Preliminary report released 25 October 2010
On 30 August 2010 at approximately 2330 Pacific Daylight Time, a
Boeing 747-438 aircraft, registered VH-OJP, departed San Francisco
International Airport on a scheduled passenger service to Sydney,
Australia. As the aircraft passed through 25,000 ft, the aircraft's
number-4 engine sustained an internal mechanical failure, resulting
in the energetic release of debris and puncturing of the engine
casing and nacelle. The engine was shut down and the flight crew
returned the aircraft to San Francisco, where it landed without
further incident.
Updated: 29 August 2011
Disassembly and examination of the number-4, Rolls-Royce
RB211-524 engine at Hong Kong Aero Engine Services Limited (HAESL)
has been completed under supervision of ATSB investigators, as well
as representatives from the engine manufacturer, airframe
manufacturer, and aircraft operator. Based on the outcomes of the
disassembly, numerous engine components were retained for further,
detailed testing and analysis by the engine manufacturer.
The manufacturer's investigation has concluded that the fracture
and release of a low-pressure turbine (LPT) blade was likely to
have initiated the engine failure. This produced rotor
imbalance forces that resulted in significant damage to the LPT
support bearing. The bearing damage promoted additional
secondary damage to core turbine hardware, to the extent that a
turbine casing was ruptured and low energy blade and nozzle guide
vane debris was released.
An alternative bearing standard, which featured a more robust
construction, had previously been introduced as an optional
replacement part for reasons of continuity of supply for
production. This bearing standard was not fitted in the event
engine. To minimise the risk of complications arising from
rotor imbalance, the engine manufacturer is working with operators
to embody this more robust bearing standard into engines, which, at
the time of writing, is installed in more than 50% of the worldwide
fleet. The engine manufacturer has issued an Alert
Non-Modification Service Bulletin (NMSB72-AG729) to instruct the
installation of this improved bearing across the remainder of the
fleet.
Updated: 7 September 2010
The ATSB investigation team has completed its preliminary
examination of the engine in San Francisco. The engine is now being
shipped to an engine facility in Hong Kong for a detailed
disassembly and examination, under the supervision of ATSB
investigators. The investigation is ongoing and also includes:
- detailed analysis of recorded flight data, with particular
focus on analysis of engine operational parameters
- examination of aircraft maintenance documentation
- interviews with crew and passengers.
This page will provide future updates on any significant
developments as they come to hand.
