Mechanical failure is speculated as the likely cause of the Christmas plane crash that killed 92. Vladimir Velengurin/AP/Russian Emergency Ministry Press Service hide caption

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Vladimir Velengurin/AP/Russian Emergency Ministry Press Service

A woman mourns at a makeshift memorial for the victims of a jetliner crash outside Pulkovo International Airport in St. Petersburg on Tuesday. Vasily Maximov /AFP/Getty Images hide caption

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Vasily Maximov /AFP/Getty Images

A family leaves flowers and toys at an entrance of Pulkovo airport outside St. Petersburg, Russia, during a day of national mourning for the plane crash victims. Dmitry Lovetsky/AP hide caption

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Dmitry Lovetsky/AP