non-event although photos of the engine damage would make any pilot sit up and take notice. The crew read all the right checklists and because the engine settled down after it was throttled back, an in-flight shut down was averted. However, despite this decision in-flight to keep the defective engine running, once the aircraft landed the crew then shut down the engine while taxiing in "as a precaution".
It is many years since this scribe flew jet transports so his comments may be seen by others as outdated and from another era. But there are lessons from the past valid even now. Readers may recall the case of the 737-400 that a long time ago crashed short of East Midlands airport in England killing many passengers. Indeed that particular accident has been used in many CRM and TEM publications as an example of a fatal stuff up by the crew.
Severe vibration caused the crew to shut down an engine during cruise. Mis-identification of the faulty engine was made by both the captain and first officer and the `good` engine was inadvertently shut down. During the descent from cruise altitude with both thrust levers at idle (closed) the severe vibration on the faulty engine practically disappeared. The crew firmly believed the correct engine had been shut down.
During subsequent radar vectors to the ILS (aircraft now on one engine), and after gear and flap selection had been made, power was increased on what the crew blissfully thought was the good engine. To their surprise it failed completely on power application and the 737 crashed into a motorway embankment a few hundred metres from the runway. In other words it was only when power was applied to the defective engine did it give up the ghost.
Turning now to the ATSB report on the QF 737 incident it seems the crew decided not to close down the defective engine and instead leave the close-down until after landing. This ties in with the QRH which states in general that the object is to attempt to recover normal engine operation or shut down the engine if recovery is not possible. Further, the book says run the engine normally or at a reduced thrust setting which is surge and stall free.
In other words, if the engine is running normally at idle there is no need to shut it down. Which is what happened with QF - except the crew were sufficiently concerned about the engine to shut it down
after landing during the taxi in.
One could speculate what would happen if for some reason the aircraft was required to go-around from final approach. Would the crew apply go-around thrust to both engines and risk re-occurrence of the same problem that caused them to use the QRH in the first place? Or would they make a single engine approach with the defective engine at idle and if a go-around was needed it would be on one engine while leaving the defective engine at idle?
From reading similar incident reports over the years, one is struck by the reluctance of crews to make an in-flight shut down - even though post flight investigations revealed significant damage to the engine concerned. Could it be that crews are reluctant to shut down an engine because of perceived media publicity that invariably follows? (lots of aviation mad people with VHF scanners only too eager to ring up the local media). The ensuing media publicity then alarms the
PR people forced to defend the airline image? The danger is the crew could be hung out to dry for upsetting the corporate image.
It used to be that a precautionary in-flight shut down was considered good airmanship because one could never be certain of the extent of engine damage. On the other hand in today's skies, precautionary in-flight engine shut downs can put the crew in the invidious situation of first weighing up good airmanship versus undesirable consequences from management charged with the responsibility of fending off a rapacious media eager for a headline scoop.