In-flight upset - 154 km west of Learmonth, WA, 7 October 2008,

Previous occurrencesThe seat belt manufacturer, aircraft manufacturer, aircraft operator, andinvestigation and regulatory agencies associated with the investigation 229 , had notpreviously been aware of this inadvertent release scenario associated with the seatarmrest.A review of a sample of investigation reports into turbulence accidents identifiedonly two cases where a passenger reported being seated with the seat belt fastenedand that the seat belt became unfastened during the event. In those cases:• Passenger one reported that he checked that his belt was fastened during theflight because it did not seem to tighten well, but no information was providedregarding whether the belt was fastened loose or tight at the time of theturbulence. No problems were found with the belt in a subsequent inspection. 230• Passenger two was carrying a bag on her lap, and examinations found that sucha bag could, if moved sideways, contact the buckle cover and release the seatbelt. 231Relevance to the occurrence flightThe inadvertent release scenario could not occur to a tightly-fastened seat belt, andtherefore the scenario did not occur for at least three of the six passengers whoreported having their belts fastened but were not restrained. However, whether theinadvertent release scenario occurred for any of the other three passengers could notbe determined based on the available information. It is worth noting that there wasno previous knowledge of this scenario actually occurring during an in-flight upset,despite the widespread use of this type of seat belt throughout the aviation industry.It is also worth noting that a seat belt had to be very loosely fastened before thescenario could occur. Seat belts that were loosely fastened would pose a significantinjury risk even if they remained fastened. They would be difficult to keeppositioned across the passenger’s pelvis, and they would also allow significantmovement of the passenger before restraint.Although the six passengers reported that they had their seat belts fastened at thetime of the first in-flight upset, the investigation could not confirm that this was thecase. It is possible that their seat belts may have been inadvertently released prior tothe upset during their movement in the seat during the flight. It is also possible thatthe seat belts inadvertently released due to the movement of their arms or otherobjects located close to the buckle at the time.229230231The investigation agencies included the ATSB, the US National Transportation Safety Board, andthe French Bureau d’Enquêtes et d’Analyses pour la sécurité de l’aviation civile. The regulatoryagencies included the Australian Civil Aviation Safety Authority (CASA), the United StatesFederal Aviation Administration (FAA), and the European Aviation Safety Agency (EASA).Irish Air Accident Investigation Unit report 2002/007 (ATR 42-300, EI-CPT, Mt Errigal,2 December 2001).Japan Transport Safety Board report AA2008-01 (Boeing 767-300, JA611J, 27 km south-east ofNarita, 27 October 2007).- 274 -