Svarin,
I believe it's unlikely very many pax left their seats due to "inadvertant seatbelt release."
However, the QF72 Nov. 2009 2nd Interim
ATSB TRANSPORT SAFETY REPORT does state that "At least 60 of the 303 passengers were seated without their seatbelts fastened..." That's about twenty percent unfastened during a Singapore to Perth cruise. Could we expect similar proportions for an AF447 Rio to Paris cruise? With quite a few unsold seats on AF447, how many PAX may have been stretched out across two or more unassigned seats for sleep, and were at best but loosly belted?
More from the QF72 report:
Six passengers reported to the ATSB that they were seated with their seatbelt fastened at the time of the first upset, but that the seatbelt became unfastened and did not restrain them in their seats. Three of those passengers advised that they had their seatbelts tightly fastened, and three advised that they had their seatbelts loosely fastened. None of the six passengers could provide details of how their seatbelts released.
As advised in the first Interim Factual Report, the investigation identified a scenario whereby seatbelts could inadvertently release. For this to occur, the seatbelt had to be loosely fastened and the buckle had to be positioned in a vertical orientation underneath the right armrest prior to an upward force being applied. The lift-latch could then catch on the armrest and the buckle release.
The ATSB has conducted further examinations of this inadvertent release scenario on one of the operator’s A330 aircraft. Those examinations found that, for this scenario to occur on those aircraft, the seatbelt had to be adjusted so that there was at least 25 cm of slack in the belt (comparing the length of a firmly-fastened seatbelt with one that was loosely fastened to the minimum extent necessary to enable the inadvertent release scenario to occur).
GB