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Interim No.1

Summary

Interim Factual No.1 report released 6 March 2009

On 25 July 2008, at 0922 local time, a Boeing Company 747-438 aircraft (registered VH-OJK) with 365 persons on board, departed Hong Kong International airport on a scheduled passenger transport flight to Melbourne, Australia. Approximately 55 minutes into the flight, while the aircraft was cruising at 29,000 ft (FL290), a loud bang was heard by passengers and crew, followed by the rapid depressurisation of the cabin. Oxygen masks dropped from the overhead compartments and it was reported that most passengers and crew commenced using the masks. The flight crew carried out the 'cabin altitude non-normal' checklist items and commenced a descent to a lower altitude. A MAYDAY distress radio call was made on the regional air traffic control frequency. After levelling the aircraft at 10,000 ft, the flight crew diverted to Ninoy Aquino International Airport, Manila, where an uneventful visual approach and landing was made.

Inspection of the aircraft by the operator's personnel and Australian Transport Safety Bureau (ATSB) investigators, revealed a rupture in the lower right side of the fuselage, immediately beneath the wing leading edge-to-fuselage transition fairing. The rupture extended for approximately 2 metres along the length of the aircraft and 1.5 metres vertically. It was evident that one passenger oxygen cylinder (number-4 from a bank of seven cylinders along the right side of the cargo hold) had sustained a sudden failure and forceful discharge of its pressurised contents, rupturing the fuselage and propelling the cylinder upward, puncturing the cabin floor and entering the cabin adjacent to the second main cabin door. The cylinder had impacted the door frame, door handle and overhead panelling, before presumably falling to the cabin floor and exiting the aircraft through the ruptured fuselage, as the cylinder was not located within the aircraft.

In the absence of the failed cylinder, the ATSB, with the assistance of the aircraft manufacturer, has obtained a number of exemplar cylinders from the same production batch. A program of engineering assessments is examining the compliance of the cylinders with the original production specification, the damage tolerance of the design, and the potential mechanism for cylinder failure. To date, the investigation has not identified any verifiable deficiency in the cylinder design. Preliminary analyses
of the cabin safety systems and crew/passenger experiences have indicated that the aircraft oxygen systems had operated satisfactorily, despite the damage sustained during the rupture and depressurisation events.

 
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