Aircrew Buzz: Preliminary factual report issued for Qantas Boeing 747 depressurization incident

Friday, August 29, 2008

Preliminary factual report issued for Qantas Boeing 747 depressurization incident

The Australian Transport Safety Bureau (ATSB) has issued a preliminary factual report regarding the in-flight decompression of a Qantas Boeing 747-400 last month. Readers will recall that on July 25, 2008, Qantas Flight QF30 experienced a rapid decompression while en route from Hong Kong to Melbourne. The aircraft (registration number VH-OJK) diverted to Manila, where it made a safe emergency landing. Once on the ground, a large hole in the fuselage was discovered. No one among the passengers and crew on board the flight were injured.

The preliminary factual report issued today by the ATSB reviews the course of events on Flight QF30 and confirms that "the fuselage rupture was aligned with the nominal position of the number-4 passenger emergency oxygen cylinder" in the aircraft's forward cargo hold, and that the oxygen cylinder - one of seven in the bank of cylinders that provided emergency oxygen to the passenger cabin - was missing.

Today's report made clear that one oxygen cylinder had ruptured, and was believed to have caused the breach in the aircraft's pressure hull. How or why the cylinder ruptured has not yet been determined.

The ATSB media release accompanying the report says:

On the basis of the physical damage to the aircraft's forward cargo hold and cabin, it was evident that the number-4 passenger oxygen cylinder sustained a failure that allowed a sudden and complete release of the pressurised contents. The rupture and damage to the aircraft's fuselage was consistent with being produced by the energy associated with that release of pressure. Furthermore, it was evident that as a result of the cylinder failure, the vessel was propelled upward, through the cabin floor and into the cabin space. Damage and impact witness marks found on the structure and fittings around the R2 cabin door showed the trajectory of the cylinder after the failure.

The report includes a number of graphics that illustrate the likely trajectory of the cylinder, based on the observed damage (links below).

The ATSB media release goes on to say:

The investigation to date has also identified other damage to the aircraft, including severing and damage to numerous electrical cables and cable bundles, routed through the lower aircraft fuselage near the point of rupture. In addition, both right side (first officer's) aileron control cables, routed along the right side of the fuselage above the passenger oxygen cylinders, were fractured during the rupture event. However, the aircraft control systems have a redundancy arrangement whereby the first officer's aileron control cables are duplicated by the captain's system, the cables from which were routed along the opposite (left) side of the forward cargo hold. Interlinks between the aileron systems provided the necessary redundancy in this instance, ensuring the continued safety of flight after the event.

Another aspect of the investigation entails cabin safety issues, especially the status of the passenger oxygen masks and equipment. The investigation found that 476 passenger oxygen masks had deployed, and 426 of those had been activated. (Days after the incident, the ATSB had reported that "In all, 484 masks had deployed. Of those, 418 had been activated by pulling on the mask to activate the flow of oxygen.") Of note, the report says that forward crew rest and customer support manager station masks had not deployed.

The investigation is ongoing. Still underway are an engineering investigation into the apparent oxygen cylinder failure; examination of cockpit voice recorder, flight data recorder and quick access recorder information; and a survey of all passengers on the flight.

Links to information released today by the ATSB: