On 25 July 2008, at 09:22 local time, a Boeing 747-438 aircraft departed Hong Kong (HKG) on a scheduled flight to Melbourne (MEL), 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 shortly afterward, and it was reported that most passengers and crew commenced using the masks. After donning their own oxygen masks, the flight crew carried out the ‘cabin altitude non-normal’ checklist items and commenced a descent to a lower altitude, where supplemental breathing oxygen would no longer be required. 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. The aircraft was stopped on the runway for an external inspection, before being towed to the terminal for passenger disembarkation. Subsequent inspection revealed an inverted T-shaped rupture in the lower right side of the fuselage, immediately beneath the wing leading edge-to-fuselage transition fairing (which had been lost during the event). Items of wrapped cargo were observed partially protruding from the rupture, which extended for approximately 2 metres along the length of the aircraft and 1.5 metres vertically. After clearing the baggage and cargo from the forward aircraft hold, 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 into the aircraft hold, rupturing the fuselage in the vicinity of the wing-fuselage leading edge fairing. The cylinder had been propelled upward by the force of the discharge, puncturing the cabin floor and entering the cabin adjacent to the second main cabin door. The cylinder had subsequently impacted the door frame, door handle and overhead panelling, before falling to the cabin floor and exiting the aircraft through the ruptured fuselage. In the context of this event, the inability to physically examine the key item of physical evidence (the failed oxygen cylinder), meant that the only verifiable contributing safety factors were those associated with the occurrence event itself: – During flight, a single pressurised oxygen cylinder failed by rupture; forcefully releasing its contents. – The force of the suddenly-released pressurised contents of the oxygen cylinder locally ruptured the aircraft’s fuselage and allowed the aircraft to depressurise in an uncontrolled manner.