NEW : Experts from Britain , France and Canada will help investigate . Title: Why do we have to take a pill every day? The cause of the crash was not immediately known . Moscow ( CNN ) -- The crash is Russia 's worst air disaster since a crash in Yaroslavl last year .
NEW : Experts from Britain , France and Canada will help investigate . Title: Why do we have to take a pill every day? The cause of the crash was not immediately known . The crash is Russia 's worst air disaster since a crash in Yaroslavl last year .